Tidal Stripping Research Articles

Magellanic Mayhem: Metallicities and Motions

Abstract We assemble a catalog of Magellanic Cloud red giants from Data Release 2 of the Gaia mission and, utilizing machine-learning methods, obtain photometric metallicity estimates for them. In doing so, we are able to chemically map the entirety of the Magellanic System at once. Our maps reveal a plethora of substructure within our red giant sample, with the Large Magellanic Cloud (LMC) bar and spiral arm being readily apparent. We uncover a curious spiral-like feature in the southern portion of the LMC disk, hosting relatively metal-rich giants and likely a by-product of historic encounters with the Small Magellanic Cloud (SMC). Modeling the LMC as an inclined thin disk, we find a shallow metallicity gradient of −0.048 ± 0.001 dex kpc−1 out to ∼12° from the center of the dwarf. We see evidence that the SMC is disrupting, with its outer isodensity contours displaying the S-shape symptomatic of tidal stripping. On studying the proper motions of the SMC giants, we observe a population of them being violently dragged toward the larger Cloud. The perturbed stars predominantly lie in front of the SMC, and we interpret that they exist as a tidal tail of the dwarf, trailing in its motion and undergoing severe disruption from the LMC. We find the metallicity structure in the Magellanic Bridge region to be complex, with evidence for a composite nature in this stellar population, consisting of both LMC and SMC debris.

Constraining velocity-dependent self-interacting dark matter with the Milky Way’s dwarf spheroidal galaxies

ABSTRACT The observed anticorrelation between the central dark matter (DM) densities of the bright Milky Way (MW) dwarf spheroidal galaxies (dSphs) and their orbital pericentre distances poses a potential signature of self-interacting dark matter (SIDM). In this work, we investigate this possibility by analysing the range of SIDM scattering cross-section per unit mass, σ/mχ, able to explain such anticorrelation. We simulate the orbital evolution of dSphs subhaloes around the MW assuming an analytical form for the gravitational potential, adopting the proper motions from the Gaia mission and including a consistent characterization of gravitational tidal stripping. The evolution of subhalo density profiles is modelled using the gravothermal fluid formalism, where DM particle collisions induce thermal conduction that depends on σ/mχ. We find that models of dSphs, such as Carina and Fornax, reproduce the observed central DM densities with fixed σ/mχ ranging between 30 and 50 cm2 g−1, whereas other dSphs prefer larger values ranging between 70 and 100 cm2 g−1. These cross-sections correlate with the average collision velocity of DM particles within each subhalo’s core, so that systems modelled with large cross-sections have lower collision velocities. We fit the cross-section–velocity correlation with a SIDM particle model, where a DM particle of mass mχ = 53.93 ± 9.81 GeV interacts under the exchange of a light mediator of mass mϕ = 6.6 ± 0.43 MeV, with the self-interactions being described by a Yukawa potential. The outcome is a cross-section–velocity relation that explains the diverse DM profiles of MW dSph satellites and is consistent with observational constraints on larger scales.

Evolution of subhalo orbits in a smoothly growing host halo potential

ABSTRACT The orbital parameters of dark matter (DM) subhaloes play an essential role in determining their mass-loss rates and overall spatial distribution within a host halo. Haloes in cosmological simulations grow by a combination of relatively smooth accretion and more violent mergers, and both processes will modify subhalo orbits. To isolate the impact of the smooth growth of the host halo from other relevant mechanisms, we study subhalo orbital evolution using numerical calculations in which subhaloes are modelled as massless particles orbiting in a time-varying spherical potential. We find that the radial action of the subhalo orbit decreases over the first few orbits, indicating that the response to the growth of the host halo is not adiabatic during this phase. The subhalo orbits can shrink by a factor of ∼1.5 in this phase. Subsequently, the radial action is well conserved and orbital contraction slows down. We propose a model accurately describing the orbital evolution. Given these results, we consider the spatial distribution of the population of subhaloes identified in high-resolution cosmological simulations. We find that it is consistent with this population having been accreted at $z \lesssim 3$, indicating that any subhaloes accreted earlier are unresolved in the simulations. We also discuss tidal stripping as a formation scenario for NGC 1052-DF2, an ultra diffuse galaxy significantly lacking DM, and find that its expected DM mass could be consistent with observational constraints if its progenitor was accreted early enough, $z \gtrsim 1.5$, although it should still be a relatively rare object.

