publications | Kyle Oman

Available with citation data at ADS and Google Scholar. Also available at ORCiD. Publications with DU affiliation also at DRO. All full-text versions below provided free for personal use.

2024

Hydrodynamical simulations of merging galaxy clusters: giant dark matter particle colliders, powered by gravity

Ellen L. Sirks, David Harvey, Richard Massey, and 7 more authors

(2024) MNRAS 530 3160

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Terrestrial particle accelerators collide charged particles, then watch the trajectory of outgoing debris - but they cannot manipulate dark matter. Fortunately, dark matter is the main component of galaxy clusters, which are continuously pulled together by gravity. We show that galaxy cluster mergers can be exploited as enormous, natural dark matter colliders. We analyse hydrodynamical simulations of a universe containing self- interacting dark matter (SIDM) in which all particles interact via gravity, and dark matter particles can also scatter off each other via a massive mediator. During cluster collisions, SIDM spreads out and lags behind cluster member galaxies. Individual systems can have quirky dynamics that makes them difficult to interpret. Statistically, however, we find that the mean or median of dark matter’s spatial offset in many collisions can be robustly modelled, and is independent of our viewing angle and halo mass even in collisions between unequal-mass systems. If the SIDM cross-section were σ/m = 0.1 cm² g^-1 = 0.18 barn GeV^-1, the ’bulleticity’ lag would be ∼5 per cent that of gas due to ram pressure, and could be detected at 95 per cent confidence level in weak lensing observations of ∼100 well-chosen clusters.
@article{2024MNRAS.530.3160S, author = {{Sirks}, Ellen L. and {Harvey}, David and {Massey}, Richard and {Oman}, Kyle A. and {Robertson}, Andrew and {Frenk}, Carlos and {Everett}, Spencer and {Gill}, Ajay S. and {Lagattuta}, David and {McCleary}, Jacqueline}, title = {{Hydrodynamical simulations of merging galaxy clusters: giant dark matter particle colliders, powered by gravity}}, journal = {\mnras}, keywords = {galaxies: clusters: general, dark matter, cosmology: theory, Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology, High Energy Physics - Theory}, year = {2024}, month = may, volume = {530}, number = {3}, pages = {3160-3170}, doi = {10.1093/mnras/stae1012}, archiveprefix = {arXiv}, eprint = {2405.00140}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024MNRAS.530.3160S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Gas and Star Formation in Satellites of Milky Way Analogs

Michael G. Jones, David J. Sand, Ananthan Karunakaran, and 9 more authors

(2024) ApJ 966 93

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We have imaged the entirety of eight (plus one partial) Milky Way (MW)-like satellite systems, a total of 42 (45) satellites, from the Satellites Around Galactic Analogs II catalog in both Hα and HI with the Canada-France-Hawaii Telescope and the Jansky Very Large Array. In these eight systems we have identified four cases where a satellite appears to be currently undergoing ram pressure stripping (RPS) as its HI gas collides with the circumgalactic medium (CGM) of its host. We also see a clear suppression of gas fraction (M_HI/M_★) with decreasing (projected) satellite-host separation - to our knowledge, the first time this has been observed in a sample of MW-like systems. Comparisons to the Auriga, A Project Of Simulating The Local Environment, and TNG50 cosmological zoom-in simulations show consistent global behavior, but they systematically underpredict gas fractions across all satellites by roughly 0.5 dex. Using a simplistic RPS model, we estimate the average peak CGM density that satellites in these systems have encountered to be logρ_cgm/g cm^-3 ∼-27.3. Furthermore, we see tentative evidence that these satellites are following a specific star formation rate to gas fraction relation that is distinct from field galaxies. Finally, we detect one new gas-rich satellite in the UGC 903 system with an optical size and surface brightness meeting the standard criteria to be considered an ultra-diffuse galaxy.
@article{2024ApJ...966...93J, author = {{Jones}, Michael G. and {Sand}, David J. and {Karunakaran}, Ananthan and {Spekkens}, Kristine and {Oman}, Kyle A. and {Bennet}, Paul and {Besla}, Gurtina and {Crnojevi{\'c}}, Denija and {Cuillandre}, Jean-Charles and {Fielder}, Catherine E. and {Gwyn}, Stephen and {Mutlu-Pakdil}, Bur{\c{c}}in}, title = {{Gas and Star Formation in Satellites of Milky Way Analogs}}, journal = {\apj}, keywords = {Dwarf galaxies, Galaxy quenching, Ram pressure stripped tails, Interstellar atomic gas, Circumgalactic medium, 416, 2040, 2126, 833, 1879, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = may, volume = {966}, number = {1}, eid = {93}, pages = {93}, doi = {10.3847/1538-4357/ad3076}, archiveprefix = {arXiv}, eprint = {2311.02152}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...966...93J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2023

KURVS: the outer rotation curve shapes and dark matter fractions of z ∼1.5 star-forming galaxies

Annagrazia Puglisi, Ugnė Dudzevičiūtė, Mark Swinbank, and 14 more authors

(2023) MNRAS 524 2814

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We present first results from the KMOS Ultra-deep Rotation Velocity Survey (KURVS), aimed at studying the outer rotation curves shape and dark matter content of 22 star-forming galaxies at z ∼1.5. These galaxies represent ’typical’ star-forming discs at z ∼1.5, being located within the star-forming main sequence and stellar mass-size relation with stellar masses 9.5 ≤ log(M_★/M_⊙) ≤ 11.5. We use the spatially resolved Hα emission to extract individual rotation curves out to 4 times the effective radius, on average, or ∼10-15 kpc. Most rotation curves are flat or rising between three and six disc scale radii. Only three objects with dispersion-dominated dynamics (v_rot/σ₀ ∼0.2) have declining outer rotation curves at more than 5σ significance. After accounting for seeing and pressure support, the nine rotation-dominated discs with v_rot/σ₀ ≥ 1.5 have average dark matter fractions of 50±20 per cent at the effective radius, similar to local discs. Together with previous observations of star-forming galaxies at cosmic noon, our measurements suggest a trend of declining dark matter fraction with increasing stellar mass and stellar mass surface density at the effective radius. Measurements of simulated EAGLE galaxies are in quantitative agreement with observations up to log(M_★ R_eff^-2 /M_⊙ kpc^-2) ∼9.2, and overpredict the dark matter fraction of galaxies with higher mass surface densities by a factor of ∼3. We conclude that the dynamics of typical rotationally-supported discs at z ∼1.5 is dominated by dark matter from effective radius scales, in broad agreement with cosmological models. The tension with observations at high stellar mass surface density suggests that the prescriptions for baryonic processes occurring in the most massive galaxies (such as bulge growth and quenching) need to be reassessed.
@article{2023MNRAS.524.2814P, author = {{Puglisi}, Annagrazia and {Dudzevi{\v{c}}i{\={u}}t{\.{e}}}, Ugn{\.{e}} and {Swinbank}, Mark and {Gillman}, Steven and {Tiley}, Alfred L. and {Bower}, Richard G. and {Cirasuolo}, Michele and {Cortese}, Luca and {Glazebrook}, Karl and {Harrison}, Chris and {Ibar}, Edo and {Molina}, Juan and {Obreschkow}, Danail and {Oman}, Kyle A. and {Schaller}, Matthieu and {Shankar}, Francesco and {Sharples}, Ray M.}, title = {{KURVS: the outer rotation curve shapes and dark matter fractions of z $\sim$ 1.5 star-forming galaxies}}, journal = {\mnras}, keywords = {galaxies: evolution, galaxies: high-redshift, galaxies: kinematics and dynamics, Astrophysics - Astrophysics of Galaxies}, year = {2023}, month = sep, volume = {524}, number = {2}, pages = {2814-2835}, doi = {10.1093/mnras/stad1966}, archiveprefix = {arXiv}, eprint = {2305.04382}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2023MNRAS.524.2814P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The north-south asymmetry of the ALFALFA HI velocity width function

Richard A. N. Brooks, Kyle A. Oman, and Carlos S. Frenk

(2023) MNRAS 522 4043

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The number density of extragalactic 21-cm radio sources as a function of their spectral line widths - the HI width function (HIWF) - is a sensitive tracer of the dark matter halo mass function (HMF). The Lambda cold dark matter model predicts that the HMF should be identical everywhere provided it is sampled in sufficiently large volumes, implying that the same should be true of the HI WF. The Arecibo Legacy Fast ALFA (ALFALFA) 21-cm survey measured the HI WF in northern and southern Galactic fields and found a systematically higher number density in the north. At face value, this is in tension with theoretical predictions. We use the Sibelius-DARK N-body simulation and the semi-analytical galaxy formation model GALFORM to create a mock ALFALFA survey. We find that the offset in number density has two origins: the sensitivity of the survey is different in the two fields, which has not been correctly accounted for in previous measurements; and the 1/V_eff algorithm used for completeness corrections does not fully account for biases arising from spatial clustering in the galaxy distribution. The latter is primarily driven by a foreground overdensity in the northern field within 30 Mpc, but more distant structure also plays a role. We provide updated measurements of the ALFALFA HI WF (and HI mass function) correcting for the variations in survey sensitivity. Only when systematic effects such as these are understood and corrected for can cosmological models be tested against the HI WF.
@article{2023MNRAS.522.4043B, author = {{Brooks}, Richard A. N. and {Oman}, Kyle A. and {Frenk}, Carlos S.}, title = {{The north-south asymmetry of the ALFALFA HI velocity width function}}, journal = {\mnras}, keywords = {galaxies: abundances, galaxies: luminosity function, mass function, dark matter, radio lines: galaxies, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2023}, month = jul, volume = {522}, number = {3}, pages = {4043-4058}, doi = {10.1093/mnras/stad1191}, archiveprefix = {arXiv}, eprint = {2211.08092}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2023MNRAS.522.4043B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The many reasons that the rotation curves of low-mass galaxies can fail as tracers of their matter distributions

Eleanor R. Downing, and Kyle A. Oman

(2023) MNRAS 522 3318

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It is routinely assumed that galaxy rotation curves are equal to their circular velocity curves (modulo some corrections) such that they are good dynamical mass tracers. We take a visualization- driven approach to exploring the limits of the validity of this assumption for a sample of 33 low-mass galaxies (60 v_max/km s^-1 120) from the APOSTLE suite of cosmological hydrodynamical simulations. Only three of these have rotation curves nearly equal to their circular velocity curves at z = 0, the rest are undergoing a wide variety of dynamical perturbations. We use our visualizations to guide an assessment of how many galaxies are likely to be strongly perturbed by processes in several categories: mergers/interactions (affecting 6/33 galaxies), bulk radial gas inflows (19/33), vertical gas outflows (15/33), distortions driven by a non-spherical DM halo (17/33), warps (8/33), and winds due to motion through the intergalactic medium (5/33). Most galaxies fall into more than one of these categories; only 5/33 are not in any of them. The sum of these effects leads to an underestimation of the low-velocity slope of the baryonic Tully-Fisher relation (α ∼3.1 instead of α ∼3.9, where M_bar ∝ v^α) that is difficult to avoid, and could plausibly be the source of a significant portion of the observed diversity in low-mass galaxy rotation curve shapes.
@article{2023MNRAS.522.3318D, author = {{Downing}, Eleanor R. and {Oman}, Kyle A.}, title = {{The many reasons that the rotation curves of low-mass galaxies can fail as tracers of their matter distributions}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: kinematics and dynamics, dark matter, Astrophysics - Astrophysics of Galaxies}, year = {2023}, month = jul, volume = {522}, number = {3}, pages = {3318-3336}, doi = {10.1093/mnras/stad868}, archiveprefix = {arXiv}, eprint = {2301.05242}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2023MNRAS.522.3318D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Constraining quenching time-scales in galaxy clusters by forward-modelling stellar ages and quiescent fractions in projected phase space

Andrew M. M. Reeves, Michael J. Hudson, and Kyle A. Oman

(2023) MNRAS 522 1779

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We forward-model mass-weighted stellar ages (MWAs) and quiescent fractions (f_Q) in projected phase space (PPS), using data from the Sloan Digital Sky Survey, to jointly constrain an infall quenching model for galaxies in log (M_vir/M_⊙) > 14 galaxy clusters at z ∼0. We find the average deviation in MWA from the MWA-M_★ relation depends on position in PPS, with a maximum difference between the inner cluster and infalling interloper galaxies of ∼1 Gyr. Our model employs infall information from N-body simulations and stochastic star- formation histories from the UNIVERSEMACHINE model. We find total quenching times of t_Q = 3.7 ± 0.4 Gyr and t_Q = 4.0 ± 0.2 Gyr after first pericentre, for 9 < log (M_★/M_⊙) < 10 and 10 < log (M_★/M_⊙) < 10.5 galaxies, respectively. By using MWAs, we break the degeneracy in time of quenching onset and time-scale of star formation rate (SFR) decline. We find that time of quenching onset relative to pericentre is t_delay=3.5^+0.6_-0.9 Gyr and t_delay=-0.3^+0.8_-1.0 Gyr for 9 < log (M_★/M_⊙) < 10 and 10 < log (M_★/M_⊙) < 10.5 galaxies, respectively, and exponential SFR suppression time-scales are τ_env ≤ 1.0 Gyr for 9 < log (M_★/M_⊙) < 10 galaxies and τ_env ∼2.3 Gyr for 10 < log (M_★/M_⊙) < 10.5 galaxies. Stochastic star formation histories remove the need for rapid infall quenching to maintain the bimodality in the SFR of cluster galaxies; the depth of the green valley prefers quenching onsets close to first pericentre and a longer quenching envelope, in slight tension with the MWA-driven results. Taken together these results suggest that quenching begins close to, or just after pericentre, but the time-scale for quenching to be fully complete is much longer and therefore ram-pressure stripping is not complete on first pericentric passage.
@article{2023MNRAS.522.1779R, author = {{Reeves}, Andrew M. M. and {Hudson}, Michael J. and {Oman}, Kyle A.}, title = {{Constraining quenching time-scales in galaxy clusters by forward-modelling stellar ages and quiescent fractions in projected phase space}}, journal = {\mnras}, keywords = {galaxies: clusters: general, galaxies: evolution, galaxies: haloes, galaxies: star formation, Astrophysics - Astrophysics of Galaxies}, year = {2023}, month = jun, volume = {522}, number = {2}, pages = {1779-1799}, doi = {10.1093/mnras/stad1069}, archiveprefix = {arXiv}, eprint = {2211.09145}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2023MNRAS.522.1779R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The diversity of rotation curves of simulated galaxies with cusps and cores

Finn A. Roper, Kyle A. Oman, Carlos S. Frenk, and 3 more authors

(2023) MNRAS 521 1316

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We use ΛCDM cosmological hydrodynamical simulations to explore the kinematics of gaseous discs in late-type dwarf galaxies. We create high-resolution 21-cm ’observations’ of simulated dwarfs produced in two variations of the EAGLE galaxy formation model: one where supernova-driven gas flows redistribute dark matter and form constant-density central ’cores’, and another where the central ’cusps’ survive intact. We ’observe’ each galaxy along multiple sightlines and derive a rotation curve for each observation using a conventional tilted- ring approach to model the gas kinematics. We find that the modelling process introduces systematic discrepancies between the recovered rotation curve and the actual circular velocity curve driven primarily by (i) non-circular gas orbits within the discs; (ii) the finite thickness of gaseous discs, which leads to overlap of different radii in projection; and (iii) departures from dynamical equilibrium. Dwarfs with dark matter cusps often appear to have a core, whilst the inverse error is less common. These effects naturally reproduce an observed trend which other models struggle to explain: late-type dwarfs with more steeply rising rotation curves appear to be dark matter- dominated in the inner regions, whereas the opposite seems to hold in galaxies with core-like rotation curves. We conclude that if similar effects affect the rotation curves of observed dwarfs, a late-type dwarf population in which all galaxies have sizeable dark matter cores is most likely incompatible with current measurements.
@article{2023MNRAS.521.1316R, author = {{Roper}, Finn A. and {Oman}, Kyle A. and {Frenk}, Carlos S. and {Ben{\'\i}tez-Llambay}, Alejandro and {Navarro}, Julio F. and {Santos-Santos}, Isabel M. E.}, title = {{The diversity of rotation curves of simulated galaxies with cusps and cores}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: kinematics and dynamics, dark matter, Astrophysics - Astrophysics of Galaxies}, year = {2023}, month = may, volume = {521}, number = {1}, pages = {1316-1336}, doi = {10.1093/mnras/stad549}, archiveprefix = {arXiv}, eprint = {2203.16652}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2023MNRAS.521.1316R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2022

The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package

Astropy Collaboration, Adrian M. Price-Whelan, Pey Lian Lim, and 134 more authors

(2022) ApJ 935 167

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The Astropy Project supports and fosters the development of open-source and openly developed Python packages that provide commonly needed functionality to the astronomical community. A key element of the Astropy Project is the core package astropy, which serves as the foundation for more specialized projects and packages. In this article, we summarize key features in the core package as of the recent major release, version 5.0, and provide major updates on the Project. We then discuss supporting a broader ecosystem of interoperable packages, including connections with several astronomical observatories and missions. We also revisit the future outlook of the Astropy Project and the current status of Learn Astropy. We conclude by raising and discussing the current and future challenges facing the Project.

