Halo Mass Relation Research Articles

Environment Matters: Predicted Differences in the Stellar Mass–Halo Mass Relation and History of Star Formation for Dwarf Galaxies

We are entering an era in which we will be able to detect and characterize hundreds of dwarf galaxies within the Local Volume. It is already known that a strong dichotomy exists in the gas content and star formation properties of field dwarf galaxies versus satellite dwarfs of larger galaxies. In this work, we study the more subtle differences that may be detectable in galaxies as a function of distance from a massive galaxy, such as the Milky Way. We compare smoothed particle hydrodynamic simulations of dwarf galaxies formed in a Local Volume-like environment (several megaparsecs away from a massive galaxy) to those formed nearer to Milky Way–mass halos. We find that the impact of environment on dwarf galaxies extends even beyond the immediate region surrounding Milky Way–mass halos. Even before being accreted as satellites, dwarf galaxies near a Milky Way–mass halo tend to have higher stellar masses for their halo mass than more isolated galaxies. Dwarf galaxies in high-density environments also tend to grow faster and form their stars earlier. We show observational predictions that demonstrate how these trends manifest in lower quenching rates, higher H i fractions, and bluer colors for more isolated dwarf galaxies.

LATIS: Constraints on the Galaxy–Halo Connection at z ∼ 2.5 from Galaxy–Galaxy and Galaxy–Lyα Clustering

The connection between galaxies and dark matter halos is often quantified using the stellar mass–halo mass (SMHM) relation. Optical and near-infrared imaging surveys have led to a broadly consistent picture of the evolving SMHM relation based on measurements of galaxy abundances and angular correlation functions. Spectroscopic surveys at z ≳ 2 can also constrain the SMHM relation via the galaxy autocorrelation function and through the cross-correlation between galaxies and Lyα absorption measured in transverse sight lines; however, such studies are very few and have produced some unexpected or inconclusive results. We use ∼3000 spectra of z ∼ 2.5 galaxies from the Lyα Tomography IMACS Survey (LATIS) to measure the galaxy–galaxy and galaxy–Lyα correlation functions in four bins of stellar mass spanning 109.2 ≲ M */M ⊙ ≲ 1010.5. Parallel analyses of the MultiDark N-body and ASTRID hydrodynamic cosmological simulations allow us to model the correlation functions, estimate covariance matrices, and infer halo masses. We find that results of the two methods are mutually consistent and broadly accord with standard SMHM relations. This consistency demonstrates that we are able to measure and model Lyα transmission fluctuations δ F in LATIS accurately. We also show that the galaxy–Lyα cross-correlation, a free by-product of optical spectroscopic galaxy surveys at these redshifts, can constrain halo masses with similar precision to galaxy–galaxy clustering.

Do ultra diffuse galaxies with rich globular clusters systems have overly massive haloes?

ABSTRACT Some Ultra Diffuse Galaxies (UDGs) appear to host exceptionally rich globular cluster (GC) systems compared to normal galaxies of the same stellar mass. After re-examining these claims, we focus on a small sample of UDGs from the literature that have both rich GC systems (NGC >20) and a measured galaxy velocity dispersion. We find that UDGs with more GCs have higher dynamical masses and that GC-rich UDGs are dark matter dominated within their half-light radii. We extrapolate these dynamical masses to derive total halo masses assuming cuspy and cored mass profiles. We find reasonable agreement between halo masses derived from GC numbers (assuming the GC number–halo mass relation) and from cored halo profiles. This suggests that GC-rich UDGs do not follow the standard stellar mass–halo mass relation, occupying overly massive cored haloes for their stellar mass. A similar process to that invoked for some Local Group dwarfs, of early quenching, may result in GC-rich UDGs that have failed to form the expected mass of stars in a given halo (and thus giving the appearance of overly an massive halo). Simulations that correctly reproduce the known properties of GC systems associated with UDGs are needed.

