We analyze the kinematics as a function of stellar age for Andromeda (M31) mass analogs from the IllustrisTNG cosmological simulation. We divide the star particles into four age groups: less than 1 Gyr, 1 to 5 Gyr, 5 to 10 Gyr, and greater 10 Gyr, and compare the kinematics of these groups to that of the neutral gas cells. We calculate rotation curves for the stellar and gaseous components of each analog from 2 kpc to 20 kpc from the center of mass. We find that the lag, or asymmetric drift (AD), between the gas rotation curve and the stellar rotation curve on average increases with stellar age. This finding is consistent with observational measurements of AD in the disk of the Andromeda galaxy. When the M31 analogs are separated into groups based on merger history, we find that there is a difference in the AD of the analogs that have had a 4:1 merger the last 4 Gyr, 8 Gyr, or 12 Gyr compared to analogs that have not experienced a 4:1 merger in the same time frame. The subset of analogs that have had a 4:1 merger within the last 4 Gyr are also similar to AD measurements of stars in the disk of M31, providing evidence that M31 may in fact have recently merged with a galaxy nearly one fourth of its mass. Further work using high resolution zoom in simulations is required to explore the contribution of internal heating to AD.
Our Milky Way provides a unique test case for galaxy evolution models, thanks to our privileged position within the Milky Way's disc. This position also complicates comparisons between the Milky Way and external galaxies, due to our inability to observe the Milky Way from an external point of view. Milky Way analog galaxies offer us a chance to bridge this divide by providing the external perspective that we otherwise lack. However, over-precise definitions of "analog" yield little-to-no galaxies, so it is vital to understand which selection criteria produce the most meaningful analog samples.…
We present the properties of Milky Way- and Andromeda-like (MW/M31-like) galaxies simulated within TNG50, the highest-resolution run of the IllustrisTNG suite of $Λ$CDM magneto-hydrodynamical simulations. We introduce our fiducial selection for MW/M31 analogs, which we propose for direct usage as well as for reference in future analyses. TNG50 contains 198 MW/M31 analogs, i.e. galaxies with stellar disky morphology, with a stellar mass in the range of $M_* = 10^{10.5 - 11.2}$ Msun, and within a MW-like Mpc-scale environment at z=0. These are resolved with baryonic (dark matter) mass resolution…
The galaxy Malin 1 contains the largest stellar disk known but the formation mechanism of this structure has been elusive. In this paper, we report a Malin 1 analogue in the 100 Mpc IllustrisTNG simulation and describe its formation history. At redshift zero, this massive galaxy, having a maximum circular velocity $V_{\rm max}$ of 430 ${\rm km\ s^{-1}}$, contains a 100 kpc gas/stellar disk with morphology similar to Malin 1. The simulated galaxy reproduces well many observed features of Malin 1's vast disk, including its stellar ages, metallicities, and gas rotation curve. We trace the extende…
With a central surface brightness of $μ_0=29.3$ mag. per sq. arcsec, and half-light radius of $r_{\rm half}=3.1^{+0.9}_{-1.1}$~kpc, Andromeda XIX (And XIX) is an extremely diffuse satellite of Andromeda. We present spectra for $\sim100$ red giant branch stars in this galaxy, plus 16 stars in a nearby stellar stream. With this exquisite dataset, we re-derive the properties of And XIX, measuring a systemic velocity of $v_r=-109.0\pm1.6$ km/s and a velocity dispersion of $σ_v = 7.8^{+1.7}_{-1.5}$ km/s (higher than derived in our previous work). We marginally detect a velocity gradient along the m…
We model dust evolution in Milky Way-like galaxies by post-processing the IllustrisTNG cosmological hydrodynamical simulations in order to predict dust-to-gas ratios and grain size distributions. We treat grain-size-dependent dust growth and destruction processes using a 64-bin discrete grain size evolution model without spatially resolving each galaxy. Our model broadly reproduces the observed dust--metallicity scaling relation in nearby galaxies. The grain size distribution is dominated by large grains at $z\gtrsim 3$ and the small-grain abundance rapidly increases by shattering and accretio…