@article{2022ApJ...935..167A,
  author = {{Astropy Collaboration} and {Price-Whelan}, Adrian M. and {Lim}, Pey Lian and {Earl}, Nicholas and {Starkman}, Nathaniel and {Bradley}, Larry and {Shupe}, David L. and {Patil}, Aarya A. and {Corrales}, Lia and {Brasseur}, C. E. and {N{\"o}the}, Maximilian and {Donath}, Axel and {Tollerud}, Erik and {Morris}, Brett M. and {Ginsburg}, Adam and {Vaher}, Eero and {Weaver}, Benjamin A. and {Tocknell}, James and {Jamieson}, William and {van Kerkwijk}, Marten H. and {Robitaille}, Thomas P. and {Merry}, Bruce and {Bachetti}, Matteo and {G{\"u}nther}, H. Moritz and {Aldcroft}, Thomas L. and {Alvarado-Montes}, Jaime A. and {Archibald}, Anne M. and {B{\'o}di}, Attila and {Bapat}, Shreyas and {Barentsen}, Geert and {Baz{\'a}n}, Juanjo and {Biswas}, Manish and {Boquien}, M{\'e}d{\'e}ric and {Burke}, D. J. and {Cara}, Daria and {Cara}, Mihai and {Conroy}, Kyle E. and {Conseil}, Simon and {Craig}, Matthew W. and {Cross}, Robert M. and {Cruz}, Kelle L. and {D'Eugenio}, Francesco and {Dencheva}, Nadia and {Devillepoix}, Hadrien A. R. and {Dietrich}, J{\"o}rg P. and {Eigenbrot}, Arthur Davis and {Erben}, Thomas and {Ferreira}, Leonardo and {Foreman-Mackey}, Daniel and {Fox}, Ryan and {Freij}, Nabil and {Garg}, Suyog and {Geda}, Robel and {Glattly}, Lauren and {Gondhalekar}, Yash and {Gordon}, Karl D. and {Grant}, David and {Greenfield}, Perry and {Groener}, Austen M. and {Guest}, Steve and {Gurovich}, Sebastian and {Handberg}, Rasmus and {Hart}, Akeem and {Hatfield-Dodds}, Zac and {Homeier}, Derek and {Hosseinzadeh}, Griffin and {Jenness}, Tim and {Jones}, Craig K. and {Joseph}, Prajwel and {Kalmbach}, J. Bryce and {Karamehmetoglu}, Emir and {Ka{\l}uszy{\'n}ski}, Miko{\l}aj and {Kelley}, Michael S. P. and {Kern}, Nicholas and {Kerzendorf}, Wolfgang E. and {Koch}, Eric W. and {Kulumani}, Shankar and {Lee}, Antony and {Ly}, Chun and {Ma}, Zhiyuan and {MacBride}, Conor and {Maljaars}, Jakob M. and {Muna}, Demitri and {Murphy}, N. A. and {Norman}, Henrik and {O'Steen}, Richard and {Oman}, Kyle A. and {Pacifici}, Camilla and {Pascual}, Sergio and {Pascual-Granado}, J. and {Patil}, Rohit R. and {Perren}, Gabriel I. and {Pickering}, Timothy E. and {Rastogi}, Tanuj and {Roulston}, Benjamin R. and {Ryan}, Daniel F. and {Rykoff}, Eli S. and {Sabater}, Jose and {Sakurikar}, Parikshit and {Salgado}, Jes{\'u}s and {Sanghi}, Aniket and {Saunders}, Nicholas and {Savchenko}, Volodymyr and {Schwardt}, Ludwig and {Seifert-Eckert}, Michael and {Shih}, Albert Y. and {Jain}, Anany Shrey and {Shukla}, Gyanendra and {Sick}, Jonathan and {Simpson}, Chris and {Singanamalla}, Sudheesh and {Singer}, Leo P. and {Singhal}, Jaladh and {Sinha}, Manodeep and {Sip{\H{o}}cz}, Brigitta M. and {Spitler}, Lee R. and {Stansby}, David and {Streicher}, Ole and {{\v{S}}umak}, Jani and {Swinbank}, John D. and {Taranu}, Dan S. and {Tewary}, Nikita and {Tremblay}, Grant R. and {de Val-Borro}, Miguel and {Van Kooten}, Samuel J. and {Vasovi{\'c}}, Zlatan and {Verma}, Shresth and {de Miranda Cardoso}, Jos{\'e} Vin{\'\i}cius and {Williams}, Peter K. G. and {Wilson}, Tom J. and {Winkel}, Benjamin and {Wood-Vasey}, W. M. and {Xue}, Rui and {Yoachim}, Peter and {Zhang}, Chen and {Zonca}, Andrea and {Astropy Project Contributors}},
  title = {{The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package}},
  journal = {\apj},
  keywords = {Astronomy software, Open source software, Astronomy data analysis, 1855, 1866, 1858, Astrophysics - Instrumentation and Methods for Astrophysics},
  year = {2022},
  month = aug,
  volume = {935},
  number = {2},
  eid = {167},
  pages = {167},
  doi = {10.3847/1538-4357/ac7c74},
  archiveprefix = {arXiv},
  eprint = {2206.14220},
  primaryclass = {astro-ph.IM},
  adsurl = {https://ui.adsabs.harvard.edu/abs/2022ApJ...935..167A},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System},
}

Using EAGLE simulations to study the effect of observational constraints on the determination of HI asymmetries in galaxies

Pooja V. Bilimogga, Kyle A. Oman, Marc A. W. Verheijen, and 1 more author

(2022) MNRAS 513 5310

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We investigate the effect of observational constraints such as signal- to-noise (S/N) ratio, resolution, and column density level on the HI morphological asymmetry (A_mod) and the effect of noise on the HI global profile (A_flux) asymmetry indices. Using mock galaxies from the EAGLE simulations, we find an optimal combination of the observational constraints that are required for a robust measurement of the A_mod value of a galaxy: a column density threshold of 5 × 10¹⁹ cm^-2 or lower at a minimal S/N of 3 and a galaxy resolved with atleast 11 beams. We also use mock galaxies to investigate the effect of noise on the A_flux values and conclude that a global profile with S/N greater than 6 is required to achieve a robust measurement of asymmetry. We investigate the relation between A_mod and A_flux indices and find them to be uncorrelated, which implies that A_flux values cannot be used to predict morphological asymmetries in galaxies.
@article{2022MNRAS.513.5310B, author = {{Bilimogga}, Pooja V. and {Oman}, Kyle A. and {Verheijen}, Marc A. W. and {van der Hulst}, Thijs}, title = {{Using EAGLE simulations to study the effect of observational constraints on the determination of HI asymmetries in galaxies}}, journal = {\mnras}, keywords = {methods: data analysis, methods: miscellaneous, galaxies: structure, Astrophysics - Astrophysics of Galaxies}, year = {2022}, month = jul, volume = {513}, number = {4}, pages = {5310-5327}, doi = {10.1093/mnras/stac1213}, archiveprefix = {arXiv}, eprint = {2205.00675}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2022MNRAS.513.5310B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
No need for dark matter: resolved kinematics of the ultra-diffuse galaxy AGC 114905

Pavel E. Mancera Piña, Filippo Fraternali, Tom Oosterloo, and 3 more authors

(2022) MNRAS 512 3230

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We present new HI interferometric observations of the gas-rich ultra- diffuse galaxy AGC 114905, which previous work, based on low- resolution data, identified as an outlier of the baryonic Tully- Fisher relation. The new observations, at a spatial resolution ∼2.5 times higher than before, reveal a regular HI disc rotating at about 23 km s^-1. Our kinematic parameters, recovered with a robust 3D kinematic modelling fitting technique, show that the flat part of the rotation curve is reached. Intriguingly, the rotation curve can be explained almost entirely by the baryonic mass distribution alone. We show that a standard cold dark matter halo that follows the concentration-halo mass relation fails to reproduce the amplitude of the rotation curve by a large margin. Only a halo with an extremely (and arguably unfeasible) low concentration reaches agreement with the data. We also find that the rotation curve of AGC 114905 deviates strongly from the predictions of modified Newtonian dynamics. The inclination of the galaxy, which is measured independently from our modelling, remains the largest uncertainty in our analysis, but the associated errors are not large enough to reconcile the galaxy with the expectations of cold dark matter or modified Newtonian dynamics.
@article{2022MNRAS.512.3230M, author = {{Mancera Pi{\~n}a}, Pavel E. and {Fraternali}, Filippo and {Oosterloo}, Tom and {Adams}, Elizabeth A. K. and {Oman}, Kyle A. and {Leisman}, Lukas}, title = {{No need for dark matter: resolved kinematics of the ultra-diffuse galaxy AGC 114905}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: formation, galaxies: irregular, galaxies: kinematics and dynamics, dark matter, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2022}, month = may, volume = {512}, number = {3}, pages = {3230-3242}, doi = {10.1093/mnras/stab3491}, archiveprefix = {arXiv}, eprint = {2112.00017}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2022MNRAS.512.3230M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The effects of self-interacting dark matter on the stripping of galaxies that fall into clusters

Ellen L. Sirks, Kyle A. Oman, Andrew Robertson, and 2 more authors

(2022) MNRAS 511 5927

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We use the Cluster-EAGLE (C-EAGLE) hydrodynamical simulations to investigate the effects of self-interacting dark matter (SIDM) on galaxies as they fall into clusters. We find that SIDM galaxies follow similar orbits to their cold dark matter (CDM) counterparts, but end up with ∼25 per cent less mass by the present day. One in three SIDM galaxies is entirely disrupted, compared to one in five CDM galaxies. However, the excess stripping will be harder to observe than suggested by previous DM-only simulations because the most stripped galaxies form cores and also lose stars: The most discriminating objects become unobservable. The best test will be to measure the stellar-to-halo mass relation (SHMR) for galaxies with stellar mass 10¹⁰-10¹¹ M_⊙. This is 8 times higher in a cluster than in the field for a CDM universe, but 13 times higher for an SIDM universe. Given intrinsic scatter in the SHMR, these models could be distinguished with noise-free galaxy-galaxy strong lensing of ∼32 cluster galaxies.
@article{2022MNRAS.511.5927S, author = {{Sirks}, Ellen L. and {Oman}, Kyle A. and {Robertson}, Andrew and {Massey}, Richard and {Frenk}, Carlos}, title = {{The effects of self-interacting dark matter on the stripping of galaxies that fall into clusters}}, journal = {\mnras}, keywords = {galaxies: clusters: general, galaxies: haloes, dark matter, cosmology: theory, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies}, year = {2022}, month = apr, volume = {511}, number = {4}, pages = {5927-5935}, doi = {10.1093/mnras/stac406}, archiveprefix = {arXiv}, eprint = {2109.03257}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2022MNRAS.511.5927S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The ALFALFA HI velocity width function

Kyle A. Oman

(2022) MNRAS 509 3268

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We make the most precise determination to date of the number density of extragalactic 21-cm radio sources as a function of their spectral line widths - the HI velocity width function (HIWF) - based on 21,827 sources from the final 7000 deg² data release of the Arecibo Legacy Fast ALFA (ALFALFA) survey. The number density of sources as a function of their neutral hydrogen masses - the HI mass function (HIMF) - has previously been reported to have a significantly different low- mass slope and ’knee mass’ in the two sky regions surveyed during ALFALFA. In contrast with this, we find that the shape of the HIWF in the same two sky regions is remarkably similar, consistent with being identical within the confidence intervals implied by the data (but the overall normalization differs). The spatial uniformity of the HIWF implies that it is likely a stable tracer of the mass function of dark matter haloes, in spite of the environmental processes to which the measured variation in the HIMF are attributed, at least for galaxies containing enough neutral hydrogen to be detected. This insensitivity of the HIWF to galaxy formation and evolution can be exploited to turn it into a powerful constraint on cosmological models as future surveys yield increasingly precise measurements. We also report on the possible influence of a previously overlooked systematic error affecting the HIWF, which may plausibly see its low-velocity slope steepen by ∼40 per cent in analyses of future, deeper surveys. Finally, we provide an updated estimate of the ALFALFA completeness limit.
@article{2022MNRAS.509.3268O, author = {{Oman}, Kyle A.}, title = {{The ALFALFA HI velocity width function}}, journal = {\mnras}, keywords = {galaxies: abundances, galaxies: luminosity function, mass function, dark matter, radio lines: galaxies, Astrophysics - Astrophysics of Galaxies}, year = {2022}, month = jan, volume = {509}, number = {3}, pages = {3268-3284}, doi = {10.1093/mnras/stab3164}, archiveprefix = {arXiv}, eprint = {2108.08856}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2022MNRAS.509.3268O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2021

Star formation histories of Coma cluster galaxies matched to simulated orbits hint at quenching around first pericenter

A. K. Upadhyay, K. A. Oman, and S. C. Trager

(2021) A&A 652 A16

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Context. The star formation in galaxies in present-day clusters has almost entirely been shut down, but the exact mechanism that quenched these galaxies is still uncertain. Aims: By tracing the orbital and star formation histories of galaxies within the Coma cluster, we seek to understand the role of the high-density cluster environment in quenching these galaxies. Methods: We combine star formation histories extracted from high-signal-to-noise spectra of 11 early-type galaxies around the center of the Coma cluster with probability distributions for their orbital parameters obtained using an N-body simulation to connect their orbital and star formation histories. Results: We find that all 11 galaxies likely quenched near their first pericentric approach. Higher stellar mass galaxies (log(M_★/M_⊙) > 10) had formed a higher fraction of their stellar mass (more than ∼90%) than their lower mass counterparts (∼80-90%) by the time they fell into the cluster (when they cross 2.5r_vir). We find that the expected infall occurred around z ∼0.6, followed by the first pericentric passage ∼4 Gyr later. Galaxies in our sample formed a significant fraction of their stellar mass, up to 15%, between infall and first pericenter, and had assembled more than ∼98% of their cumulative stellar mass by first pericenter. Conclusions: Unlike previous low-redshift studies that suggest that star formation continues until about first apocenter or later, the high percentage of stellar mass already formed by first pericenter in our sample galaxies points to star formation ceasing within a gigayear after the first pericentric passage. We consider the possible physical mechanisms driving quenching and find that our results resemble the situation in clusters at z ∼1, where active stripping of gas (ram-pressure or tidally driven) seems to be required to quench satellites by their first pericentric passage. However, a larger sample will be required to conclusively account for the unknown fraction of preprocessed satellites in the Coma cluster.
@article{2021A&A...652A..16U, author = {{Upadhyay}, A. K. and {Oman}, K. A. and {Trager}, S. C.}, title = {{Star formation histories of Coma cluster galaxies matched to simulated orbits hint at quenching around first pericenter}}, journal = {\aap}, keywords = {galaxies: clusters: individual: Coma cluster, galaxies: clusters: general, galaxies: evolution, galaxies: star formation, Astrophysics - Astrophysics of Galaxies}, year = {2021}, month = aug, volume = {652}, eid = {A16}, pages = {A16}, doi = {10.1051/0004-6361/202141036}, archiveprefix = {arXiv}, eprint = {2104.04388}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2021A&A...652A..16U}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Satellites around Milky Way Analogs: Tension in the Number and Fraction of Quiescent Satellites Seen in Observations versus Simulations

Ananthan Karunakaran, Kristine Spekkens, Kyle A. Oman, and 13 more authors

(2021) ApJL 916 L19

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We compare the star-forming properties of satellites around Milky Way (MW) analogs from the Stage II release of the Satellites Around Galactic Analogs Survey (SAGA-II) to those from the APOSTLE and Auriga cosmological zoom-in simulation suites. We use archival GALEX UV imaging as a star formation indicator for the SAGA-II sample and derive star formation rates (SFRs) to compare with those from APOSTLE and Auriga. We compare our detection rates from the NUV and FUV bands to the SAGA-II Hα detections and find that they are broadly consistent with over 85% of observed satellites detected in all three tracers. We apply the same spatial selection criteria used around SAGA-II hosts to select satellites around the MW-like hosts in APOSTLE and Auriga. We find very good overall agreement in the derived SFRs for the star-forming satellites as well as the number of star-forming satellites per host in observed and simulated samples. However, the number and fraction of quenched satellites in the SAGA-II sample are significantly lower than those in APOSTLE and Auriga below a stellar mass of M_★ ∼10⁸ M_⊙, even when the SAGA-II incompleteness and interloper corrections are included. This discrepancy is robust with respect to the resolution of the simulations and persists when alternative star formation tracers are employed. We posit that this disagreement is not readily explained by vagaries in the observed or simulated samples considered here, suggesting a genuine discrepancy that may inform the physics of satellite populations around MW analogs.
@article{2021ApJ...916L..19K, author = {{Karunakaran}, Ananthan and {Spekkens}, Kristine and {Oman}, Kyle A. and {Simpson}, Christine M. and {Fattahi}, Azadeh and {Sand}, David J. and {Bennet}, Paul and {Crnojevi{\'c}}, Denija and {Frenk}, Carlos S. and {G{\'o}mez}, Facundo A. and {Grand}, Robert J. J. and {Jones}, Michael G. and {Marinacci}, Federico and {Mutlu-Pakdil}, Bur{\c{c}}in and {Navarro}, Julio F. and {Zaritsky}, Dennis}, title = {{Satellites around Milky Way Analogs: Tension in the Number and Fraction of Quiescent Satellites Seen in Observations versus Simulations}}, journal = {\apjl}, keywords = {Dwarf galaxies, Galaxy evolution, Galaxy quenching, Quenched galaxies, Star formation, 416, 594, 2040, 2016, 1569, Astrophysics - Astrophysics of Galaxies}, year = {2021}, month = aug, volume = {916}, number = {2}, eid = {L19}, pages = {L19}, doi = {10.3847/2041-8213/ac0e3a}, archiveprefix = {arXiv}, eprint = {2105.09321}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2021ApJ...916L..19K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The weak lensing radial acceleration relation: Constraining modified gravity and cold dark matter theories with KiDS-1000