The DESI One-Percent Survey: exploring a generalized SHAM for multiple tracers with the UNIT simulation

ABSTRACT We perform SubHalo Abundance Matching (SHAM) studies on UNIT simulations with {σ, Vceil, vsmear}-SHAM and {σ, Vceil, fsat}-SHAM. They are designed to reproduce the clustering on 5–30 $\, {\, h^{-1}\, {\rm Mpc}}$ of luminous red galaxies (LRGs), emission-line galaxies (ELGs), and quasi-stellar objects (QSOs) at 0.4 < z < 3.5 from DESI (Dark Energy Spectroscopic Instrument) One Percent Survey. Vceil is the incompleteness of the massive host (sub)haloes and is the key to the generalized SHAM. vsmear models the clustering effect of redshift uncertainties, providing measurements consistent with those from repeat observations. A free satellite fraction fsat is necessary to reproduce the clustering of ELGs. We find ELGs present a more complex galaxy–halo mass relation than LRGs reflected in their weak constraints on σ. LRGs, QSOs, and ELGs show increasing Vceil values, corresponding to the massive galaxy incompleteness of LRGs, the quenched star formation of ELGs and the quenched black hole accretion of QSOs. For LRGs, a Gaussian vsmear presents a better profile for subsamples at redshift bins than a Lorentzian profile used for other tracers. The impact of the statistical redshift uncertainty on ELG clustering is negligible. The best-fitting satellite fraction for DESI ELGs is around 4 per cent, lower than previous estimations for ELGs. The mean halo mass log10(〈Mvir〉) in ${{\, h^{-1}\, \mbox{M}_\odot }}{}$ for LRGs, ELGs, and QSOs are 13.16 ± 0.01, 11.90 ± 0.06, and 12.66 ± 0.45, respectively. Our generalized SHAM algorithms facilitate the production of multitracer galaxy mocks for cosmological tests.

Galaxy–dark matter connection of photometric galaxies from the HSC-SSP Survey: galaxy–galaxy lensing and the halo model

ABSTRACT We infer the connection between stellar mass of galaxies from Subaru Hyper Suprime-Cam (HSC) survey, and their dark matter halo masses in two bins of redshifts between [0.3, 0.8]. We use measurements of the weak lensing of background galaxies from Year-1 shape catalogue from the HSC survey. We bin lens galaxies in stellar mass with varying thresholds ranging from $8.6\le \log [M_*/(h^{-2}{M_\odot })]\le \, 11.2$ and use stringent cuts in the selection of source galaxies to measure the lensing signal. We model these measurements of the lensing signals together with the abundance of galaxies in the halo occupation distribution framework. We obtain constraints on the halo occupation parameters of central galaxies Mmin and σlog M along with parameters that describe the occupation of the satellite galaxies. The measurements of abundance and lensing individually constrain different degeneracy directions in Mmin− σlog M plane, thus breaking the degeneracy in these parameters. We demonstrate that the lensing measurements are best able to constrain average central halo masses, 〈Mcen〉. We compare our measurements to those obtained using the abundance and clustering of these galaxies. We find that the galaxy–dark matter connection does not vary significantly between redshift bins we explore in this study. Uncertainties in the photometric redshift of the lens galaxies need to be studied to understand the true underlying stellar mass–halo mass relation and evolution of galaxies.

Confirmation of an Anomalously Low Dark Matter Content for the Galaxy NGC 1052-DF4 from Deep, High-resolution Continuum Spectroscopy