To understand how the evolution of grain size distribution in galaxies affects observed dust properties, we apply a post-processing dust evolution model to galaxy merger trees from the IllustrisTNG cosmological hydrodynamical simulation. Our dust model includes stellar dust production, sputtering in hot gas, dust growth by accretion and coagulation in the dense interstellar medium (ISM), and shattering in the diffuse ISM. We decompose the grain size distribution into different dust species depending on the elemental abundances and the dense ISM fraction given by the simulation. In our previous…
Space observatories like the Hubble Space Telescope and Gaia are providing unprecedented 6D phase space information of satellite galaxies. Such measurements can shed light on the structure and assembly history of the Local Group, but improved statistical methods are needed to use them efficiently. Here we illustrate such a method using analogs of the Local Group's two most massive satellite galaxies, the Large Magellanic Cloud (LMC) and Triangulum (M33), from the Illustris dark-matter-only cosmological simulation. We use a Bayesian inference scheme combining measurements of positions, velociti…
We present the first comparison between the lifetime star formation histories (SFHs) of M31 and Milky Way (MW) satellites. Using the Advanced Camera for Surveys aboard the Hubble Space Telescope, we obtained deep optical imaging of Andromeda II (M$_{V} = -$12.0; log(M$_{\star}$/M$_{\odot}$) $\sim$ 6.7) and Andromeda XVI (M$_{V} = -$7.5; log(M$_{\star}$/M$_{\odot}$) $\sim$ 4.9) yielding color-magnitude diagrams that extend at least 1 magnitude below the oldest main sequence turnoff, and are similar in quality to those available for the MW companions. And II and And XVI show strikingly similar S…
Half of the satellite galaxies of Andromeda form a narrow plane termed the Great Plane of Andromeda (GPoA), and their line-of-sight velocities display correlation reminiscent of a rotating structure. Recently reported first proper motion measurements for the on-plane satellites NGC 147 and NGC 185 indicate that they indeed co-orbit along the GPoA. This provides a novel opportunity to compare the M31 satellite system to $Λ$CDM expectations. We perform the first detailed comparison of the orbital alignment of two satellite galaxies beyond the Milky Way with several hydrodynamical and dark-matter…
We explore the radial distribution of satellite galaxies in groups in the Galaxy and Mass Assembly (GAMA) survey and the IllustrisTNG simulations. Considering groups with masses $12.0 \leq \log_{10} (\mathcal{M}_h / h^{-1} \mathrm{M}_{\odot}) < 14.8$ at $z<0.267$, we find a good agreement between GAMA and a sample of TNG300 groups and galaxies designed to match the GAMA selection. Both display a flat profile in the centre of groups, followed by a decline that becomes steeper towards the group edge, and normalised profiles show no dependence on group mass. Using matched satellites from TNG and …
The Merger-Driven Origin of the Vast Extended Stellar Disc Around the Andromeda Galaxy
National and Kapodistrian University of Athens（雅典国立卡波蒂斯坦大学）；European Southern Observatory（欧洲南方天文台）；Observatoire de Paris（巴黎天文台）；PSL Research University（PSL研究大学）；CNRS（法国国家科学研究中心）；Max-Planck-Institut für extraterrestrische Physik (MPE)（马克斯·普朗克地外物理研究所）；University Observatory Munich (USM)（慕尼黑大学天文台）
In this work an ensemble of simulated Local Group analogues is used to constrain the properties of the mass assembly history of the Milky Way (MW) and Andromeda (M31) galaxies. These objects have been obtained using the constrained simulation technique, which ensures that simulated LGs live within a large scale environment akin to the observed one. Our results are compared against a standard $Λ$ Cold Dark Matter ($Λ$CDM) series of simulations which use the same cosmological parameters. This allows us to single out the effects of the constraints on the results. We find that (a) the median const…
Learning the Universe with the 2nd Generation of CAMELS: Varying 35 parameters of the IllustrisTNG model in (50Mpc/h)^3 boxes
Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理学中心）；Columbia Astrophysics Laboratory, Columbia University（哥伦比亚大学天体物理实验室，哥伦比亚大学）；NSF-Simons AI Institute for the Sky (SkAI)（NSF-西蒙斯天空人工智能研究所（SkAI））；School of Physics, Korea Institute for Advanced Study（韩国高等科学研究院物理学院）；Department of Physics, University of Connecticut（康涅狄格大学物理系）；Department of Physics and Astronomy, Rutgers University（罗格斯大学物理与天文系）；Department of Astronomy, Columbia University（哥伦比亚大学天文系）；Department of Astrophysical Sciences, Princeton University（普林斯顿大学天体物理科学系）；TransferLab, appliedAI Institute for Europe（欧洲应用人工智能研究所 TransferLab）；Kavli Institute for Cosmology, Madingley Road, Cambridge CB3 0HA, UK（剑桥大学卡弗里宇宙学研究所）；Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK（剑桥大学天文学研究所）
The satellites of the Milky Way and Andromeda represent the smallest galaxies we can observe in our Universe. In this series of papers we aim to shed light on their formation and evolution using cosmological hydrodynamical simulations. In this first paper we focus on the galaxy properties before accretion, by simulating twenty seven haloes with masses between $5\times 10^8$ and $10^{10} M_\odot$. Out of this set nineteen haloes successfully form stars, while eight remain dark. The simulated galaxies match quite well present day observed scaling relations between stellar mass, size and metallic…
We analyze the merger and assembly histories of Milky Way (MW) and Andromeda (M31)-like galaxies to quantify how, and how often, disk galaxies of this mass can survive recent major mergers (stellar mass ratio $\ge$ 1:4). For this, we use the cosmological magneto-hydrodynamical simulation TNG50 and identify 198 analog galaxies, selected based on their $z=0$ stellar mass ($10^{10.5-11.2} {\rm M_{\odot}}$), disky stellar morphology and local environment. Firstly, major mergers are common: 85 per cent (168) of MW/M31-like galaxies in TNG50 have undergone at least one major merger across their life…
Triangulum, M33, is a low mass, relatively undisturbed spiral galaxy that offers a new regime in which to test models of dynamical heating. In spite of its proximity, the dynamical heating history of M33 has not yet been well constrained. In this work, we present the TREX Survey, the largest stellar spectroscopic survey across the disk of M33. We present the stellar disk kinematics as a function of age to study the past and ongoing dynamical heating of M33. We measure line of sight velocities for ~4,500 disk stars. Using a subset, we divide the stars into broad age bins using Hubble Space Tele…
We use the TNG50 simulation of the IllustrisTNG project to study cold, dense clouds of gas in the circumgalactic media (CGM) of Milky Way-like galaxies. We find that their CGM is typically filled with of order one hundred (thousand) reasonably (marginally) resolved clouds, possible analogs of high-velocity clouds (HVCs). There is a large variation in cloud abundance from galaxy to galaxy, and the physical properties of clouds that we explore -- mass, size, metallicity, pressure, and kinematics -- are also diverse. We quantify the distributions of cloud properties and cloud-background contrasts…
Recent observations have revealed remarkable insights into the gas reservoir in the circumgalactic medium (CGM) of galaxy haloes. In this paper, we characterise the gas in the vicinity of Milky Way and Andromeda analogues in the HESTIA (High resolution Environmental Simulations of The Immediate Area) suite of constrained Local Group (LG) simulations. The HESTIA suite comprise of a set of three high-resolution {\sc arepo}-based simulations of the LG, run using the Auriga galaxy formation model. For this paper, we focus only on the $z = 0$ simulation datasets and generate mock skymaps along with…
We quantify the impact of galaxy formation on dark matter halo shapes using cosmological simulations at redshift $z=0$. The haloes are drawn from the IllustrisTNG project, a suite of magneto-hydrodynamic simulations of galaxies. We focus on haloes of mass $10^{10-14} M_\odot$ from the 50-Mpc (TNG50) and 100-Mpc (TNG100) boxes, and compare them to dark matter-only (DMO) analogues and other simulations e.g. NIHAO and Eagle. We further quantify the prediction uncertainty by varying the baryonic feedback models in a series of smaller 25 Mpc $h^{-1}$ boxes. We find that: (i) galaxy formation result…