Margot M. Brouwer, Kyle A. Oman, Edwin A. Valentijn, and 22 more authors

(2021) A&A 650 A113

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We present measurements of the radial gravitational acceleration around isolated galaxies, comparing the expected gravitational acceleration given the baryonic matter (g_bar) with the observed gravitational acceleration (g_obs), using weak lensing measurements from the fourth data release of the Kilo- Degree Survey (KiDS-1000). These measurements extend the radial acceleration relation (RAR), traditionally measured using galaxy rotation curves, by 2 decades in g_obs into the low- acceleration regime beyond the outskirts of the observable galaxy. We compare our RAR measurements to the predictions of two modified gravity (MG) theories: modified Newtonian dynamics and Verlinde’s emergent gravity (EG). We find that the measured relation between g_obs and g_bar agrees well with the MG predictions. In addition, we find a difference of at least 6σ between the RARs of early- and late-type galaxies (split by Sérsic index and u-r colour) with the same stellar mass. Current MG theories involve a gravity modification that is independent of other galaxy properties, which would be unable to explain this behaviour, although the EG theory is still limited to spherically symmetric static mass models. The difference might be explained if only the early-type galaxies have significant (M_gas ≈ M_★) circumgalactic gaseous haloes. The observed behaviour is also expected in Λ-cold dark matter (ΛCDM) models where the galaxy-to-halo mass relation depends on the galaxy formation history. We find that MICE, a ΛCDM simulation with hybrid halo occupation distribution modelling and abundance matching, reproduces the observed RAR but significantly differs from BAHAMAS, a hydrodynamical cosmological galaxy formation simulation. Our results are sensitive to the amount of circumgalactic gas; current observational constraints indicate that the resulting corrections are likely moderate. Measurements of the lensing RAR with future cosmological surveys (such as Euclid) will be able to further distinguish between MG and ΛCDM models if systematic uncertainties in the baryonic mass distribution around galaxies are reduced.
@article{2021A&A...650A.113B, author = {{Brouwer}, Margot M. and {Oman}, Kyle A. and {Valentijn}, Edwin A. and {Bilicki}, Maciej and {Heymans}, Catherine and {Hoekstra}, Henk and {Napolitano}, Nicola R. and {Roy}, Nivya and {Tortora}, Crescenzo and {Wright}, Angus H. and {Asgari}, Marika and {van den Busch}, Jan Luca and {Dvornik}, Andrej and {Erben}, Thomas and {Giblin}, Benjamin and {Graham}, Alister W. and {Hildebrandt}, Hendrik and {Hopkins}, Andrew M. and {Kannawadi}, Arun and {Kuijken}, Konrad and {Liske}, Jochen and {Shan}, HuanYuan and {Tr{\"o}ster}, Tilman and {Verlinde}, Erik and {Visser}, Manus}, title = {{The weak lensing radial acceleration relation: Constraining modified gravity and cold dark matter theories with KiDS-1000}}, journal = {\aap}, keywords = {gravitational lensing: weak, methods: statistical, surveys, galaxies: halos, dark matter, cosmology: theory, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology, High Energy Physics - Theory}, year = {2021}, month = jun, volume = {650}, eid = {A113}, pages = {A113}, doi = {10.1051/0004-6361/202040108}, archiveprefix = {arXiv}, eprint = {2106.11677}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2021A&A...650A.113B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Velocity-dependent J-factors for annihilation radiation from cosmological simulations

Erin Board, Nassim Bozorgnia, Louis E. Strigari, and 6 more authors

(2021) JCAP 2021 070

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We determine the dark matter pair-wise relative velocity distribution in a set of Milky Way-like halos in the Auriga and APOSTLE simulations. Focusing on the smooth halo component, the relative velocity distribution is well-described by a Maxwell-Boltzmann distribution over nearly all radii in the halo. We explore the implications for velocity-dependent dark matter annihilation, focusing on four models which scale as different powers of the relative velocity: Sommerfeld, s-wave, p-wave, and d-wave models. We show that the J-factors scale as the moments of the relative velocity distribution, and that the halo-to-halo scatter is largest for d-wave, and smallest for Sommerfeld models. The J-factor is strongly correlated with the dark matter density in the halo, and is very weakly correlated with the velocity dispersion. This implies that if the dark matter density in the Milky Way can be robustly determined, one can accurately predict the dark matter annihilation signal, without the need to identify the dark matter velocity distribution in the Galaxy.
@article{2021JCAP...04..070B, author = {{Board}, Erin and {Bozorgnia}, Nassim and {Strigari}, Louis E. and {Grand}, Robert J. J. and {Fattahi}, Azadeh and {Frenk}, Carlos S. and {Marinacci}, Federico and {Navarro}, Julio F. and {Oman}, Kyle A.}, title = {{Velocity-dependent J-factors for annihilation radiation from cosmological simulations}}, journal = {\jcap}, keywords = {dark matter simulations, dark matter theory, hydrodynamical simulations, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies, High Energy Physics - Phenomenology}, year = {2021}, month = apr, volume = {2021}, number = {4}, eid = {070}, pages = {070}, doi = {10.1088/1475-7516/2021/04/070}, archiveprefix = {arXiv}, eprint = {2101.06284}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2021JCAP...04..070B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
A homogeneous measurement of the delay between the onsets of gas stripping and star formation quenching in satellite galaxies of groups and clusters

Kyle A. Oman, Yannick M. Bahé, Julia Healy, and 3 more authors

(2021) MNRAS 501 5073

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We combine orbital information from N-body simulations with an analytic model for star formation quenching and SDSS observations to infer the differential effect of the group/cluster environment on star formation in satellite galaxies. We also consider a model for gas stripping, using the same input supplemented with HI fluxes from the ALFALFA survey. The models are motivated by and tested on the Hydrangea cosmological hydrodynamical simulation suite. We recover the characteristic times when satellite galaxies are stripped and quenched. Stripping in massive (M_vir ∼10^14.5 M_⊙) clusters typically occurs at or just before the first pericentric passage. Lower mass (∼10^13.5 M_⊙) groups strip their satellites on a significantly longer (by ∼3 Gyr) time-scale. Quenching occurs later: Balmer emission lines typically fade ∼3.5 Gyr (5.5 Gyr) after first pericentre in clusters (groups), followed a few hundred Myr later by reddenning in (g-r) colour. These ’delay time-scales’ are remarkably constant across the entire satellite stellar mass range probed (∼10^9.5-10¹¹ M_⊙), a feature closely tied to our treatment of ’group pre-processing’. The lowest mass groups in our sample (∼10^12.5 M_⊙) strip and quench their satellites extremely inefficiently: typical time-scales may approach the age of the Universe. Our measurements are qualitatively consistent with the ’delayed-then-rapid’ quenching scenario advocated for by several other studies, but we find significantly longer delay times. Our combination of a homogeneous analysis and input catalogues yields new insight into the sequence of events leading to quenching across wide intervals in host and satellite mass.
@article{2021MNRAS.501.5073O, author = {{Oman}, Kyle A. and {Bah{\'e}}, Yannick M. and {Healy}, Julia and {Hess}, Kelley M. and {Hudson}, Michael J. and {Verheijen}, Marc A. W.}, title = {{A homogeneous measurement of the delay between the onsets of gas stripping and star formation quenching in satellite galaxies of groups and clusters}}, journal = {\mnras}, keywords = {galaxies: clusters: general, galaxies: evolution, galaxies: groups: general, Astrophysics - Astrophysics of Galaxies}, year = {2021}, month = mar, volume = {501}, number = {4}, pages = {5073-5095}, doi = {10.1093/mnras/staa3845}, archiveprefix = {arXiv}, eprint = {2009.00667}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2021MNRAS.501.5073O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Stellar splashback: the edge of the intracluster light

Alis J. Deason, Kyle A. Oman, Azadeh Fattahi, and 8 more authors

(2021) MNRAS 500 4181

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We examine the outskirts of galaxy clusters in the C-EAGLE simulations to quantify the ’edges’ of the stellar and dark matter distribution. The radius of the steepest slope in the dark matter, commonly used as a proxy for the splashback radius, is located at ∼r_{200 m}; the strength and location of this feature depends on the recent mass accretion rate, in good agreement with previous work. Interestingly, the stellar distribution (or intracluster light, ICL) also has a well- defined edge, which is directly related to the splashback radius of the halo. Thus, detecting the edge of the ICL can provide an independent measure of the physical boundary of the halo, and the recent mass accretion rate. We show that these caustics can also be seen in the projected density profiles, but care must be taken to account for the influence of substructures and other non-diffuse material, which can bias and/or weaken the signal of the steepest slope. This is particularly important for the stellar material, which has a higher fraction bound in subhaloes than the dark matter. Finally, we show that the ’stellar splashback’ feature is located beyond current observational constraints on the ICL, but these large projected distances (≫1 Mpc) and low surface brightnesses (μ ≫ 32 mag arcsec^-2) can be reached with upcoming observational facilities such as the Vera C. Rubin Observatory, the Nancy Grace Roman Space Telescope, and Euclid.
@article{2021MNRAS.500.4181D, author = {{Deason}, Alis J. and {Oman}, Kyle A. and {Fattahi}, Azadeh and {Schaller}, Matthieu and {Jauzac}, Mathilde and {Zhang}, Yuanyuan and {Montes}, Mireia and {Bah{\'e}}, Yannick M. and {Dalla Vecchia}, Claudio and {Kay}, Scott T. and {Evans}, Tilly A.}, title = {{Stellar splashback: the edge of the intracluster light}}, journal = {\mnras}, keywords = {methods: numerical, galaxies: clusters: general, galaxies: haloes, dark matter, Astrophysics - Astrophysics of Galaxies}, year = {2021}, month = jan, volume = {500}, number = {3}, pages = {4181-4192}, doi = {10.1093/mnras/staa3590}, archiveprefix = {arXiv}, eprint = {2010.02937}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2021MNRAS.500.4181D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2020

To β or not to β: can higher order Jeans analysis break the mass-anisotropy degeneracy in simulated dwarfs?

A. Genina, J. I. Read, C. S. Frenk, and 6 more authors

(2020) MNRAS 498 144

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We test a non-parametric higher order Jeans analysis method, GravSphere, on 32 simulated dwarf galaxies comparable to classical Local Group dwarfs like Fornax. The galaxies are selected from A Project Of Simulating The Local Environment (APOSTLE) suite of cosmological hydrodynamics simulations with cold dark matter (CDM) and self-interacting dark matter (SIDM) models, allowing us to investigate cusps and cores in density distributions. We find that, for CDM dwarfs, the recovered enclosed mass profiles have a bias of no more than 10 per cent, with a 50 per cent scatter in the inner regions and a 20 per cent scatter near the half-light radius, consistent with standard mass estimators. The density profiles are also recovered with a bias of no more than 10 per cent and a scatter of 30 per cent in the inner regions. For SIDM dwarfs, the mass and density profiles are recovered within our 95 per cent confidence intervals but are biased towards cuspy dark matter distributions. This is mainly due to a lack of sufficient constraints from the data. We explore the sources of scatter in the accuracy of the recovered profiles and suggest a χ² statistic to separate successful models from biased ones. Finally, we show that the uncertainties on the mass profiles obtained with GravSphere are smaller than those for comparable Jeans methods and that they can be further improved if stronger priors, motivated by cosmological simulations, are placed on the velocity anisotropy. We conclude that GravSphere is a promising Jeans-based approach for modelling dark matter distributions in dwarf galaxies.
@article{2020MNRAS.498..144G, author = {{Genina}, A. and {Read}, J. I. and {Frenk}, C. S. and {Cole}, S. and {Ben{\'\i}tez-Llambay}, A. and {Ludlow}, A. D. and {Navarro}, J. F. and {Oman}, K. A. and {Robertson}, A.}, title = {{To β or not to β: can higher order Jeans analysis break the mass-anisotropy degeneracy in simulated dwarfs?}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: kinematics and dynamics, dark matter, Astrophysics - Astrophysics of Galaxies}, year = {2020}, month = oct, volume = {498}, number = {1}, pages = {144-163}, doi = {10.1093/mnras/staa2352}, archiveprefix = {arXiv}, eprint = {1911.09124}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2020MNRAS.498..144G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The edge of the Galaxy

Alis J. Deason, Azadeh Fattahi, Carlos S. Frenk, and 5 more authors

(2020) MNRAS 496 3929

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We use cosmological simulations of isolated Milky Way (MW)-mass galaxies, as well as Local Group (LG) analogues, to define the ’edge’ - a caustic manifested in a drop in density or radial velocity - of Galactic-sized haloes, both in dark matter and in stars. In the dark matter, we typically identify two caustics: the outermost caustic located at ∼1.4r_200m, corresponding to the ’splashback’ radius, and a second caustic located at ∼0.6r_200m, which likely corresponds to the edge of the virialized material that has completed at least two pericentric passages. The splashback radius is ill defined in LG-type environments where the haloes of the two galaxies overlap. However, the second caustic is less affected by the presence of a companion, and is a more useful definition for the boundary of the MW halo. Curiously, the stellar distribution also has a clearly defined caustic, which, in most cases, coincides with the second caustic of the dark matter. This can be identified in both radial density and radial velocity profiles, and should be measurable in future observational programmes. Finally, we show that the second caustic can also be identified in the phase-space distribution of dwarf galaxies in the LG. Using the current dwarf galaxy population, we predict the edge of the MW halo to be 292 ± 61 kpc.
@article{2020MNRAS.496.3929D, author = {{Deason}, Alis J. and {Fattahi}, Azadeh and {Frenk}, Carlos S. and {Grand}, Robert J. J. and {Oman}, Kyle A. and {Garrison-Kimmel}, Shea and {Simpson}, Christine M. and {Navarro}, Julio F.}, title = {{The edge of the Galaxy}}, journal = {\mnras}, keywords = {Galaxy: halo, galaxies: haloes, galaxies: kinematics and dynamics, Local Group, methods: numerical, Astrophysics - Astrophysics of Galaxies}, year = {2020}, month = aug, volume = {496}, number = {3}, pages = {3929-3942}, doi = {10.1093/mnras/staa1711}, archiveprefix = {arXiv}, eprint = {2002.09497}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2020MNRAS.496.3929D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Massive disc galaxies too dominated by dark matter in cosmological hydrodynamical simulations

A. Marasco, L. Posti, K. Oman, and 3 more authors

(2020) A&A 640 A70

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We investigated the disc-halo connection in massive (M_★ > 5×10¹⁰ M_⊙) disc galaxies from the cosmological hydrodynamical simulations EAGLE and IllustrisTNG, and compared this connection with that inferred from the study of HI rotation curves in nearby massive spirals from the Spitzer Photometry and Accurate Rotation Curves dataset. We find that discrepancies between the simulated and observed discs arise both on global and local scales. Globally, the simulated discs inhabit halos that are a factor ∼4 (in EAGLE) and ∼2 (in IllustrisTNG) more massive than those derived from the rotation curve analysis of the observed dataset. We also used synthetic rotation curves of the simulated discs to demonstrate that the recovery of the halo masses from rotation curves are not systematically biased. We find that the simulations predict systems dominated by dark matter with stellar-to-total enclosed mass ratios that are a factor of 1.5-2 smaller than real galaxies at all radii. This is an alternative manifestation of the ‘failed feedback problem,’ since it indicates that simulated halos hosting massive discs have been too inefficient at converting their baryons into stars, possibly owing to an overly efficient stellar and/or AGN feedback implementation. Full Table A.1 is only available at the CDS via anonymous ftp to <A href=“http:// cdsarc.u-strasbg.fr/”>http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href=“http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/640/A70”>http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/640/A70</A>
@article{2020A&A...640A..70M, author = {{Marasco}, A. and {Posti}, L. and {Oman}, K. and {Famaey}, B. and {Cresci}, G. and {Fraternali}, F.}, title = {{Massive disc galaxies too dominated by dark matter in cosmological hydrodynamical simulations}}, journal = {\aap}, keywords = {galaxies: kinematics and dynamics, galaxies: halos, galaxies: spiral, methods: numerical, Astrophysics - Astrophysics of Galaxies}, year = {2020}, month = aug, volume = {640}, eid = {A70}, pages = {A70}, doi = {10.1051/0004-6361/202038326}, archiveprefix = {arXiv}, eprint = {2005.01724}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2020A&A...640A..70M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Robust HI kinematics of gas-rich ultra-diffuse galaxies: hints of a weak-feedback formation scenario