NGC 1052-DF4 was found to be the second “galaxy lacking dark matter” in the NGC 1052 group, based on its velocity dispersion of km s−1 as measured from the radial velocities of seven of its globular clusters. Here we verify this result by measuring the stellar velocity dispersion of the galaxy. We observed the diffuse stellar light in NGC 1052-DF4 with the Keck Cosmic Web Imager in its highest-resolution mode, with km s−1. With a total science + sky exposure time of 34 hr, the resulting spectrum is exceptional in both its spectral resolution and its signal-to-noise ratio of 23 Å−1. We find a stellar velocity dispersion of km s−1, consistent with the previous measurement from the globular clusters. Combining both measurements gives a fiducial dispersion of km s−1. The implied dynamical mass within the half-light radius is . The expected velocity dispersion of NGC 1052-DF4 from the stellar mass alone is 7 ± 1 km s−1, and for a Navarro–Frenk–White (NFW) halo that follows the stellar mass–halo mass relation and the halo mass–concentration relation, the expectation is ∼30 km s−1. The low velocity dispersion rules out a normal NFW dark matter halo, and we confirm that NGC 1052-DF4 is one of at least two galaxies in the NGC 1052 group that have an anomalously low dark matter content. While any viable model for their formation should explain the properties of both galaxies, we note that NGC 1052-DF4 now poses the largest challenge, as it has the most stringent constraints on its dynamical mass.

The RESOLVE and ECO Gas in Galaxy Groups Initiative: The Group Finder and the Group H i–Halo Mass Relation

We present a four-step group-finding algorithm for the Gas in Galaxy Groups (G3) initiative, a spin-off of the z ∼ 0 REsolved Spectroscopy Of a Local VolumE (RESOLVE) and Environmental COntext (ECO) surveys. In preparation for future comparisons to intermediate redshift (e.g., the LADUMA survey), we design the group finder to adapt to incomplete, shallow, or nonuniform data. We use mock catalogs to optimize the group finder’s performance. Compared to friends-of-friends (with false-pair splitting), the G3 algorithm offers improved completeness and halo-mass recovery with minimal loss of purity. Combining it with the volume-limited H i census data for RESOLVE and ECO, we examine the H i content of galaxy groups as a function of group halo mass. Group-integrated H i mass M H I,grp rises monotonically over halo masses M halo ∼ 1011–1014.5 M ⊙, pivoting in slope at M halo ∼ 1011.4 M ⊙, the gas-richness threshold scale. We present the first measurement of the scatter in this relation, which has a median of ∼0.3 dex and is asymmetric toward lower M H I,grp. We discuss interesting tensions with theoretical predictions and prior measurements of the M H I,grp–M halo relation. In an appendix, we release RESOLVE DR4 and ECO DR3, including updates to survey redshifts, photometry, and group catalogs, as well as a major expansion of the ECO H i inventory with value-added data products.

Stellar mass dependence of galaxy size–dark matter halo radius relation probed by Subaru-HSC survey weak lensing measurements

ABSTRACT We investigate the stellar mass dependence of the galaxy size–dark matter halo radius relation for low-redshift galaxies using weak gravitational lensing measurements. Our sample consists of ∼38 000 galaxies more massive than $10^{8}\, {\rm M}_{\odot }\, h^{-2}$ and within z < 0.3 drawn from the overlap of Galaxy And Mass Assembly survey data release 4 and HSC-SSP PDR2. We divide our sample into a number of stellar mass bins and measure stacked weak lensing signals. We model the signals using a conditional stellar mass function to infer the stellar mass–halo mass relation. We fit a single Sérsic model to HSC i-band images of our galaxies and obtain their three-dimensional half-light radii. We use these measurements to construct a median galaxy size–mass relation. We then combine these relations to infer the galaxy size–halo radius relation. We confirm that this relation appears linear, given the statistical errors, i.e. the ratio of galaxy size to halo radius remains constant over two orders of magnitudes in stellar mass above $\sim 10^{9} \, {\rm M}_{\odot }\, h^{-2}$. Extrapolating the stellar mass–halo mass relation below this limit, we see an indication of a decreasing galaxy size–halo radius ratio with the decline in stellar mass. At stellar mass $\sim 10^{8} \, {\rm M}_{\odot }\, h^{-2}$, the ratio becomes 30 per cent smaller than its value in linear regime. The possible existence of a such trend in dwarf galaxy sectors calls for either modification in models employing a constant fraction of halo angular momentum transferred to explain sizes of dwarfs or else points towards our lack of knowledge about dark matter haloes of low-mass galaxies.