Satellite galaxies of the Milky Way and of the Andromeda galaxy have been found to preferentially align in significantly flattened planes of satellite galaxies, and available velocity measurements are indicative of a preference of satellites in those structures to co-orbit. There is increasing evidence that such kinematically correlated satellite planes are also present around more distant hosts. Detailed comparisons show that similarly anisotropic phase-space distributions of sub-halos are exceedingly rare in cosmological simulations based on the $Λ$CDM paradigm. Analogs to the observed syste…
We identify Local Group (LG) analogs in the IllustrisTNG cosmological simulation, and use these to study two mass estimators for the LG: one based on the timing argument (TA) and one based on the virial theorem (VT). Including updated measurements of the Milky Way-M31 tangential velocity and the cosmological constant, we show that the TA mass estimator slightly overestimates the true median LG-mass, though the ratio of the TA to the true mass is consistent at the approximate 90\% c.l. These are in broad agreement with previous results using dark matter-only simulations. We show that the VT est…
We study the abundance of satellite galaxies around 198 Milky Way- (MW) and M31-like hosts in TNG50, the final instalment in the IllustrisTNG suite of cosmological magnetohydrodynamical simulations. MW/M31-like analogues are defined as disky galaxies with stellar masses of Mstar = 10^10.5-11.2 Msun in relative isolation at z = 0. By defining satellites as galaxies with Mstar > 5*10^6 Msun within 300 kpc (3D) of their host, we find a remarkable level of diversity and host-to-host scatter across individual host galaxies. The median (16th - 84th percentiles) TNG50 MW/M31-like galaxy hosts a total…
We model satellite quenching at $z \sim 1$ by combining $14$ massive ($10^{13.8} < M_{\mathrm{halo}}/\mathrm{M}_{\odot} < 10^{15}$) clusters at $0.8 < z < 1.3$ from the GOGREEN and GCLASS surveys with accretion histories of $56$ redshift-matched analogs from the IllustrisTNG simulation. Our fiducial model, which is parameterized by the satellite quenching timescale ($τ_{\rm quench}$), accounts for quenching in our simulated satellite population both at the time of infall by using the observed coeval field quenched fraction and after infall by tuning $τ_{\rm quench}$ to reproduce the observed s…
The quenched fraction of satellites around simulated Milky Way-mass galaxies
Pomona College（波莫纳学院）；University of California, San Diego（加州大学圣迭戈分校）；California State University, San Bernardino（加州州立大学圣贝纳迪诺分校）；Carnegie Observatories（卡内基观测站）；California Polytechnic State University Pomona（加州州立理工大学波莫纳分校）；Yale University（耶鲁大学）；University of California, Davis（加州大学戴维斯分校）；University of Zurich（苏黎世大学）；University of Cambridge（剑桥大学）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）
The detection of Intermediate-Mass Black Holes (IMBHs) in dwarf galaxies is crucial to closing the gap in the wide mass distribution of black holes ($\sim 3 \, \rm M_{\odot}$ to $\sim 5 \times 10^{10} \, \rm M_{\odot}$). IMBHs originally located at the center of dwarfs that later collide with the Milky Way (MW) could be wandering, undetected, in our Galaxy. We used TNG50, the highest-resolution run of the IllustrisTNG project, to study the kinematics and dynamics of star clusters, in the appropriate mass range, acting as IMBH proxies in a MW analog galaxy. We showed that $\sim 87\%$ of our stu…
Alignment of the Milky Way and M31 with their cosmic environment. New insights from constrained Local Group simulations
Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台 LIRA，PSL 大学，索邦大学，巴黎西岱大学，CY 塞尔吉巴黎大学，法国国家科学研究中心）；Institute for Astronomy, University of Edinburgh, Royal Observatory（爱丁堡大学天文学研究所，皇家天文台）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；The Oskar Klein Centre, Department of Physics, Stockholm University（斯德哥尔摩大学奥斯卡·克莱因中心物理系）；CNRS & Sorbonne Université, UMR 7095, Institut d’Astrophysique de Paris（法国国家科学研究中心与索邦大学，UMR 7095，巴黎天体物理学研究所）