Pavel E. Mancera Piña, Filippo Fraternali, Kyle A. Oman, and 15 more authors

(2020) MNRAS 495 3636

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We study the gas kinematics of a sample of six isolated gas-rich low surface brightness galaxies, of the class called ultra-diffuse galaxies (UDGs). These galaxies have recently been shown to be outliers from the baryonic Tully-Fisher relation (BTFR), as they rotate much slower than expected given their baryonic mass, and to have a baryon fraction similar to the cosmological mean. By means of a 3D kinematic modelling fitting technique, we show that the HI in our UDGs is distributed in ’thin’ regularly rotating discs and we determine their rotation velocity and gas velocity dispersion. We revisit the BTFR adding galaxies from other studies. We find a previously unknown trend between the deviation from the BTFR and the exponential disc scale length valid for dwarf galaxies with circular speeds ≲ 45 km s^-1, with our UDGs being at the extreme end. Based on our findings, we suggest that the high baryon fractions of our UDGs may originate due to the fact that they have experienced weak stellar feedback, likely due to their low star formation rate surface densities, and as a result they did not eject significant amounts of gas out of their discs. At the same time, we find indications that our UDGs may have higher-than-average stellar specific angular momentum, which can explain their large optical scale lengths.
@article{2020MNRAS.495.3636M, author = {{Mancera Pi{\~n}a}, Pavel E. and {Fraternali}, Filippo and {Oman}, Kyle A. and {Adams}, Elizabeth A. K. and {Bacchini}, Cecilia and {Marasco}, Antonino and {Oosterloo}, Tom and {Pezzulli}, Gabriele and {Posti}, Lorenzo and {Leisman}, Lukas and {Cannon}, John M. and {di Teodoro}, Enrico M. and {Gault}, Lexi and {Haynes}, Martha P. and {Reiter}, Kameron and {Rhode}, Katherine L. and {Salzer}, John J. and {Smith}, Nicholas J.}, title = {{Robust HI kinematics of gas-rich ultra-diffuse galaxies: hints of a weak-feedback formation scenario}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: evolution, galaxies: formation, galaxies: fundamental parameters, galaxies: general, galaxies: kinematics and dynamics, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2020}, month = jul, volume = {495}, number = {4}, pages = {3636-3655}, doi = {10.1093/mnras/staa1256}, archiveprefix = {arXiv}, eprint = {2004.14392}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2020MNRAS.495.3636M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Observational constraints on the slope of the radial acceleration relation at low accelerations

Kyle A. Oman, Margot M. Brouwer, Aaron D. Ludlow, and 1 more author

(2020) arXiv 2006.06700

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The radial acceleration relation (RAR) locally relates the ‘observed’ acceleration inferred from the dynamics of a system to the acceleration implied by its baryonic matter distribution. The relation as traced by galaxy rotation curves is one-to-one with remarkably little scatter, implying that the dynamics of a system can be predicted simply by measuring its density profile as traced by e.g. stellar light or gas emission lines. Extending the relation to accelerations below those usually probed by practically observable kinematic tracers is challenging, especially once accounting for faintly emitting baryons, such as the putative warm-hot intergalactic medium, becomes important. We show that in the low-acceleration regime, the (inverted) RAR predicts an unphysical, declining enclosed baryonic mass profile for systems with ‘observed’ acceleration profiles steeper than g_obs ∝ r^-1 (corresponding to density profiles steeper than isothermal - ρ(r) ∝ r^-2). If the RAR is tantamount to a natural law, such acceleration profiles cannot exist. We apply this argument to test the compatibility of an extrapolation of the rotation curve-derived RAR to low accelerations with data from galaxy-galaxy weak lensing, dwarf spheroidal galaxy stellar kinematic, and outer Milky Way dynamical measurements, fully independent of the uncertainties inherent in direct measurements of the baryonic matter distribution. In all cases we find that the data weakly favour a break to a steeper low- acceleration slope. Improvements in measurements and modelling of the outer Milky Way, and weak lensing, seem like the most promising path toward stronger constraints on the low-acceleration behaviour of the RAR.
@article{2020arXiv200606700O, author = {{Oman}, Kyle A. and {Brouwer}, Margot M. and {Ludlow}, Aaron D. and {Navarro}, Julio F.}, title = {{Observational constraints on the slope of the radial acceleration relation at low accelerations}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2020}, month = jun, eid = {arXiv:2006.06700}, pages = {arXiv:2006.06700}, doi = {10.48550/arXiv.2006.06700}, archiveprefix = {arXiv}, eprint = {2006.06700}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2020arXiv200606700O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Baryonic clues to the puzzling diversity of dwarf galaxy rotation curves

Isabel M. E. Santos-Santos, Julio F. Navarro, Andrew Robertson, and 7 more authors

(2020) MNRAS 495 58

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We use a compilation of disc galaxy rotation curves to assess the role of the luminous component (’baryons’) in the rotation curve diversity problem. As in earlier work, we find that rotation curve shape correlates with baryonic surface density: high surface density galaxies have rapidly rising rotation curves consistent with cuspy cold dark matter haloes; slowly rising rotation curves (characteristic of galaxies with inner mass deficits or ’cores’) occur only in low surface density galaxies. The correlation, however, seems too weak to be the main driver of the diversity. In addition, dwarf galaxies exhibit a clear trend, from ’cuspy’ systems where baryons are unimportant in the inner mass budget to ’cored’ galaxies where baryons actually dominate. This trend constrains the various scenarios proposed to explain the diversity, such as (I) baryonic inflows and outflows during galaxy formation; (II) dark matter self- interactions; (III) variations in the baryonic mass structure coupled to rotation velocities through the ’mass discrepancy- acceleration relation’ (MDAR); or (IV) non-circular motions in gaseous discs. Together with analytical modelling and cosmological hydrodynamical simulations, our analysis shows that each of these scenarios has promising features, but none seems to fully account for the observed diversity. The MDAR, in particular, is inconsistent with the observed trend between rotation curve shape and baryonic importance; either the trend is caused by systematic errors in the data or the MDAR does not apply. The origin of the dwarf galaxy rotation curve diversity and its relation to the structure of cold dark matter haloes remains an open issue.
@article{2020MNRAS.495...58S, author = {{Santos-Santos}, Isabel M. E. and {Navarro}, Julio F. and {Robertson}, Andrew and {Ben{\'\i}tez-Llambay}, Alejandro and {Oman}, Kyle A. and {Lovell}, Mark R. and {Frenk}, Carlos S. and {Ludlow}, Aaron D. and {Fattahi}, Azadeh and {Ritz}, Adam}, title = {{Baryonic clues to the puzzling diversity of dwarf galaxy rotation curves}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: evolution, galaxies: formation, galaxies: haloes, dark matter, cosmology: theory, Astrophysics - Astrophysics of Galaxies}, year = {2020}, month = jun, volume = {495}, number = {1}, pages = {58-77}, doi = {10.1093/mnras/staa1072}, archiveprefix = {arXiv}, eprint = {1911.09116}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2020MNRAS.495...58S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The milky way total mass profile as inferred from Gaia DR2

Marius Cautun, Alejandro Benı́tez-Llambay, Alis J. Deason, and 7 more authors

(2020) MNRAS 494 4291

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We determine the Milky Way (MW) mass profile inferred from fitting physically motivated models to the Gaia DR2 Galactic rotation curve and other data. Using various hydrodynamical simulations of MW-mass haloes, we show that the presence of baryons induces a contraction of the dark matter (DM) distribution in the inner regions, r ≲ 20 kpc. We provide an analytic expression that relates the baryonic distribution to the change in the DM halo profile. For our galaxy, the contraction increases the enclosed DM halo mass by factors of roughly 1.3, 2, and 4 at radial distances of 20, 8, and 1 kpc, respectively compared to an uncontracted halo. Ignoring this contraction results in systematic biases in the inferred halo mass and concentration. We provide a best-fitting contracted NFW halo model to the MW rotation curve that matches the data very well. The best-fit has a DM halo mass, M₂₀₀^DM=0.97_-0.19^+0.24 × 10¹² M_⊙, and concentration before baryon contraction of 9.4_-2.6^+1.9, which lie close to the median halo mass-concentration relation predicted in ΛCDM. The inferred total mass, M₂₀₀^total=1.08_-0.14^+0.20 × 10¹² M_⊙, is in good agreement with recent measurements. The model gives an MW stellar mass of 5.04_-0.52^+0.43 × 10¹⁰ M_⊙ and infers that the DM density at the Solar position is ρ_⊙^DM=8.8_-0.5^+0.5 × 10^-3 M_⊙ pc^-3 ≡ 0.33_-0.02^+0.02 GeV cm^-3. The rotation curve data can also be fitted with an uncontracted NFW halo model, but with very different DM and stellar parameters. The observations prefer the physically motivated contracted NFW halo, but the measurement uncertainties are too large to rule out the uncontracted NFW halo.
@article{2020MNRAS.494.4291C, author = {{Cautun}, Marius and {Ben{\'\i}tez-Llambay}, Alejandro and {Deason}, Alis J. and {Frenk}, Carlos S. and {Fattahi}, Azadeh and {G{\'o}mez}, Facundo A. and {Grand}, Robert J. J. and {Oman}, Kyle A. and {Navarro}, Julio F. and {Simpson}, Christine M.}, title = {{The milky way total mass profile as inferred from Gaia DR2}}, journal = {\mnras}, keywords = {Galaxy: fundamental parameters, Galaxy: halo, Galaxy: kinematics and dynamics, Galaxy: structure, galaxies: haloes, Astrophysics - Astrophysics of Galaxies}, year = {2020}, month = may, volume = {494}, number = {3}, pages = {4291-4313}, doi = {10.1093/mnras/staa1017}, archiveprefix = {arXiv}, eprint = {1911.04557}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2020MNRAS.494.4291C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Subhalo destruction in the APOSTLE and AURIGA simulations

Jack Richings, Carlos Frenk, Adrian Jenkins, and 8 more authors

(2020) MNRAS 492 5780

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N-body simulations make unambiguous predictions for the abundance of substructures within dark matter haloes. However, the inclusion of baryons in the simulations changes the picture because processes associated with the presence of a large galaxy in the halo can destroy subhaloes and substantially alter the mass function and velocity distribution of subhaloes. We compare the effect of galaxy formation on subhalo populations in two state- of-the-art sets of hydrodynamical Λcold dark matter (ΛCDM) simulations of Milky Way mass haloes, APOSTLE and AURIGA. We introduce a new method for tracking the orbits of subhaloes between simulation snapshots that gives accurate results down to a few kiloparsecs from the centre of the halo. Relative to a dark matter-only simulation, the abundance of subhaloes in APOSTLE is reduced by 50 per cent near the centre and by 10 per cent within r₂₀₀. In AURIGA, the corresponding numbers are 80 per cent and 40 per cent. The velocity distributions of subhaloes are also affected by the presence of the galaxy, much more so in AURIGA than in APOSTLE. The differences on subhalo properties in the two simulations can be traced back to the mass of the central galaxies, which in AURIGA are typically twice as massive as those in APOSTLE. We show that some of the results from previous studies are inaccurate due to systematic errors in the modelling of subhalo orbits near the centre of haloes.
@article{2020MNRAS.492.5780R, author = {{Richings}, Jack and {Frenk}, Carlos and {Jenkins}, Adrian and {Robertson}, Andrew and {Fattahi}, Azadeh and {Grand}, Robert J. J. and {Navarro}, Julio and {Pakmor}, R{\"u}diger and {Gomez}, Facundo A. and {Marinacci}, Federico and {Oman}, Kyle A.}, title = {{Subhalo destruction in the APOSTLE and AURIGA simulations}}, journal = {\mnras}, keywords = {methods: Numerical, galaxies: kinematics and dynamics, cosmology: theory, (cosmology:) dark matter, Astrophysics - Astrophysics of Galaxies}, year = {2020}, month = mar, volume = {492}, number = {4}, pages = {5780-5793}, doi = {10.1093/mnras/stz3448}, archiveprefix = {arXiv}, eprint = {1811.12437}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2020MNRAS.492.5780R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The Ophiuchus stream progenitor: a new type of globular cluster and its possible Sagittarius connection

James M. M. Lane, Julio F. Navarro, Azadeh Fattahi, and 2 more authors

(2020) MNRAS 492 4164

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The Ophiuchus stream is a short arc-like stellar feature of uncertain origin located ∼5 kpc North of the Galactic centre. New proper motions from the second Gaia data release reconcile the direction of motion of stream members with the stream arc, resolving a puzzling mismatch reported in earlier work. We use N-body simulations to show that the stream is likely only on its second pericentric passage, and thus was formed recently. The simulations suggest that most of the disrupted progenitor is visible in the observed stream today, and that little further tidal debris is expected to lie beyond the ends of the stream. The luminosity, length, width, and velocity dispersion of the stream suggest a globular cluster (GC) progenitor substantially fainter and of lower surface brightness than estimated in previous work, and unlike any other known globulars in the Galaxy. This result suggests the existence of clusters that would extend the known GC population to fainter and more weakly bound systems than hitherto known. How such a weakly bound cluster of old stars survived until it was disrupted so recently, however, remains a mystery. Integrating backwards in time, we find that the orbits of Sagittarius and Ophiuchus passed within ∼5 kpc of each other about ∼100 Myr ago, an interaction that might help resolve this puzzle.
@article{2020MNRAS.492.4164L, author = {{Lane}, James M. M. and {Navarro}, Julio F. and {Fattahi}, Azadeh and {Oman}, Kyle A. and {Bovy}, Jo}, title = {{The Ophiuchus stream progenitor: a new type of globular cluster and its possible Sagittarius connection}}, journal = {\mnras}, keywords = {Galaxy: evolution, globular clusters: general, Galaxy: halo, Galaxy: kinematics and dynamics, Galaxy: structure, galaxies: dwarf, Astrophysics - Astrophysics of Galaxies}, year = {2020}, month = mar, volume = {492}, number = {3}, pages = {4164-4174}, doi = {10.1093/mnras/staa095}, archiveprefix = {arXiv}, eprint = {1905.12633}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2020MNRAS.492.4164L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2019

The HI velocity function: a test of cosmology or baryon physics?

Garima Chauhan, Claudia del P. Lagos, Danail Obreschkow, and 3 more authors

(2019) MNRAS 488 5898

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Accurately predicting the shape of the HI velocity function (VF) of galaxies is regarded widely as a fundamental test of any viable dark matter model. Straightforward analyses of cosmological N-body simulations imply that the Λ cold dark matter (ΛCDM) model predicts an overabundance of low circular velocity galaxies when compared to observed HI VFs. More nuanced analyses that account for the relationship between galaxies and their host haloes suggest that how we model the influence of baryonic processes has a significant impact on HI VF predictions. We explore this in detail by modelling HI emission lines of galaxies in the SHARK semi-analytic galaxy formation model, built on the SURFS suite of ΛCDM N-body simulations. We create a simulated ALFALFA survey, in which we apply the survey selection function and account for effects such as beam confusion, and compare simulated and observed HI velocity width distributions, finding differences of ≲ 50 per cent, orders of magnitude smaller than the discrepancies reported in the past. This is a direct consequence of our careful treatment of survey selection effects and, importantly, how we model the relationship between galaxy and halo circular velocity - the HI mass-maximum circular velocity relation of galaxies is characterized by a large scatter. These biases are complex enough that building a VF from the observed HI linewidths cannot be done reliably.
@article{2019MNRAS.488.5898C, author = {{Chauhan}, Garima and {Lagos}, Claudia del P. and {Obreschkow}, Danail and {Power}, Chris and {Oman}, Kyle and {Elahi}, Pascal J.}, title = {{The HI velocity function: a test of cosmology or baryon physics?}}, journal = {\mnras}, keywords = {galaxies: evolution, galaxies: formation, galaxies: kinematics and dynamics, Astrophysics - Astrophysics of Galaxies}, year = {2019}, month = oct, volume = {488}, number = {4}, pages = {5898-5915}, doi = {10.1093/mnras/stz2069}, archiveprefix = {arXiv}, eprint = {1906.06130}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2019MNRAS.488.5898C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

Off the Baryonic Tully-Fisher Relation: A Population of Baryon-dominated Ultra-diffuse Galaxies

Pavel E. Mancera Piña, Filippo Fraternali, Elizabeth A. K. Adams, and 17 more authors

(2019) ApJL 883 L33

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We study the gas kinematics traced by the 21 cm emission of a sample of six HI-rich low surface brightness galaxies classified as ultra-diffuse galaxies (UDGs). Using the 3D kinematic modeling code ^3DBarolo we derive robust circular velocities, revealing a startling feature: HI-rich UDGs are clear outliers from the baryonic Tully-Fisher relation, with circular velocities much lower than galaxies with similar baryonic mass. Notably, the baryon fraction of our UDG sample is consistent with the cosmological value: these UDGs are compatible with having no ’missing baryons’ within their virial radii. Moreover, the gravitational potential provided by the baryons is sufficient to account for the amplitude of the rotation curve out to the outermost measured point, contrary to other galaxies with similar circular velocities. We speculate that any formation scenario for these objects will require very inefficient feedback and a broad diversity in their inner dark matter content.