Aspherical ULDM collapse: variation in the core–halo mass relation

ABSTRACT Ultralight dark matter (ULDM) is an interesting alternative to the cold dark matter (CDM) paradigm. Due to the extremely low mass of the constituent particle (∼10−22 eV), ULDM can exhibit quantum effects up to kiloparsec scales. In particular, runaway collapse in the centres of ULDM haloes is prevented by quantum pressure, providing a possible resolution to the ‘core-cusp problem’ of CDM. However, the the detailed relationship between the ULDM core mass and that of the overall halo is poorly understood. We simulate the collapse of both spherical and aspherical isolated ULDM overdensities using AxioNyx, finding that the central cores of collapsed haloes undergo sustained oscillatory behaviour, which affects both their peak density and overall morphology. The asphericity of the post-collapse core fluctuates both quantitatively and qualitatively, with oblate initial overdensities generating cores, which fluctuate between prolate and oblate configurations, and more complicated dynamics arising in triaxial scenarios. Furthermore, the peak central densities are higher in spherical configurations. Consequently, astrophysically realistic haloes may exhibit substantial departures from theoretical core–halo profiles and we would expect a significant variance of the properties of haloes with the same mass.

NeutralUniverseMachine: An Empirical Model for the Evolution of H i and H2 Gas in the Universe

Accurately modeling the cold gas content in the universe is challenging for current theoretical models. We propose a new empirical model NeutralUniverseMachine for the evolution of H i and H2 gas along with dark matter halos based on the UniverseMachine catalog. It is able to accurately describe the observed H i and H2 mass functions, molecular-to-atomic ratio, H i–halo mass relation, H i/H2–stellar mass relations at z ∼ 0, as well as the evolution of cosmic gas densities ρ H I and at 0 < z < 6. The predictions from our model include the following: (i) There is weak evolution of H i mass function at 0 < z < 3, but the evolution of H2 mass function is much stronger at the massive end. (ii) The average H i and H2 masses at a given stellar mass decrease by around 1 dex since z = 3 for the star-forming galaxies, but the evolution for the quenched galaxies is much weaker. (iii) Star-forming galaxies have a varying H i depletion time τ H I from 0.1–10 Gyr, and the dependence of τ H I on stellar mass and redshift is much stronger than those of the H2 depletion time. The quenched galaxies have a much longer gas depletion time and weaker redshift evolution. (iv) The cosmic baryon density associated with galaxies is dominated by stars at z < 1.2 and mainly contributed by H i gas at higher redshifts. (v) The H i bias gradually increases with the redshift from 0.69 to 2.33 at 0 < z < 3 and is consistent with recent H i intensity mapping experiments.

The DESI One-Percent Survey: Constructing Galaxy–Halo Connections for ELGs and LRGs Using Auto and Cross Correlations

In the current Dark Energy Spectroscopic Instrument (DESI) survey, emission line galaxies (ELGs) and luminous red galaxies (LRGs) are essential for mapping the dark matter distribution at z ∼ 1. We measure the auto and cross correlation functions of ELGs and LRGs at 0.8 < z ≤ 1.0 from the DESI One-Percent survey. Following Gao et al., we construct the galaxy–halo connections for ELGs and LRGs simultaneously. With the stellar–halo mass relation for the whole galaxy population (i.e., normal galaxies), LRGs can be selected directly by stellar mass, while ELGs can also be selected randomly based on the observed number density of each stellar mass, once the probability P sat of a satellite galaxy becoming an ELG is determined. We demonstrate that the observed small scale clustering prefers a halo mass-dependent P sat model rather than a constant. With this model, we can well reproduce the auto correlations of LRGs and the cross correlations between LRGs and ELGs at r p > 0.1 Mpc h −1. We can also reproduce the auto correlations of ELGs at r p > 0.3 Mpc h −1 (s > 1 Mpc h −1) in real (redshift) space. Although our model has only seven parameters, we show that it can be extended to higher redshifts and reproduces the observed auto correlations of ELGs in the whole range of 0.8 < z ≤ 1.6, which enables us to generate a lightcone ELG mock for DESI. With the above model, we further derive halo occupation distributions for ELGs, which can be used to produce ELG mocks in coarse simulations without resolving subhalos.