@article{2019ApJ...883L..33M,
  author = {{Mancera Pi{\~n}a}, Pavel E. and {Fraternali}, Filippo and {Adams}, Elizabeth A. K. and {Marasco}, Antonino and {Oosterloo}, Tom and {Oman}, Kyle A. and {Leisman}, Lukas and {di Teodoro}, Enrico M. and {Posti}, Lorenzo and {Battipaglia}, Michael and {Cannon}, John M. and {Gault}, Lexi and {Haynes}, Martha P. and {Janowiecki}, Steven and {McAllan}, Elizabeth and {Pagel}, Hannah J. and {Reiter}, Kameron and {Rhode}, Katherine L. and {Salzer}, John J. and {Smith}, Nicholas J.},
  title = {{Off the Baryonic Tully-Fisher Relation: A Population of Baryon-dominated Ultra-diffuse Galaxies}},
  journal = {\apjl},
  keywords = {Dwarf galaxies, Galaxy formation, Galaxy evolution, Galaxy kinematics, Galaxy dynamics, Dark matter, Low surface brightness galaxies, Galaxy rotation curves, 416, 595, 594, 602, 591, 353, 940, 619, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics},
  year = {2019},
  month = oct,
  volume = {883},
  number = {2},
  eid = {L33},
  pages = {L33},
  doi = {10.3847/2041-8213/ab40c7},
  archiveprefix = {arXiv},
  eprint = {1909.01363},
  primaryclass = {astro-ph.GA},
  adsurl = {https://ui.adsabs.harvard.edu/abs/2019ApJ...883L..33M},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System},
}

The distinct stellar metallicity populations of simulated Local Group dwarfs

Anna Genina, Carlos S. Frenk, Alejandro Benı́tez-Llambay, and 4 more authors

(2019) MNRAS 488 2312

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A number of Local Group dwarf galaxies are known to have two spatially segregated stellar metallicity populations, a centrally concentrated metal-rich population, and a more extended metal- poor population. In this work we discuss mechanisms that lead to the formation of two spatially segregated metallicity populations. Using a set of high-resolution hydrodynamical simulations of Local Group-like environments, we select a sample of satellite and field galaxies, spanning the stellar mass range 10⁶-10⁹ M_⊙, that exhibit bimodality in their metallicity distributions. Among those, we identify a subsample with a strong spatial segregation in the two populations. We find three distinct mechanisms for their formation. In field dwarfs and in a small fraction of satellites, a merger causes the metal-poor stars to migrate to larger radii and encourages the available gas to sink to the centre of the dwarf. Most of the gas is subsequently blown out of the halo through star formation feedback, but the remaining gas is consumed in the formation of a metal-rich population. In the exclusive case of satellites that have retained some of their gas at infall, it is the compression of this gas by ram pressure near pericentre that triggers the formation of metal- rich stars, whilst simultaneously preventing star formation at larger radii through stripping. Additionally, in a small number of field and satellite dwarfs, interactions with gaseous filaments and other galaxies can result in the formation of a metal-rich population. Regardless of the formation mechanism, a history of mergers typically enhances the spatial segregation.
@article{2019MNRAS.488.2312G, author = {{Genina}, Anna and {Frenk}, Carlos S. and {Ben{\'\i}tez-Llambay}, Alejandro and {Cole}, Shaun and {Navarro}, Julio F. and {Oman}, Kyle A. and {Fattahi}, Azadeh}, title = {{The distinct stellar metallicity populations of simulated Local Group dwarfs}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: evolution, galaxies: formation, galaxies: interactions, Local Group, Astrophysics - Astrophysics of Galaxies}, year = {2019}, month = sep, volume = {488}, number = {2}, pages = {2312-2331}, doi = {10.1093/mnras/stz1852}, archiveprefix = {arXiv}, eprint = {1812.04839}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2019MNRAS.488.2312G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
No cores in dark matter-dominated dwarf galaxies with bursty star formation histories

Sownak Bose, Carlos S. Frenk, Adrian Jenkins, and 10 more authors

(2019) MNRAS 486 4790

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Measurements of the rotation curves of dwarf galaxies are often interpreted as requiring a constant density core at the centre, at odds with the ‘cuspy’ inner profiles predicted by N-body simulations of cold dark matter (CDM) haloes. It has been suggested that this conflict could be resolved by fluctuations in the inner gravitational potential caused by the periodic removal of gas following bursts of star formation. Earlier work has suggested that core formation requires a bursty and extended star formation history (SFH). Here we investigate the structure of CDM haloes of dwarf galaxies (M_DM ∼10⁹-5× 10¹⁰ M_⊙) formed in the APOSTLE (‘A Project of Simulating the Local Environment’) and AURIGA cosmological hydrodynamic simulations. Our simulations have comparable or better resolution than others that make cores (M_gas ∼10⁴ M_⊙, gravitational softening ∼150 pc). Yet, we do not find evidence of core formation at any mass or any correlation between the inner slope of the DM density profile and temporal variations in the SFH. APOSTLE and AURIGA dwarfs display a similar diversity in their cumulative SFHs to available data for Local Group dwarfs. Dwarfs in both simulations are DM-dominated on all resolved scales at all times, likely limiting the ability of gas outflows to alter significantly the central density profiles of their haloes. We conclude that recurrent bursts of star formation are not sufficient to cause the formation of cores, and that other conditions must also be met for baryons to be able to modify the central DM cusp.
@article{2019MNRAS.486.4790B, author = {{Bose}, Sownak and {Frenk}, Carlos S. and {Jenkins}, Adrian and {Fattahi}, Azadeh and {G{\'o}mez}, Facundo A. and {Grand}, Robert J. J. and {Marinacci}, Federico and {Navarro}, Julio F. and {Oman}, Kyle A. and {Pakmor}, R{\"u}diger and {Schaye}, Joop and {Simpson}, Christine M. and {Springel}, Volker}, title = {{No cores in dark matter-dominated dwarf galaxies with bursty star formation histories}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: haloes, Local Group, galaxies: star formation, dark matter, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2019}, month = jul, volume = {486}, number = {4}, pages = {4790-4804}, doi = {10.1093/mnras/stz1168}, archiveprefix = {arXiv}, eprint = {1810.03635}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2019MNRAS.486.4790B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The star formation histories of dwarf galaxies in Local Group cosmological simulations

Ruth Digby, Julio F. Navarro, Azadeh Fattahi, and 6 more authors

(2019) MNRAS 485 5423

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We use the APOSTLE and Auriga cosmological simulations to study the star formation histories (SFHs) of field and satellite dwarf galaxies. Despite sizeable galaxy-to-galaxy scatter, the SFHs of APOSTLE and Auriga dwarfs exhibit robust average trends with galaxy stellar mass: faint field dwarfs (10⁵ < M_★/M_⊙ < 10⁶) have, on average, steadily declining SFHs, whereas brighter dwarfs (10⁷ < M_★/M_⊙ < 10⁹) show the opposite trend. Intermediate-mass dwarfs have roughly constant SFHs. Satellites exhibit similar average trends, but with substantially suppressed star formation in the most recent ∼5 Gyr, likely as a result of gas loss due to tidal and ram-pressure stripping after entering the haloes of their primaries. These simple mass and environmental trends are in good agreement with the derived SFHs of Local Group (LG) dwarfs whose photometry reaches the oldest main- sequence turn-off. SFHs of galaxies with less deep data show deviations from these trends, but this may be explained, at least in part, by the large galaxy-to-galaxy scatter, the limited sample size, and the large uncertainties of the inferred SFHs. Confirming the predicted mass and environmental trends will require deeper photometric data than currently available, especially for isolated dwarfs.
@article{2019MNRAS.485.5423D, author = {{Digby}, Ruth and {Navarro}, Julio F. and {Fattahi}, Azadeh and {Simpson}, Christine M. and {Oman}, Kyle A. and {Gomez}, Facundo A. and {Frenk}, Carlos S. and {Grand}, Robert J. J. and {Pakmor}, Ruediger}, title = {{The star formation histories of dwarf galaxies in Local Group cosmological simulations}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: evolution, Local Group, galaxies: star formation, Astrophysics - Astrophysics of Galaxies}, year = {2019}, month = jun, volume = {485}, number = {4}, pages = {5423-5437}, doi = {10.1093/mnras/stz745}, archiveprefix = {arXiv}, eprint = {1812.05669}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2019MNRAS.485.5423D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The SAMI Galaxy Survey: Quenching of Star Formation in Clusters I. Transition Galaxies

Matt S. Owers, Michael J. Hudson, Kyle A. Oman, and 19 more authors

(2019) ApJ 873 52

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We use integral-field spectroscopy from the SAMI Galaxy Survey to identify galaxies that show evidence of recent quenching of star formation. The galaxies exhibit strong Balmer absorption in the absence of ongoing star formation in more than 10% of their spectra within the SAMI field of view. These Hδ-strong (HDS) galaxies (HDSGs) are rare, making up only ∼2% (25/1220) of galaxies with stellar mass log(M_★/M_⊙) > 10. The HDSGs make up a significant fraction of nonpassive cluster galaxies (15%; 17/115) and a smaller fraction (2.0%; 8/387) of the nonpassive population in low-density environments. The majority (9/17) of cluster HDSGs show evidence of star formation at their centers, with the HDS regions found in the outer parts of the galaxy. Conversely, the HDS signal is more evenly spread across the galaxy for the majority (6/8) of HDSGs in low-density environments and is often associated with emission lines that are not due to star formation. We investigate the location of the HDSGs in the clusters, finding that they are exclusively within 0.6R ₂₀₀ of the cluster center and have a significantly higher velocity dispersion relative to the cluster population. Comparing their distribution in projected phase space to those derived from cosmological simulations indicates that the cluster HDSGs are consistent with an infalling population that has entered the central 0.5r_200,3D cluster region within the last ∼1 Gyr. In the eight of nine cluster HDSGs with central star formation, the extent of star formation is consistent with that expected of outside-in quenching by ram pressure stripping. Our results indicate that the cluster HDSGs are currently being quenched by ram pressure stripping on their first passage through the cluster.
@article{2019ApJ...873...52O, author = {{Owers}, Matt S. and {Hudson}, Michael J. and {Oman}, Kyle A. and {Bland-Hawthorn}, Joss and {Brough}, S. and {Bryant}, Julia J. and {Cortese}, Luca and {Couch}, Warrick J. and {Croom}, Scott M. and {van de Sande}, Jesse and {Federrath}, Christoph and {Groves}, Brent and {Hopkins}, A. M. and {Lawrence}, J. S. and {Lorente}, Nuria P. F. and {McDermid}, Richard M. and {Medling}, Anne M. and {Richards}, Samuel N. and {Scott}, Nicholas and {Taranu}, Dan S. and {Welker}, Charlotte and {Yi}, Sukyoung K.}, title = {{The SAMI Galaxy Survey: Quenching of Star Formation in Clusters I. Transition Galaxies}}, journal = {\apj}, keywords = {galaxies: clusters: general, galaxies: evolution, galaxies: star formation, Astrophysics - Astrophysics of Galaxies}, year = {2019}, month = mar, volume = {873}, number = {1}, eid = {52}, pages = {52}, doi = {10.3847/1538-4357/ab0201}, archiveprefix = {arXiv}, eprint = {1901.08185}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2019ApJ...873...52O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Non-circular motions and the diversity of dwarf galaxy rotation curves

Kyle A. Oman, Antonino Marasco, Julio F. Navarro, and 3 more authors

(2019) MNRAS 482 821

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We use mock interferometric HI measurements and a conventional tilted- ring modelling procedure to estimate circular velocity curves of dwarf galaxy discs from the APOSTLE suite of Λ cold dark matter cosmological hydrodynamical simulations. The modelling yields a large diversity of rotation curves for an individual galaxy at fixed inclination, depending on the line-of-sight orientation. The diversity is driven by non-circular motions in the gas; in particular, by strong bisymmetric fluctuations in the azimuthal velocities that the tilted-ring model is ill-suited to account for and that are difficult to detect in model residuals. Large misestimates of the circular velocity arise when the kinematic major axis coincides with the extrema of the fluctuation pattern, in some cases mimicking the presence of kiloparsec- scale density ‘cores’, when none are actually present. The thickness of APOSTLE discs compounds this effect: more slowly rotating extra-planar gas systematically reduces the average line-of-sight speeds. The recovered rotation curves thus tend to underestimate the true circular velocity of APOSTLE galaxies in the inner regions. Non-circular motions provide an appealing explanation for the large apparent cores observed in galaxies such as DDO 47 and DDO 87, where the model residuals suggest that such motions might have affected estimates of the inner circular velocities. Although residuals from tilted-ring models in the simulations appear larger than in observed galaxies, our results suggest that non-circular motions should be carefully taken into account when considering the evidence for dark matter cores in individual galaxies.
@article{2019MNRAS.482..821O, author = {{Oman}, Kyle A. and {Marasco}, Antonino and {Navarro}, Julio F. and {Frenk}, Carlos S. and {Schaye}, Joop and {Ben{\'\i}tez-Llambay}, Alejandro}, title = {{Non-circular motions and the diversity of dwarf galaxy rotation curves}}, journal = {\mnras}, keywords = {ISM: kinematics and dynamics, galaxies: haloes, galaxies: structure, dark matter, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2019}, month = jan, volume = {482}, number = {1}, pages = {821-847}, doi = {10.1093/mnras/sty2687}, archiveprefix = {arXiv}, eprint = {1706.07478}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2019MNRAS.482..821O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2018

The APOSTLE simulations: Rotation curves derived from synthetic 21-cm observations

Kyle A. Oman

Eds. Cristina Chiappini, Ivan Minchev, Else Starkenburg, and 1 more editor

(2018) In Rediscovering Our Galaxy, IAUS 334 213

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The apostle cosmological hydrodynamical simulation suite is a collection of twelve regions ∼5 Mpc in diameter, selected to resemble the Local Group of galaxies in terms of kinematics and environment, and re-simulated at high resolution (minimum gas particle mass of 10⁴ M_⊙) using the galaxy formation model and calibration developed for the eagle project. I select a sample of dwarf galaxies (60 < V_max/km s^-1 < 120) from these simulations and construct synthetic spatially- and spectrally- resolved observations of their 21-cm emission. Using the ^3DBarolo tilted-ring modelling tool, I extract rotation curves from the synthetic data cubes. In many cases, non- circular motions present in the gas disc hinder the recovery of a rotation curve which accurately traces the underlying mass distribution; a large central deficit of dark matter, relative to the predictions of cold dark matter N-body simulations, may then be erroneously inferred.
@inproceedings{2018IAUS..334..213O, author = {{Oman}, Kyle A.}, title = {{The APOSTLE simulations: Rotation curves derived from synthetic 21-cm observations}}, keywords = {Galaxies: halos, galaxies: kinematics and dynamics, dark matter, Astrophysics - Astrophysics of Galaxies}, booktitle = {Rediscovering Our Galaxy}, journal = {IAUS}, year = {2018}, editor = {{Chiappini}, Cristina and {Minchev}, Ivan and {Starkenburg}, Else and {Valentini}, Marica}, volume = {334}, month = aug, pages = {213-218}, doi = {10.1017/S1743921317006615}, archiveprefix = {arXiv}, eprint = {1712.02562}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2018IAUS..334..213O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Bars in dark-matter-dominated dwarf galaxy discs

A. Marasco, K. A. Oman, J. F. Navarro, and 2 more authors

(2018) MNRAS 476 2168

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We study the shape and kinematics of simulated dwarf galaxy discs in the APOSTLE suite of Λ cold dark matter (ΛCDM) cosmological hydrodynamical simulations. We find that a large fraction of these gas-rich, star-forming discs show weak bars in their stellar component, despite being dark-matter-dominated systems. The bar pattern shape and orientation reflect the ellipticity of the dark matter potential, and its rotation is locked to the slow figure rotation of the triaxial dark halo. The bar-like nature of the potential induces non-circular motions in the gas component, including strong bisymmetric flows that can be readily seen as m = 3 harmonic perturbations in the HI line-of-sight velocity fields. Similar bisymmetric flows are seen in many galaxies of The HI Nearby Galaxy Survey (THINGS) and Local Irregulars That Trace Luminosity Extremes THINGS (LITTLE THINGS), although on average their amplitudes are a factor of ∼2 weaker than in our simulated discs. Our results indicate that bar-like patterns may arise even when baryons are not dominant, and that they are common enough to warrant careful consideration when analysing the gas kinematics of dwarf galaxy discs.
@article{2018MNRAS.476.2168M, author = {{Marasco}, A. and {Oman}, K. A. and {Navarro}, J. F. and {Frenk}, C. S. and {Oosterloo}, T.}, title = {{Bars in dark-matter-dominated dwarf galaxy discs}}, journal = {\mnras}, keywords = {ISM: kinematics and dynamics, galaxies: dwarf, galaxies: kinematics and dynamics, galaxies: structure, dark matter, Astrophysics - Astrophysics of Galaxies}, year = {2018}, month = may, volume = {476}, number = {2}, pages = {2168-2176}, doi = {10.1093/mnras/sty354}, archiveprefix = {arXiv}, eprint = {1711.09914}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2018MNRAS.476.2168M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Tidal stripping and the structure of dwarf galaxies in the Local Group