Mass Dependence of Galaxy–Halo Alignment in LOWZ and CMASS

We measure the galaxy-ellipticity (GI) correlations for the Sloan Digital Sky Survey Data Release 12 LOWZ and CMASS samples with the shape measurements from the DESI Legacy Imaging Surveys. We model the GI correlations in an N-body simulation with our recent accurate stellar–halo mass relation from the Photometric object Around Cosmic webs (PAC) method. The large data set and our accurate modeling turns out an accurate measurement of the alignment angle between central galaxies and their host halos. We find that the alignment of central elliptical galaxies with their host halos increases monotonically with galaxy stellar mass or host halo mass, which can be well described by a power law for the massive galaxies. We also find that central elliptical galaxies are more aligned with their host halos in LOWZ than in CMASS, which might indicate an evolution of galaxy–halo alignment, though future studies are needed to verify this is not induced by the sample selections. In contrast, central disk galaxies are aligned with their host halos about 10 times more weakly in the GI correlation. These results have important implications for intrinsic alignment (IA) correction in weak lensing studies, IA cosmology, and theory of massive galaxy formation.

LIMFAST. II. Line Intensity Mapping as a Probe of High-redshift Galaxy Formation

The epoch of reionization (EoR) offers a unique window into the dawn of galaxy formation, through which high-redshift galaxies can be studied by observations of both themselves and their impact on the intergalactic medium. Line intensity mapping (LIM) promises to explore cosmic reionization and its driving sources by measuring intensity fluctuations of emission lines tracing the cosmic gas in varying phases. Using LIMFAST, a novel seminumerical tool designed to self-consistently simulate LIM signals of multiple EoR probes, we investigate how building blocks of galaxy formation and evolution theory, such as feedback-regulated star formation and chemical enrichment, might be studied with multitracer LIM during the EoR. On galaxy scales, we show that the star formation law and the feedback associated with star formation can be indicated by both the shape and redshift evolution of LIM power spectra. For a baseline model of metal production that traces star formation, we find that lines highly sensitive to metallicity are generally better probes of galaxy formation models. On larger scales, we demonstrate that inferring ionized bubble sizes from cross-correlations between tracers of ionized and neutral gas requires a detailed understanding of the astrophysics that shape the line luminosity–halo mass relation. Despite various modeling and observational challenges, wide-area, multitracer LIM surveys will provide important high-redshift tests for the fundamentals of galaxy formation theory, especially the interplay between star formation and feedback by accessing statistically the entire low-mass population of galaxies as ideal laboratories, complementary to upcoming surveys of individual sources by new-generation telescopes.

Evolution of the mass relation between supermassive black holes and dark matter halos across the cosmic time

ABSTRACT A positive observational proof suggests that most galaxies contain a central supermassive black hole (SMBH) with mass in the range of 106 M⊙–1010 M⊙. It is suggested that the mass of SMBHs is proportionally related to that of the dark matter (DM) halo, even at z = 6. This implies that these SMBHs could coevolve with the host DM halos. Here, we investigate the mass evolution of SMBHs in a hierarchical structure formation by building halo merger trees using the extended Press–Schechter formalism. An SMBH with a mass that follows various power-law relations with the DM halo mass is assigned as an initial condition. Assuming that the mass growth of all black holes is due to mergers, we obtain the relation between SMBH and DM halo masses at the present epoch. By requiring that the mass of the SMBHs at z = 0 should not be greater than the currently observed SMBH-DM halo mass relation, a lower bound on the mass of the DM halo that can contain a SMBH can be imposed at z = 6 as Mlim &amp;gt; 3.6 × 1010 M⊙ × (1.4 − n)2.3, where n is the power-law index of the SMBH-DM halo mass relation at z = 6. Because we only consider mergers for the mass evolution of SMBHs, this model is simplistic and should underestimate the mass of SMBHs relative to the mass of the DM halo at the present epoch. Our work aims to constrain the SMBH-DM mass relation at z = 6 and not build a new model to explain the observations