Azadeh Fattahi, Julio F. Navarro, Carlos S. Frenk, and 3 more authors

(2018) MNRAS 476 3816

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The shallow faint-end slope of the galaxy mass function is usually reproduced in Λ cold dark matter (ΛCDM) galaxy formation models by assuming that the fraction of baryons that turn into stars drops steeply with decreasing halo mass and essentially vanishes in haloes with maximum circular velocities V_max < 20-30 km s^-1. Dark-matter-dominated dwarfs should therefore have characteristic velocities of about that value, unless they are small enough to probe only the rising part of the halo circular velocity curve (i.e. half-mass radii, r_1/2 ≪ 1 kpc). Many dwarfs have properties in disagreement with this prediction: they are large enough to probe their halo V_max but their characteristic velocities are well below 20 km s^-1. These ’cold faint giants’ (an extreme example is the recently discovered Crater 2 Milky Way satellite) can only be reconciled with our ΛCDM models if they are the remnants of once massive objects heavily affected by tidal stripping. We examine this possibility using the APOSTLE cosmological hydrodynamical simulations of the Local Group. Assuming that low-velocity-dispersion satellites have been affected by stripping, we infer their progenitor masses, radii, and velocity dispersions, and find them in remarkable agreement with those of isolated dwarfs. Tidal stripping also explains the large scatter in the mass discrepancy-acceleration relation in the dwarf galaxy regime: tides remove preferentially dark matter from satellite galaxies, lowering their accelerations below the a_min ∼10^-11 m s^-2 minimum expected for isolated dwarfs. In many cases, the resulting velocity dispersions are inconsistent with the predictions from Modified Newtonian Dynamics, a result that poses a possibly insurmountable challenge to that scenario.
@article{2018MNRAS.476.3816F, author = {{Fattahi}, Azadeh and {Navarro}, Julio F. and {Frenk}, Carlos S. and {Oman}, Kyle A. and {Sawala}, Till and {Schaller}, Matthieu}, title = {{Tidal stripping and the structure of dwarf galaxies in the Local Group}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: evolution, galaxies: kinematics and dynamics, Local Group, dark matter, Astrophysics - Astrophysics of Galaxies}, year = {2018}, month = may, volume = {476}, number = {3}, pages = {3816-3836}, doi = {10.1093/mnras/sty408}, archiveprefix = {arXiv}, eprint = {1707.03898}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2018MNRAS.476.3816F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The innate origin of radial and vertical gradients in a simulated galaxy disc

Julio F. Navarro, Cameron Yozin, Nic Loewen, and 6 more authors

(2018) MNRAS 476 3648

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We examine the origin of radial and vertical gradients in the age/metallicity of the stellar component of a galaxy disc formed in the APOSTLE cosmological hydrodynamical simulations. Some of these gradients resemble those in the Milky Way, where they have sometimes been interpreted as due to internal evolution, such as scattering off giant molecular clouds, radial migration driven by spiral patterns, or orbital resonances with a bar. Secular processes play a minor role in the simulated galaxy, which lacks strong spiral or bar patterns, and where such gradients arise as a result of the gradual enrichment of a gaseous disc that is born thick but thins as it turns into stars and settles into centrifugal equilibrium. The settling is controlled by the feedback of young stars; which links the star formation, enrichment, and equilibration time-scales, inducing radial and vertical gradients in the gaseous disc and its descendent stars. The kinematics of coeval stars evolve little after birth and provide a faithful snapshot of the gaseous disc structure at the time of their formation. In this interpretation, the age- velocity dispersion relation would reflect the gradual thinning of the disc rather than the importance of secular orbit scattering; the outward flaring of stars would result from the gas disc flare rather than from radial migration; and vertical gradients would arise because the gas disc gradually thinned as it enriched. Such radial and vertical trends might just reflect the evolving properties of the parent gaseous disc, and are not necessarily the result of secular evolutionary processes.
@article{2018MNRAS.476.3648N, author = {{Navarro}, Julio F. and {Yozin}, Cameron and {Loewen}, Nic and {Ben{\'\i}tez-Llambay}, Alejandro and {Fattahi}, Azadeh and {Frenk}, Carlos S. and {Oman}, Kyle A. and {Schaye}, Joop and {Theuns}, Tom}, title = {{The innate origin of radial and vertical gradients in a simulated galaxy disc}}, journal = {\mnras}, keywords = {galaxies: evolution, galaxies: formation, galaxies: kinematics and dynamics, galaxies: structure, Astrophysics - Astrophysics of Galaxies}, year = {2018}, month = may, volume = {476}, number = {3}, pages = {3648-3660}, doi = {10.1093/mnras/sty497}, archiveprefix = {arXiv}, eprint = {1709.01040}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2018MNRAS.476.3648N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The core-cusp problem: a matter of perspective

Anna Genina, Alejandro Benı́tez-Llambay, Carlos S. Frenk, and 6 more authors

(2018) MNRAS 474 1398

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The existence of two kinematically and chemically distinct stellar subpopulations in the Sculptor and Fornax dwarf galaxies offers the opportunity to constrain the density profile of their matter haloes by measuring the mass contained within the well-separated half-light radii of the two metallicity subpopulations. Walker and Peñarrubia have used this approach to argue that data for these galaxies are consistent with constant-density ‘cores’ in their inner regions and rule out ‘cuspy’ Navarro-Frenk-White (NFW) profiles with high statistical significance, particularly in the case of Sculptor. We test the validity of these claims using dwarf galaxies in the APOSTLE (A Project Of Simulating The Local Environment) Λ cold dark matter cosmological hydrodynamic simulations of analogues of the Local Group. These galaxies all have NFW dark matter density profiles and a subset of them develop two distinct metallicity subpopulations reminiscent of Sculptor and Fornax. We apply a method analogous to that of Walker and Peñarrubia to a sample of 50 simulated dwarfs and find that this procedure often leads to a statistically significant detection of a core in the profile when in reality there is a cusp. Although multiple factors contribute to these failures, the main cause is a violation of the assumption of spherical symmetry upon which the mass estimators are based. The stellar populations of the simulated dwarfs tend to be significantly elongated and, in several cases, the two metallicity populations have different asphericity and are misaligned. As a result, a wide range of slopes of the density profile are inferred depending on the angle from which the galaxy is viewed.
@article{2018MNRAS.474.1398G, author = {{Genina}, Anna and {Ben{\'\i}tez-Llambay}, Alejandro and {Frenk}, Carlos S. and {Cole}, Shaun and {Fattahi}, Azadeh and {Navarro}, Julio F. and {Oman}, Kyle A. and {Sawala}, Till and {Theuns}, Tom}, title = {{The core-cusp problem: a matter of perspective}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: formation, galaxies: kinematics and dynamics, dark matter, Astrophysics - Astrophysics of Galaxies}, year = {2018}, month = feb, volume = {474}, number = {1}, pages = {1398-1411}, doi = {10.1093/mnras/stx2855}, archiveprefix = {arXiv}, eprint = {1707.06303}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2018MNRAS.474.1398G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2017

The origin of the mass discrepancy-acceleration relation in ΛCDM

Julio F. Navarro, Alejandro Benı́tez-Llambay, Azadeh Fattahi, and 5 more authors

(2017) MNRAS 471 1841

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We examine the origin of the mass discrepancy-radial acceleration relation (MDAR) of disc galaxies. This is a tight empirical correlation between the disc centripetal acceleration and that expected from the baryonic component. The MDAR holds for most radii probed by disc kinematic tracers, regardless of galaxy mass or surface brightness. The relation has two characteristic accelerations: a₀, above which all galaxies are baryon dominated, and a_min, an effective minimum acceleration probed by kinematic tracers in isolated galaxies. We use a simple model to show that these trends arise naturally in Λ cold dark matter (ΛCDM). This is because (I) disc galaxies in ΛCDM form at the centre of dark matter haloes spanning a relatively narrow range of virial mass; (II) cold dark matter halo acceleration profiles are self-similar and have a broad maximum at the centre, reaching values bracketed precisely by a_min and a₀ in that mass range and (III) halo mass and galaxy size scale relatively tightly with the baryonic mass of a galaxy in any successful ΛCDM galaxy formation model. Explaining the MDAR in ΛCDM does not require modifications to the cuspy inner mass profiles of dark haloes, although these may help to understand the detailed rotation curves of some dwarf galaxies and the origin of extreme outliers from the main relation. The MDAR is just a reflection of the self-similar nature of cold dark matter haloes and of the physical scales introduced by the galaxy formation process.
@article{2017MNRAS.471.1841N, author = {{Navarro}, Julio F. and {Ben{\'\i}tez-Llambay}, Alejandro and {Fattahi}, Azadeh and {Frenk}, Carlos S. and {Ludlow}, Aaron D. and {Oman}, Kyle A. and {Schaller}, Matthieu and {Theuns}, Tom}, title = {{The origin of the mass discrepancy-acceleration relation in ΛCDM}}, journal = {\mnras}, keywords = {galaxies: formation, galaxies: fundamental parameters, galaxies: kinematics and dynamics, galaxies: structure, dark matter, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2017}, month = oct, volume = {471}, number = {2}, pages = {1841-1848}, doi = {10.1093/mnras/stx1705}, archiveprefix = {arXiv}, eprint = {1612.06329}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2017MNRAS.471.1841N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The “Building Blocks” of Stellar Halos

Kyle Oman, Else Starkenburg, and Julio Navarro

(2017) Galaxies 5 33

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The stellar halos of galaxies encode their accretion histories. In particular, the median metallicity of a halo is determined primarily by the mass of the most massive accreted object. We use hydrodynamical cosmological simulations from the APOSTLE project to study the connection between the stellar mass, the metallicity distribution, and the stellar age distribution of a halo and the identity of its most massive progenitor. We find that the stellar populations in an accreted halo typically resemble the old stellar populations in a present-day dwarf galaxy with a stellar mass ∼0.2-0.5 dex greater than that of the stellar halo. This suggests that had they not been accreted, the primary progenitors of stellar halos would have evolved to resemble typical nearby dwarf irregulars.
@article{2017Galax...5...33O, author = {{Oman}, Kyle and {Starkenburg}, Else and {Navarro}, Julio}, title = {{The ``Building Blocks'' of Stellar Halos}}, journal = {Galaxies}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2017}, month = aug, volume = {5}, number = {3}, pages = {33}, doi = {10.3390/galaxies5030033}, archiveprefix = {arXiv}, eprint = {1708.00929}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2017Galax...5...33O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
An explanation for the unexpected diversity of dwarf galaxy rotation curves

Kyle A. Oman

(2017) PhD Thesis, University of Victoria

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The cosmological constant + cold dark matter (ΛCDM) theory is the ’standard model’ of cosmology. Encoded in it are extremely accurate descriptions of the large scale structure of the Universe, despite a very limited number of degrees of freedom. The model struggles, however, to explain some measurements on galactic and smaller scales. The shape of the dark matter distribution toward the centres of galaxies is predicted to be steeply increasing in density (’cuspy’) by the theory, yet observations of the rotation curves of some galaxies suggest that it instead reaches a central density plateau (a ’core’). This discrepancy is termed the ’cusp-core problem’. I propose a new way of quantifying this problem as a diversity in the central mass content of galaxies. This characterization does not distinguish between dark and ordinary (’baryonic’) matter, but the apparent problem is so severe that the signature of the cusp-core discrepancy is still obvious. By formulating the problem in this way, several uncertain modelling steps are effectively removed from the discussion, allowing for a more narrowly focussed examination of remaining steps in the analysis. My subsequent comparison of recent results from galaxy formation simulations and observed galaxies in the space of the baryonic Tully-Fisher relation (BTFR) reveals some galaxies with an apparent anomalously low dark matter content not only in the centre, but out to the largest measurable radii. These objects are very difficult to explain within the ΛCDM framework; the most plausible interpretation which emerges is that the effect of systematic uncertainties in modelling the kinematics in these galaxies – particularly in the estimate of their inclinations – has been substantially underestimated. This motivates a re-examination of rotation curve measurement methods. I use a collection of simulated galaxies to demonstrate that, when these are synthetically ’observed’ and modelled analogously to real galaxies, non-circular motions present in the gas discs give the appearance of cores, even though all of the simulated galaxies have central cusps. The errors are large enough to reproduce the full width of the observed scatter in rotation curve shapes. Provided the simulations produce sufficiently faithful models of real galaxies, these modelling errors could constitute a solution to the cusp-core problem within the ΛCDM paradigm. Regardless, the kinematic models must be better understood before drawing any strong cosmological conclusions.
@phdthesis{2017PhDT........80O, author = {{Oman}, Kyle A.}, title = {{An explanation for the unexpected diversity of dwarf galaxy rotation curves}}, keywords = {astrophysics, cosmology, galaxies, dark matter}, school = {University of Victoria, Department of Physics and Astronomy}, year = {2017}, month = aug, doi = {1828/8425}, adsurl = {https://ui.adsabs.harvard.edu/abs/2017PhDT........80O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Knowing the unknowns: uncertainties in simple estimators of galactic dynamical masses

David J. R. Campbell, Carlos S. Frenk, Adrian Jenkins, and 7 more authors

(2017) MNRAS 469 2335

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The observed stellar kinematics of dispersion-supported galaxies are often used to measure dynamical masses. Recently, several analytical relationships between the stellar line-of-sight velocity dispersion, the projected (2D) or deprojected (3D) half-light radius and the total mass enclosed within the half- light radius, relying on the spherical Jeans equation, have been proposed. Here, we use the APOSTLE cosmological hydrodynamical simulations of the Local Group to test the validity and accuracy of such mass estimators for both dispersion and rotation- supported galaxies, for field and satellite galaxies, and for galaxies of varying masses, shapes and velocity dispersion anisotropies. We find that the mass estimators of Walker et al. and Wolf et al. are able to recover the masses of dispersion- dominated systems with little systematic bias, but with a 1σ scatter of 25 and 23 per cent, respectively. The error on the estimated mass is dominated by the impact of the 3D shape of the stellar mass distribution, which is difficult to constrain observationally. This intrinsic scatter becomes the dominant source of uncertainty in the masses estimated for galaxies like the dwarf spheroidal (dSph) satellites of the Milky Way, where the observational errors in their sizes and velocity dispersions are small. Such scatter may also affect the inner density slopes of dSphs derived from multiple stellar populations, relaxing the significance with which Navarro-Frenk-White profiles may be excluded, depending on the degree to which the relevant properties of the different stellar populations are correlated. Finally, we derive a new optimal mass estimator that removes the residual biases and achieves a statistically significant reduction in the scatter to 20 per cent overall for dispersion-dominated galaxies, allowing more precise and accurate mass estimates.
@article{2017MNRAS.469.2335C, author = {{Campbell}, David J. R. and {Frenk}, Carlos S. and {Jenkins}, Adrian and {Eke}, Vincent R. and {Navarro}, Julio F. and {Sawala}, Till and {Schaller}, Matthieu and {Fattahi}, Azadeh and {Oman}, Kyle A. and {Theuns}, Tom}, title = {{Knowing the unknowns: uncertainties in simple estimators of galactic dynamical masses}}, journal = {\mnras}, keywords = {galaxies: dwarf, galaxies: formation, galaxies: fundamental parameters, galaxies: kinematics and dynamics, dark matter, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2017}, month = aug, volume = {469}, number = {2}, pages = {2335-2360}, doi = {10.1093/mnras/stx975}, archiveprefix = {arXiv}, eprint = {1603.04443}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2017MNRAS.469.2335C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Tidal features of classical Milky Way satellites in a Λ cold dark matter universe

M. -Y. Wang, Azadeh Fattahi, Andrew P. Cooper, and 6 more authors

(2017) MNRAS 468 4887

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We use the APOSTLE (A Project Of Simulating The Local Environment) cosmological hydrodynamic simulations to examine the effects of tidal stripping on cold dark matter subhaloes that host three of the most luminous Milky Way dwarf satellite galaxies: Fornax, Sculptor and Leo I. We identify simulated satellites that match the observed spatial and kinematic distributions of stars in these galaxies, and track their evolution after infall. We find ∼30 per cent of subhaloes hosting satellites with present-day stellar mass 10⁶-10⁸ M_⊙ experience >20 per cent stellar mass- loss after infall. Fornax analogues have earlier infall times compared to Sculptor and Leo I analogues. Star formation in Fornax analogues continues for ∼3-6 Gyr after infall, whereas Sculptor and Leo I analogues stop forming stars <2-3 Gyr after infall. Fornax analogues typically show more significant stellar mass-loss and exhibit stellar tidal tails, whereas Sculptor and Leo I analogues, which are more deeply embedded in their host dark matter haloes at infall, do not show substantial mass-loss due to tides. When additionally comparing the orbital motion of the host subaloes to the measured proper motion of Fornax, we find the matching more difficult; host subhaloes tend to have pericentres smaller than that measured for Fornax itself. From the kinematic and orbital data, we estimate that Fornax has lost 10-20 per cent of its infall stellar mass. Our best estimate for the surface brightness of a stellar tidal stream associated with Fornax is σ ∼32.6 mag arcsec^-2, which may be detectable with deep imaging surveys such as DES and LSST.
@article{2017MNRAS.468.4887W, author = {{Wang}, M. -Y. and {Fattahi}, Azadeh and {Cooper}, Andrew P. and {Sawala}, Till and {Strigari}, Louis E. and {Frenk}, Carlos S. and {Navarro}, Julio F. and {Oman}, Kyle and {Schaller}, Matthieu}, title = {{Tidal features of classical Milky Way satellites in a Λ cold dark matter universe}}, journal = {\mnras}, keywords = {methods: numerical, Galaxy: evolution, Galaxy: kinematics and dynamics, Local Group, dark matter, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2017}, month = jul, volume = {468}, number = {4}, pages = {4887-4901}, doi = {10.1093/mnras/stx742}, archiveprefix = {arXiv}, eprint = {1611.00778}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2017MNRAS.468.4887W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Shaken and stirred: the Milky Way’s dark substructures

Till Sawala, Pauli Pihajoki, Peter H. Johansson, and 4 more authors

(2017) MNRAS 467 4383

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The predicted abundance and properties of the low-mass substructures embedded inside larger dark matter haloes differ sharply among alternative dark matter models. Too small to host galaxies themselves, these subhaloes may still be detected via gravitational lensing or via perturbations of the Milky Way’s globular cluster streams and its stellar disc. Here, we use the Apostle cosmological simulations to predict the abundance and the spatial and velocity distributions of subhaloes in the range 10^6.5-10^8.5 M_⊙ inside haloes of mass ∼10¹² M_⊙ in Λ cold dark matter. Although these subhaloes are themselves devoid of baryons, we find that baryonic effects are important. Compared to corresponding dark matter only simulations, the loss of baryons from subhaloes and stronger tidal disruption due to the presence of baryons near the centre of the main halo reduce the number of subhaloes by ∼1/4 to 1/2, independently of subhalo mass, but increasingly towards the host halo centre. We also find that subhaloes have non-Maxwellian orbital velocity distributions, with centrally rising velocity anisotropy and positive velocity bias that reduces the number of low-velocity subhaloes, particularly near the halo centre. We parametrize the predicted population of subhaloes in terms of mass, galactocentric distance and velocities. We discuss implications of our results for the prospects of detecting dark matter substructures and for possible inferences about the nature of dark matter.
@article{2017MNRAS.467.4383S, author = {{Sawala}, Till and {Pihajoki}, Pauli and {Johansson}, Peter H. and {Frenk}, Carlos S. and {Navarro}, Julio F. and {Oman}, Kyle A. and {White}, Simon D. M.}, title = {{Shaken and stirred: the Milky Way's dark substructures}}, journal = {\mnras}, keywords = {Local Group, cosmology: theory, dark matter, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2017}, month = jun, volume = {467}, number = {4}, pages = {4383-4400}, doi = {10.1093/mnras/stx360}, archiveprefix = {arXiv}, eprint = {1609.01718}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2017MNRAS.467.4383S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Mass-Discrepancy Acceleration Relation: A Natural Outcome of Galaxy Formation in Cold Dark Matter Halos

Aaron D. Ludlow, Alejandro Benı́tez-Llambay, Matthieu Schaller, and 8 more authors

(2017) PRL 118 161103

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We analyze the total and baryonic acceleration profiles of a set of well-resolved galaxies identified in the eagle suite of hydrodynamic simulations. Our runs start from the same initial conditions but adopt different prescriptions for unresolved stellar and active galactic nuclei feedback, resulting in diverse populations of galaxies by the present day. Some of them reproduce observed galaxy scaling relations, while others do not. However, regardless of the feedback implementation, all of our galaxies follow closely a simple relationship between the total and baryonic acceleration profiles, consistent with recent observations of rotationally supported galaxies. The relation has small scatter: Different feedback implementations - which produce different galaxy populations - mainly shift galaxies along the relation rather than perpendicular to it. Furthermore, galaxies exhibit a characteristic acceleration g_†, above which baryons dominate the mass budget, as observed. These observations, consistent with simple modified Newtonian dynamics, can be accommodated within the standard cold dark matter paradigm.
@article{2017PhRvL.118p1103L, author = {{Ludlow}, Aaron D. and {Ben{\'\i}tez-Llambay}, Alejandro and {Schaller}, Matthieu and {Theuns}, Tom and {Frenk}, Carlos S. and {Bower}, Richard and {Schaye}, Joop and {Crain}, Robert A. and {Navarro}, Julio F. and {Fattahi}, Azadeh and {Oman}, Kyle A.}, title = {{Mass-Discrepancy Acceleration Relation: A Natural Outcome of Galaxy Formation in Cold Dark Matter Halos}}, journal = {\prl}, keywords = {Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2017}, month = apr, volume = {118}, number = {16}, eid = {161103}, pages = {161103}, doi = {10.1103/PhysRevLett.118.161103}, archiveprefix = {arXiv}, eprint = {1610.07663}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2017PhRvL.118p1103L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The properties of ‘dark’ ΛCDM haloes in the Local Group

Alejandro Benı́tez-Llambay, Julio F. Navarro, Carlos S. Frenk, and 7 more authors

(2017) MNRAS 465 3913

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We examine the baryon content of low-mass Λ cold dark matter (ΛCDM) haloes (10⁸ < M₂₀₀/M_⊙ < 5 × 10⁹) using the APOSTLE cosmological hydrodynamical simulations. Most of these systems are free of stars and have a gaseous content set by the combined effects of cosmic reionization, which imposes a mass-dependent upper limit, and of ram-pressure stripping, which reduces it further in high-density regions. Haloes mainly affected by reionization (RELHICS; REionization-Limited HI Clouds) inhabit preferentially low- density regions and make up a population where the gas is in hydrostatic equilibrium with the dark matter potential and in thermal equilibrium with the ionizing UV background. Their thermodynamic properties are well specified, and their gas density and temperature profiles may be predicted in detail. Gas in RELHICS is nearly fully ionized but with neutral cores that span a large range of HI masses and column densities and have negligible non-thermal broadening. We present predictions for their characteristic sizes and central column densities; the massive tail of the distribution should be within reach of future blind HI surveys. Local Group RELHICS (LGRs) have some properties consistent with observed Ultra Compact High Velocity Clouds (UCHVCs) but the sheer number of the latter suggests that most UCHVCs are not RELHICS. Our results suggest that LGRs (I) should typically be beyond 500 kpc from the Milky Way or M31; (II) have positive Galactocentric radial velocities; (III) HI sizes not exceeding 1 kpc, and (IV) should be nearly round. The detection and characterization of RELHICS would offer a unique probe of the small-scale clustering of CDM.
@article{2017MNRAS.465.3913B, author = {{Ben{\'\i}tez-Llambay}, Alejandro and {Navarro}, Julio F. and {Frenk}, Carlos S. and {Sawala}, Till and {Oman}, Kyle and {Fattahi}, Azadeh and {Schaller}, Matthieu and {Schaye}, Joop and {Crain}, Robert A. and {Theuns}, Tom}, title = {{The properties of `dark' ΛCDM haloes in the Local Group}}, journal = {\mnras}, keywords = {galaxies: haloes, Local Group, cosmology: theory, dark matter, Astrophysics - Astrophysics of Galaxies}, year = {2017}, month = mar, volume = {465}, number = {4}, pages = {3913-3926}, doi = {10.1093/mnras/stw2982}, archiveprefix = {arXiv}, eprint = {1609.01301}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2017MNRAS.465.3913B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The oldest and most metal-poor stars in the APOSTLE Local Group simulations

Else Starkenburg, Kyle A. Oman, Julio F. Navarro, and 5 more authors

(2017) MNRAS 465 2212

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We examine the spatial distribution of the oldest and most metal-poor stellar populations of Milky Way-sized galaxies using the A Project Of Simulating The Local Environment (APOSTLE) cosmological hydrodynamical simulations of the Local Group. In agreement with earlier work, we find strong radial gradients in the fraction of the oldest (t_form < 0.8 Gyr) and most metal-poor ([Fe/H] < -2.5) stars, both of which increase outwards. The most metal-poor stars form over an extended period of time; half of them form after z = 5.3, and the last 10 per cent after z = 2.8. The age of the metal-poor stellar population also shows significant variation with environment; a high fraction of them are old in the galaxy’s central regions and an even higher fraction in some individual dwarf galaxies, with substantial scatter from dwarf to dwarf. We investigate the dependence of these results on the assumptions made for metal mixing. Overall, over half of the stars that belong to both the oldest and most metal-poor population are found outside the solar circle. Somewhat counter-intuitively, we find that dwarf galaxies with a large fraction of metal-poor stars that are very old are systems where metal-poor stars are relatively rare, but where a substantial old population is present. Our results provide guidance for interpreting the results of surveys designed to hunt for the earliest and most pristine stellar component of our Milky Way.
@article{2017MNRAS.465.2212S, author = {{Starkenburg}, Else and {Oman}, Kyle A. and {Navarro}, Julio F. and {Crain}, Robert A. and {Fattahi}, Azadeh and {Frenk}, Carlos S. and {Sawala}, Till and {Schaye}, Joop}, title = {{The oldest and most metal-poor stars in the APOSTLE Local Group simulations}}, journal = {\mnras}, keywords = {stars: abundances, Galaxy: formation, galaxies: dwarf, Local Group, dark ages, reionization, first stars, early Universe, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Solar and Stellar Astrophysics}, year = {2017}, month = feb, volume = {465}, number = {2}, pages = {2212-2224}, doi = {10.1093/mnras/stw2873}, archiveprefix = {arXiv}, eprint = {1609.05214}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2017MNRAS.465.2212S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The low-mass end of the baryonic Tully-Fisher relation

Laura V. Sales, Julio F. Navarro, Kyle Oman, and 11 more authors

(2017) MNRAS 464 2419

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The scaling of disc galaxy rotation velocity with baryonic mass (the ‘baryonic Tully-Fisher’ relation, BTF) has long confounded galaxy formation models. It is steeper than the M ∝ V³ scaling relating halo virial masses and circular velocities and its zero-point implies that galaxies comprise a very small fraction of available baryons. Such low galaxy formation efficiencies may, in principle, be explained by winds driven by evolving stars, but the tightness of the BTF relation argues against the substantial scatter expected from such a vigorous feedback mechanism. We use the APOSTLE/EAGLE simulations to show that the BTF relation is well reproduced in Λcold dark matter (CDM) simulations that match the size and number of galaxies as a function of stellar mass. In such models, galaxy rotation velocities are proportional to halo virial velocity and the steep velocity-mass dependence results from the decline in galaxy formation efficiency with decreasing halo mass needed to reconcile the CDM halo mass function with the galaxy luminosity function. The scatter in the simulated BTF is smaller than observed, even when considering all simulated galaxies and not just rotationally supported ones. The simulations predict that the BTF should become increasingly steep at the faint end, although the velocity scatter at fixed mass should remain small. Observed galaxies with rotation speeds below ∼40 km s^-1 seem to deviate from this prediction. We discuss observational biases and modelling uncertainties that may help to explain this disagreement in the context of ΛCDM models of dwarf galaxy formation.
@article{2017MNRAS.464.2419S, author = {{Sales}, Laura V. and {Navarro}, Julio F. and {Oman}, Kyle and {Fattahi}, Azadeh and {Ferrero}, Ismael and {Abadi}, Mario and {Bower}, Richard and {Crain}, Robert A. and {Frenk}, Carlos S. and {Sawala}, Till and {Schaller}, Matthieu and {Schaye}, Joop and {Theuns}, Tom and {White}, Simon D. M.}, title = {{The low-mass end of the baryonic Tully-Fisher relation}}, journal = {\mnras}, keywords = {galaxies: evolution, galaxies: haloes, galaxies: structure, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2017}, month = jan, volume = {464}, number = {2}, pages = {2419-2428}, doi = {10.1093/mnras/stw2461}, archiveprefix = {arXiv}, eprint = {1602.02155}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2017MNRAS.464.2419S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2016

Satellite quenching time-scales in clusters from projected phase space measurements matched to simulated orbits

Kyle A. Oman, and Michael J. Hudson

(2016) MNRAS 463 3083

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We measure the star formation quenching efficiency and time-scale in cluster environments. Our method uses N-body simulations to estimate the probability distribution of possible orbits for a sample of observed Sloan Digital Sky Survey galaxies in and around clusters based on their position and velocity offsets from their host cluster. We study the relationship between their star formation rates and their likely orbital histories via a simple model in which star formation is quenched once a delay time after infall has elapsed. Our orbit library method is designed to isolate the environmental effect on the star formation rate due to a galaxy’s present-day host cluster from ‘pre-processing’ in previous group hosts. We find that quenching of satellite galaxies of all stellar masses in our sample (10⁹-10^11.5 M_⊙) by massive (>10¹³ M_⊙) clusters is essentially 100 per cent efficient. Our fits show that all galaxies quench on their first infall, approximately at or within a Gyr of their first pericentric passage. There is little variation in the onset of quenching from galaxy-to-galaxy: the spread in this time is at most ∼2 Gyr at fixed M_★. Higher mass satellites quench earlier, with very little dependence on host cluster mass in the range probed by our sample.
@article{2016MNRAS.463.3083O, author = {{Oman}, Kyle A. and {Hudson}, Michael J.}, title = {{Satellite quenching time-scales in clusters from projected phase space measurements matched to simulated orbits}}, journal = {\mnras}, keywords = {galaxies: clusters: general, galaxies: evolution, Astrophysics - Astrophysics of Galaxies}, year = {2016}, month = dec, volume = {463}, number = {3}, pages = {3083-3095}, doi = {10.1093/mnras/stw2195}, archiveprefix = {arXiv}, eprint = {1607.07934}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2016MNRAS.463.3083O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The low abundance and insignificance of dark discs in simulated Milky Way galaxies

Matthieu Schaller, Carlos S. Frenk, Azadeh Fattahi, and 3 more authors

(2016) MNRAS 461 L56

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We investigate the presence and importance of dark matter discs in a sample of 24 simulated Milky Way galaxies in the APOSTLE project, part of the EAGLE programme of hydrodynamic simulations in ΛCDM cosmology. It has been suggested that a dark disc in the Milky Way may boost the dark matter density and modify the velocity modulus relative to a smooth halo at the position of the Sun, with ramifications for direct detection experiments. From a kinematic decomposition of the dark matter and a real space analysis of all 24 haloes, we find that only one of the simulated Milky Way analogues has a detectable dark disc component. This unique event was caused by a merger at late time with an LMC-mass satellite at very low grazing angle. Considering that even this rare scenario only enhances the dark matter density at the solar radius by 35 per cent and affects the high-energy tail of the dark matter velocity distribution by less than 1 per cent, we conclude that the presence of a dark disc in the Milky Way is unlikely, and is very unlikely to have a significant effect on direct detection experiments.
@article{2016MNRAS.461L..56S, author = {{Schaller}, Matthieu and {Frenk}, Carlos S. and {Fattahi}, Azadeh and {Navarro}, Julio F. and {Oman}, Kyle A. and {Sawala}, Till}, title = {{The low abundance and insignificance of dark discs in simulated Milky Way galaxies}}, journal = {\mnras}, keywords = {methods: numerical, Galaxy: disc, Galaxy: structure, cosmology: theory, dark matter, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology}, year = {2016}, month = sep, volume = {461}, number = {1}, pages = {L56-L61}, doi = {10.1093/mnrasl/slw101}, archiveprefix = {arXiv}, eprint = {1605.02770}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2016MNRAS.461L..56S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Missing dark matter in dwarf galaxies?