Galaxy And Mass Assembly (GAMA): The group H i mass as a function of halo mass

ABSTRACT We determine the atomic hydrogen (H i) to halo mass relation (HIHM) using Arecibo Legacy Fast ALFA survey H i data at the location of optically selected groups from the Galaxy And Mass Assembly (GAMA) survey. We make direct H i detections for 37 GAMA groups. Using H i group spectral stacking of 345 groups, we study the group H i content as a function of halo mass across a halo mass range of 1011–1014.7 M⊙. We also correct our results for Eddington bias. We find that the group H i mass generally rises as a function of halo mass from 1.3% of the halo mass at $10^{11.6} \, \text{M}_\odot$ to 0.4% at $10^{13.7} \, \text{M}_\odot$ with some indication of flattening towards the high-mass end. Despite the differences in optical survey limits, group catalogues, and halo mass estimation methods, our results are consistent with previous group H i-stacking studies. Our results are also consistent with mock observations from shark and IllustrisTNG.

Synergizing 21 cm and submillimetre surveys during reionization: new empirical insights

ABSTRACT We use the latest results from Atacama Large Millimetre/submillimetre Array (ALMA) surveys targeting the ionized carbon [C ii] 158 μm and oxygen [O iii] 88 μm lines, in combination with data-driven predictions for the evolution of neutral hydrogen (H i), to illustrate the prospects for intensity mapping cross-correlations between 21 cm and submillimetre surveys over z ∼ 5 – 7. We work with a data set including the ALPINE and REBELS surveys for [C ii] over z ∼ 4.5 – 7, and ALMA [O iii] detections over z ∼ 6 – 9. The resultant evolution of the [C ii] luminosity–halo mass relation is well described by a double power law at high redshifts, with the best-fitting parameters in good agreement with the results of simulations. The data favour secure detections of the autopower spectrum of [C ii] at all redshifts with an enhanced Fred Young Submillimetre Telescope (FYST)-like configuration. Such an experiment, along with the Murchison Widefield Array (MWA) will be able to measure the 21 cm - [C ii] cross-correlation power with a signal-to-noise ratio of a few tens to a few hundreds. We find that a balloon-borne experiment improving upon the Experiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) should be able to detect the 21 cm - [O iii] cross-correlation with the MWA and the Square Kilometre Array (SKA)-LOW out to z ∼ 7. Our results have implications for constraining the evolution of luminous sources during the mid-to-end stages of reionization.

Inferring dark matter halo properties for H i-selected galaxies

ABSTRACT We set constraints on the dark matter halo mass and concentration of ∼22 000 individual galaxies visible both in $\rm{H}\, {\small I}$ (from the ALFALFA survey) and optical light (from the Sloan Digital Sky Survey). This is achieved by combining two Bayesian models, one for the $\rm{H}\, {\small I}$ line width as a function of the stellar and neutral hydrogen mass distributions in a galaxy using kinematic modelling, and the other for the galaxy’s total baryonic mass using the technique of inverse subhalo abundance matching. We hence quantify the constraining power on halo properties of spectroscopic and photometric observations, and assess their consistency. We find good agreement between the two sets of posteriors, although there is a sizeable population of low-line width galaxies that favour significantly smaller dynamical masses than expected from abundance matching (especially for cuspy halo profiles). Abundance matching provides significantly more stringent bounds on halo properties than the $\rm{H}\, {\small I}$ line width, even with a mass–concentration prior included, although combining the two provides a mean gain of 40 per cent for the sample when fitting an NFW profile. We also use our kinematic posteriors to construct a baryonic mass–halo mass relation, which we find to be near power law, and with a somewhat shallower slope than expected from abundance matching. Our method demonstrates the potential of combining photometric and spectroscopic observations to precisely map out the dark matter distribution at the galaxy scale using upcoming $\rm{H}\, {\small I}$ surveys such as the SKA.