Kyle A. Oman, Julio F. Navarro, Laura V. Sales, and 5 more authors

(2016) MNRAS 460 3610

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We use cosmological hydrodynamical simulations of the APOSTLE project along with high-quality rotation curve observations to examine the fraction of baryons in ΛCDM haloes that collect into galaxies. This ‘galaxy formation efficiency’ correlates strongly and with little scatter with halo mass, dropping steadily towards dwarf galaxies. The baryonic mass of a galaxy may thus be used to place a lower limit on total halo mass and, consequently, on its asymptotic maximum circular velocity. A number of observed dwarfs seem to violate this constraint, having baryonic masses up to 10 times higher than expected from their rotation speeds, or, alternatively, rotating at only half the speed expected for their mass. Taking the data at face value, either these systems have formed galaxies with extraordinary efficiency - highly unlikely given their shallow potential wells - or their dark matter content is much lower than expected from ΛCDM haloes. This ‘missing dark matter’ is reminiscent of the inner mass deficit of galaxies with slowly rising rotation curves, but cannot be explained away by star formation-induced ‘cores’ in the dark mass profile, since the anomalous deficit applies to regions larger than the luminous galaxies themselves. We argue that explaining the structure of these galaxies would require either substantial modification of the standard ΛCDM paradigm or else significant revision to the uncertainties in their inferred mass profiles, which should be much larger than reported. Systematic errors in inclination may provide a simple resolution to what would otherwise be a rather intractable problem for the current paradigm.
@article{2016MNRAS.460.3610O, author = {{Oman}, Kyle A. and {Navarro}, Julio F. and {Sales}, Laura V. and {Fattahi}, Azadeh and {Frenk}, Carlos S. and {Sawala}, Till and {Schaller}, Matthieu and {White}, Simon D. M.}, title = {{Missing dark matter in dwarf galaxies?}}, journal = {\mnras}, keywords = {galaxies: haloes, galaxies: structure, dark matter, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2016}, month = aug, volume = {460}, number = {4}, pages = {3610-3623}, doi = {10.1093/mnras/stw1251}, archiveprefix = {arXiv}, eprint = {1601.01026}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2016MNRAS.460.3610O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The cold dark matter content of Galactic dwarf spheroidals: no cores, no failures, no problem

Azadeh Fattahi, Julio F. Navarro, Till Sawala, and 5 more authors

(2016) arXiv 1607.06479

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We examine the dark matter content of satellite galaxies in Lambda-CDM cosmological hydrodynamical simulations of the Local Group from the APOSTLE project. We find excellent agreement between simulation results and estimates for the 9 brightest Galactic dwarf spheroidals (dSphs) derived from their stellar velocity dispersions and half-light radii. Tidal stripping plays an important role by gradually removing dark matter from the outside in, affecting in particular fainter satellites and systems of larger-than-average size for their luminosity. Our models suggest that tides have significantly reduced the dark matter content of Can Ven I, Sextans, Carina, and Fornax, a prediction that may be tested by comparing them with field galaxies of matching luminosity and size. Uncertainties in observational estimates of the dark matter content of individual dwarfs have been underestimated in the past, at times substantially. We use our improved estimates to revisit the ‘too-big-to-fail’ problem highlighted in earlier N-body work. We reinforce and extend our previous conclusion that the APOSTLE simulations show no sign of this problem. The resolution does not require ‘cores’ in the dark mass profiles, but, rather, relies on revising assumptions and uncertainties in the interpretation of observational data and accounting for ‘baryon effects’ in the theoretical modelling.
@article{2016arXiv160706479F, author = {{Fattahi}, Azadeh and {Navarro}, Julio F. and {Sawala}, Till and {Frenk}, Carlos S. and {Sales}, Laura V. and {Oman}, Kyle and {Schaller}, Matthieu and {Wang}, Jie}, title = {{The cold dark matter content of Galactic dwarf spheroidals: no cores, no failures, no problem}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2016}, month = jul, eid = {arXiv:1607.06479}, pages = {arXiv:1607.06479}, doi = {10.48550/arXiv.1607.06479}, archiveprefix = {arXiv}, eprint = {1607.06479}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2016arXiv160706479F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The APOSTLE simulations: solutions to the Local Group’s cosmic puzzles

Till Sawala, Carlos S. Frenk, Azadeh Fattahi, and 13 more authors

(2016) MNRAS 457 1931

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The Local Group galaxies offer some of the most discriminating tests of models of cosmic structure formation. For example, observations of the Milky Way (MW) and Andromeda satellite populations appear to be in disagreement with N-body simulations of the ‘lambda cold dark matter’ (ΛCDM) model: there are far fewer satellite galaxies than substructures in CDM haloes (the ‘missing satellites’ problem); dwarf galaxies seem to avoid the most massive substructures (the ‘too-big-to-fail’ problem); and the brightest satellites appear to orbit their host galaxies on a thin plane (the ‘planes of satellites’ problem). Here we present results from APOSTLE (A Project Of Simulating The Local Environment), a suite of cosmological hydrodynamic simulations of 12 volumes selected to match the kinematics of the Local Group (LG) members. Applying the EAGLE code to the LG environment, we find that our simulations match the observed abundance of LG galaxies, including the satellite galaxies of the MW and Andromeda. Due to changes to the structure of haloes and the evolution in the LG environment, the simulations reproduce the observed relation between stellar mass and velocity dispersion of individual dwarf spheroidal galaxies without necessitating the formation of cores in their dark matter profiles. Satellite systems form with a range of spatial anisotropies, including one similar to the MWs, confirming that such a configuration is not unexpected in ΛCDM. Finally, based on the observed velocity dispersion, size, and stellar mass, we provide estimates of the maximum circular velocity for the haloes of nine MW dwarf spheroidals.
@article{2016MNRAS.457.1931S, author = {{Sawala}, Till and {Frenk}, Carlos S. and {Fattahi}, Azadeh and {Navarro}, Julio F. and {Bower}, Richard G. and {Crain}, Robert A. and {Dalla Vecchia}, Claudio and {Furlong}, Michelle and {Helly}, John. C. and {Jenkins}, Adrian and {Oman}, Kyle A. and {Schaller}, Matthieu and {Schaye}, Joop and {Theuns}, Tom and {Trayford}, James and {White}, Simon D. M.}, title = {{The APOSTLE simulations: solutions to the Local Group's cosmic puzzles}}, journal = {\mnras}, keywords = {galaxies: evolution, galaxies: formation, cosmology: theory, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2016}, month = apr, volume = {457}, number = {2}, pages = {1931-1943}, doi = {10.1093/mnras/stw145}, archiveprefix = {arXiv}, eprint = {1511.01098}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2016MNRAS.457.1931S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
The APOSTLE project: Local Group kinematic mass constraints and simulation candidate selection

Azadeh Fattahi, Julio F. Navarro, Till Sawala, and 8 more authors

(2016) MNRAS 457 844

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We use a large sample of isolated dark matter halo pairs drawn from cosmological N-body simulations to identify candidate systems whose kinematics match that of the Local Group (LG) of galaxies. We find, in agreement with the ‘timing argument’ and earlier work, that the separation and approach velocity of the Milky Way (MW) and Andromeda (M31) galaxies favour a total mass for the pair of ∼5×10¹² M_⊙. A mass this large, however, is difficult to reconcile with the small relative tangential velocity of the pair, as well as with the small deceleration from the Hubble flow observed for the most distant LG members. Halo pairs that match these three criteria have average masses a factor of ∼2 times smaller than suggested by the timing argument, but with large dispersion. Guided by these results, we have selected 12 halo pairs with total mass in the range 1.6-3.6×10¹² M_⊙ for the APOSTLE project (A Project Of Simulating The Local Environment), a suite of hydrodynamical resimulations at various numerical resolution levels (reaching up to ∼10⁴ M_⊙ per gas particle) that use the subgrid physics developed for the EAGLE project. These simulations reproduce, by construction, the main kinematics of the MW-M31 pair, and produce satellite populations whose overall number, luminosities, and kinematics are in good agreement with observations of the MW and M31 companions. The APOSTLE candidate systems thus provide an excellent testbed to confront directly many of the predictions of the Λ cold dark matter cosmology with observations of our local Universe.
@article{2016MNRAS.457..844F, author = {{Fattahi}, Azadeh and {Navarro}, Julio F. and {Sawala}, Till and {Frenk}, Carlos S. and {Oman}, Kyle A. and {Crain}, Robert A. and {Furlong}, Michelle and {Schaller}, Matthieu and {Schaye}, Joop and {Theuns}, Tom and {Jenkins}, Adrian}, title = {{The APOSTLE project: Local Group kinematic mass constraints and simulation candidate selection}}, journal = {\mnras}, keywords = {methods: numerical, galaxies: dwarf, galaxies: haloes, Local Group, dark matter, Astrophysics - Astrophysics of Galaxies}, year = {2016}, month = mar, volume = {457}, number = {1}, pages = {844-856}, doi = {10.1093/mnras/stv2970}, archiveprefix = {arXiv}, eprint = {1507.03643}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2016MNRAS.457..844F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2015

The unexpected diversity of dwarf galaxy rotation curves

Kyle A. Oman, Julio F. Navarro, Azadeh Fattahi, and 9 more authors

(2015) MNRAS 452 3650

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We examine the circular velocity profiles of galaxies in Λ cold dark matter (CDM) cosmological hydrodynamical simulations from the EAGLE and LOCAL GROUPS projects and compare them with a compilation of observed rotation curves of galaxies spanning a wide range in mass. The shape of the circular velocity profiles of simulated galaxies varies systematically as a function of galaxy mass, but shows remarkably little variation at fixed maximum circular velocity. This is especially true for low-mass dark-matter-dominated systems, reflecting the expected similarity of the underlying CDM haloes. This is at odds with observed dwarf galaxies, which show a large diversity of rotation curve shapes, even at fixed maximum rotation speed. Some dwarfs have rotation curves that agree well with simulations, others do not. The latter are systems where the inferred mass enclosed in the inner regions is much lower than expected for CDM haloes and include many galaxies where previous work claims the presence of a constant density ‘core’. The ‘cusp versus core’ issue is thus better characterized as an ‘inner mass deficit’ problem than as a density slope mismatch. For several galaxies, the magnitude of this inner mass deficit is well in excess of that reported in recent simulations where cores result from baryon-induced fluctuations in the gravitational potential. We conclude that one or more of the following statements must be true: (i) the dark matter is more complex than envisaged by any current model; (ii) current simulations fail to reproduce the diversity in the effects of baryons on the inner regions of dwarf galaxies; and/or (iii) the mass profiles of ‘inner mass deficit’ galaxies inferred from kinematic data are incorrect.
@article{2015MNRAS.452.3650O, author = {{Oman}, Kyle A. and {Navarro}, Julio F. and {Fattahi}, Azadeh and {Frenk}, Carlos S. and {Sawala}, Till and {White}, Simon D. M. and {Bower}, Richard and {Crain}, Robert A. and {Furlong}, Michelle and {Schaller}, Matthieu and {Schaye}, Joop and {Theuns}, Tom}, title = {{The unexpected diversity of dwarf galaxy rotation curves}}, journal = {\mnras}, keywords = {galaxies: haloes, galaxies: structure, dark matter, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2015}, month = oct, volume = {452}, number = {4}, pages = {3650-3665}, doi = {10.1093/mnras/stv1504}, archiveprefix = {arXiv}, eprint = {1504.01437}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2015MNRAS.452.3650O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2014

Quenching star formation in cluster galaxies

Dan S. Taranu, Michael J. Hudson, Michael L. Balogh, and 4 more authors

(2014) MNRAS 440 1934

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In order to understand the processes that quench star formation in cluster galaxies, we construct a library of subhalo orbits drawn from Λ cold dark matter cosmological N-body simulations of four rich clusters. We combine these orbits with models of star formation followed by environmental quenching, comparing model predictions with observed bulge and disc colours and stellar absorption line-strength indices of luminous cluster galaxies. Models in which the bulge stellar populations depend only on the galaxy subhalo mass while the disc is quenched upon infall are acceptable fits to the data. An exponential disc quenching time-scale of 3-3.5 Gyr is preferred. Quenching in lower mass groups prior to infall (‘pre-processing’) provides better fits, with similar quenching time-scales. Models with short (≲1 Gyr) quenching time-scales yield excessively steep cluster-centric gradients in disc colours and Balmer line indices, even if quenching is delayed for several Gyr. The data slightly prefer models where quenching occurs only for galaxies falling within ∼0.5r₂₀₀. These results imply that the environments of rich clusters must impact star formation rates of infalling galaxies on relatively long time-scales, indicative of gentler quenching mechanisms such as slow ‘strangulation’ over more rapid ram-pressure stripping.
@article{2014MNRAS.440.1934T, author = {{Taranu}, Dan S. and {Hudson}, Michael J. and {Balogh}, Michael L. and {Smith}, Russell J. and {Power}, Chris and {Oman}, Kyle A. and {Krane}, Brad}, title = {{Quenching star formation in cluster galaxies}}, journal = {\mnras}, keywords = {galaxies: clusters: general, galaxies: evolution, galaxies: formation, galaxies: haloes, galaxies: star formation, galaxies: stellar content, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2014}, month = may, volume = {440}, number = {3}, pages = {1934-1949}, doi = {10.1093/mnras/stu389}, archiveprefix = {arXiv}, eprint = {1211.3411}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2014MNRAS.440.1934T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }

2013

Probing the Environmental Dependence of Star Formation in Satellite Galaxies using Orbital Kinematics

Kyle Oman

(2013) MSc Thesis, University of Waterloo

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(Abridged) Physical processes regulating star formation in satellite galaxies represent an area of ongoing research, but the projected nature of observed coordinates makes separating different populations of satellites (with different processes at work) difficult. The present-day phase space coordinates of a satellite galaxy carry information about its orbital history, which can then be compared to its star formation history (SFH). This is expected to reveal both a trigger time and timescale for environmental quenching. Finally, this can be related back to the physical process(es) regulating star formation in high density environments. We use merger trees from the MultiDark Run 1 N-body simulation to compile a catalogue of satellite orbits in cluster environments. We parameterize the orbital history by the time since crossing within 2.5 virial radii of the cluster centre and use our catalogue to estimate the probability density over a range of this parameter given a set of projected phase space coordinates. We show that different populations of satellite haloes occupy (semi-)distinct regions of (projected) phase space. We generalize this result by producing a probability distribution function (PDF) of possible infall times at every point in projected phase space. We apply our method to determining the infall time PDFs of a large sample of observed cluster satellite candidates from the Sloan Digital Sky Survey. We use galaxy colour as a proxy for SFH and model the distribution of satellite galaxy colours as two gaussian populations. We derive a Markov chain Monte-Carlo method to obtain the colour distribution as a function of the time since infall into the cluster environment. Our implementation of this method is still being tuned, but we use a second simpler (but much cruder) method to obtain an estimate of the evolution of the colour distribution. Our results are suggestive of a quenching process that begins within perhaps ±1 Gyr of virial radius crossing and which slows after pericentric passage. We stress that results obtained with this second method come with important caveats.
@mastersthesis{2013MScT.........9O, author = {{Oman}, Kyle}, title = {{Probing the Environmental Dependence of Star Formation in Satellite Galaxies using Orbital Kinematics}}, school = {University of Waterloo, Department of Physics and Astronomy}, year = {2013}, month = sep, doi = {10012/7840}, adsurl = {https://ui.adsabs.harvard.edu/abs/2013MScT.........9O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }
Disentangling satellite galaxy populations using orbit tracking in simulations

Kyle A. Oman, Michael J. Hudson, and Peter S. Behroozi

(2013) MNRAS 431 2307

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Physical processes regulating star formation in satellite galaxies represent an area of ongoing research, but the projected nature of observed coordinates makes separating different populations of satellites (with different processes at work) difficult. The orbital history of a satellite galaxy leads to its present-day phase space coordinates; we can also work backwards and use these coordinates to statistically infer information about the orbital history. We use merger trees from the MultiDark Run 1 N-body simulation to compile a catalogue of the orbits of satellite haloes in cluster environments. We parametrize the orbital history by the time since crossing within 2.5 r_vir of the cluster centre and use our catalogue to estimate the probability density over a range of this parameter given a set of present-day projected (i.e. observable) phase space coordinates. We show that different populations of satellite haloes, e.g. infalling, backsplash and virialized, occupy distinct regions of phase space and semidistinct regions of projected phase space. This will allow us to probabilistically determine the time since infall of a large sample of observed satellite galaxies, and ultimately to study the effect of orbital history on star formation history (the topic of a future paper). We test the accuracy of our method and find that we can reliably recover this time within ±2.58 Gyr in 68 per cent of cases by using all available phase space coordinate information, compared to ±2.64 Gyr using only position coordinates and ±3.10 Gyr guessing ‘blindly’, i.e. using no coordinate information, but with knowledge of the overall distribution of infall times. In some regions of phase space, the accuracy of the infall time estimate improves to ±1.85 Gyr. Although we focus on time since infall, our method is easily generalizable to other orbital parameters (e.g. pericentric distance and time).
@article{2013MNRAS.431.2307O, author = {{Oman}, Kyle A. and {Hudson}, Michael J. and {Behroozi}, Peter S.}, title = {{Disentangling satellite galaxy populations using orbit tracking in simulations}}, journal = {\mnras}, keywords = {galaxies: clusters: general, galaxies: haloes, galaxies: kinematics and dynamics, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2013}, month = may, volume = {431}, number = {3}, pages = {2307-2316}, doi = {10.1093/mnras/stt328}, archiveprefix = {arXiv}, eprint = {1301.6757}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2013MNRAS.431.2307O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, }