Formation of globular clusters in dwarf galaxies of the Local Group

ABSTRACT The existence of globular clusters (GCs) in a few satellite galaxies, and their absence in majority of dwarf galaxies, present a challenge for models attempting to understand the origins of GCs. In addition to GC presence appearing stochastic and difficult to describe with average trends, in the smallest satellite galaxies GCs contribute a substantial fraction of total stellar mass. We investigate the stochasticity and number of GCs in dwarf galaxies using an updated version of our model that links the formation of GCs to the growth of the host galaxy mass. We find that more than 50 per cent of dwarf galaxies with stellar mass $M_{\star }\lesssim 2\times 10^7\, \mathrm{M}_\odot$ do not host GCs, whereas dwarfs with $M_{\star }\sim 10^8\, \mathrm{M}_\odot$ almost always contain some GCs, with a median number ∼10 at z = 0. These predictions are in agreement with the observations of the Local Volume dwarfs. We also confirm the near-linear GC system mass–halo mass relation down to $M_{\mathrm{h}}\simeq 10^8\, \mathrm{M}_\odot$ under the assumption that GC formation and evolution in galaxies of all mass can be described by the same physical model. A detailed case study of two model dwarfs that resemble the Fornax dwarf spheroidal galaxy shows that observational samples can be notably biased by incompleteness below detection limit and at large radii.

Evidence for a Massive Andromeda Galaxy Using Satellite Galaxy Proper Motions

We present new mass estimates for Andromeda (M31) using the orbital angular momenta of four satellite galaxies (M33, NGC 185, NGC 147, and IC 10) derived from existing proper motions, distances, and line-of-sight velocities. We infer two masses for M31: using satellite galaxy phase-space information derived with Hubble Space Telescope (HST)-based M31 proper motions and using phase-space information derived with the weighted average of HST+Gaia-based M31 proper motions. The precision of our new M31 mass estimates (23%–50%) improves by a factor of two compared to previous mass estimates using a similar methodology with just one satellite galaxy, and places our results among the highest-precision M31 estimates in recent literature. Furthermore, our results are consistent with recently revised estimates for the total mass of the Local Group (LG), with the stellar mass–halo mass relation, and with observed kinematic data for both M31 and its entire population of satellites. An M31 mass >2.5 × 1012 M ⊙ could have major implications for our understanding of LG dynamics, M31's merger and accretion history, and our understanding of LG galaxies in a cosmological context.

Effects of feedback on galaxies in the VELA simulations: elongation, clumps, and compaction

ABSTRACT The evolution of star-forming galaxies at high redshifts is very sensitive to the strength and nature of stellar feedback. Using two sets of cosmological, zoom-in simulations from the VELA suite, we compare the effects of two different models of feedback: with and without kinetic feedback from the expansion of supernovae shells and stellar winds. At a fixed halo mass and redshift, the stellar mass is reduced by a factor of ∼1–3 in the models with stronger feedback, so the stellar mass–halo mass relation is in better agreement with abundance matching results. On the other hand, the three-dimensional shape of low-mass galaxies is elongated along a major axis in both models. At a fixed stellar mass, M* &amp;lt; 1010 M⊙, galaxies are more elongated in the strong-feedback case. More massive, star-forming discs with high surface densities form giant clumps. However, the population of round, compact, old (agec &amp;gt; 300 Myr), quenched, stellar (or gas-poor) clumps is absent in the model with strong feedback. On the other hand, giant star-forming clumps with intermediate ages (agec = 100–300 Myr) can survive for several disc dynamical times, independently of feedback strength. The evolution through compaction followed by quenching in the plane of central surface density and specific star formation rate is similar under the two feedback models.