The kinematics of globular cluster populations in the E-MOSAICS simulations and their implications for the assembly history of the Milky Way

ABSTRACT We present a detailed comparison of the Milky Way (MW) globular cluster (GC) kinematics with the 25 MW-mass cosmological simulations from the E-MOSAICS project. While the MW falls within the kinematic distribution of GCs spanned by the simulations, the relative kinematics of its metal-rich ($[\rm {Fe}/\rm {H}] \gt -1.2$) versus metal-poor ($[\rm {Fe}/\rm {H}] \lt -1.2$) and inner (r < 8 kpc) versus outer (r > 8 kpc) populations are atypical for its mass. To understand the origins of these features, we perform a comprehensive statistical analysis of the simulations, and find 18 correlations describing the assembly of L* galaxies and their dark matter haloes based on their GC population kinematics. The correlations arise because the orbital distributions of accreted and in situ GCs depend on the masses and accretion redshifts of accreted satellites, driven by the combined effects of dynamical fraction, tidal stripping, and dynamical heating. Because the kinematics of in situ/accreted GCs are broadly traced by the metal-rich/metal-poor and inner/outer populations, the observed GC kinematics are a sensitive probe of galaxy assembly. We predict that relative to the population of L* galaxies, the MW assembled its dark matter and stellar mass rapidly through a combination of in situ star formation, more than a dozen low-mass mergers, and 1.4 ± 1.2 early ($z$ = 3.1 ± 1.3) major mergers. The rapid assembly period ended early, limiting the fraction of accreted stars. We conclude by providing detailed quantitative predictions for the assembly history of the MW.

Black Hole Mergers from Star Clusters with Top-heavy Initial Mass Functions

Abstract Recent observations of globular clusters (GCs) provide evidence that the stellar initial mass function (IMF) may not be universal, suggesting specifically that the IMF grows increasingly top-heavy with decreasing metallicity and increasing gas density. Noncanonical IMFs can greatly affect the evolution of GCs, mainly because the high end determines how many black holes (BHs) form. Here we compute a new set of GC models, varying the IMF within observational uncertainties. We find that GCs with top-heavy IMFs lose most of their mass within a few gigayears through stellar winds and tidal stripping. Heating of the cluster through BH mass segregation greatly enhances this process. We show that, as they approach complete dissolution, GCs with top-heavy IMFs can evolve into “dark clusters” consisting of mostly BHs by mass. In addition to producing more BHs, GCs with top-heavy IMFs also produce many more binary BH (BBH) mergers. Even though these clusters are short-lived, mergers of ejected BBHs continue at a rate comparable to, or greater than, what is found for long-lived GCs with canonical IMFs. Therefore, these clusters, though they are no longer visible today, could still contribute significantly to the local BBH merger rate detectable by LIGO/Virgo, especially for sources with higher component masses well into the BH mass gap. We also report that one of our GC models with a top-heavy IMF produces dozens of intermediate-mass black holes (IMBHs) with masses , including one with . Ultimately, additional gravitational wave observations will provide strong constraints on the stellar IMF in old GCs and the formation of IMBHs at high redshift.

Dark matter-deficient dwarf galaxies form via tidal stripping of dark matter in interactions with massive companions

ABSTRACT In the standard ΛCDM (Lambda cold dark matter) paradigm, dwarf galaxies are expected to be dark matter-rich, as baryonic feedback is thought to quickly drive gas out of their shallow potential wells and quench star formation at early epochs. Recent observations of local dwarfs with extremely low dark matter content appear to contradict this picture, potentially bringing the validity of the standard model into question. We use NewHorizon, a high-resolution cosmological simulation, to demonstrate that sustained stripping of dark matter, in tidal interactions between a massive galaxy and a dwarf satellite, naturally produces dwarfs that are dark matter-deficient, even though their initial dark matter fractions are normal. The process of dark matter stripping is responsible for the large scatter in the halo-to-stellar mass relation in the dwarf regime. The degree of stripping is driven by the closeness of the orbit of the dwarf around its massive companion and, in extreme cases, produces dwarfs with halo-to-stellar mass ratios as low as unity, consistent with the findings of recent observational studies. ∼30 per cent of dwarfs show some deviation from normal dark matter fractions due to dark matter stripping, with 10 per cent showing high levels of dark matter deficiency (Mhalo/M⋆ < 10). Given their close orbits, a significant fraction of dark matter-deficient dwarfs merge with their massive companions (e.g. ∼70 per cent merge over time-scales of ∼3.5 Gyr), with the dark matter-deficient population being constantly replenished by new interactions between dwarfs and massive companions. The creation of these galaxies is therefore a natural by-product of galaxy evolution and their existence is not in tension with the standard paradigm.

A fully general, non-perturbative treatment of impulsive heating

ABSTRACT Impulsive encounters between astrophysical objects are usually treated using the distant tide approximation (DTA) for which the impact parameter, b, is assumed to be significantly larger than the characteristic radii of the subject, rS, and the perturber, rP. The perturber potential is then expanded as a multipole series and truncated at the quadrupole term. When the perturber is more extended than the subject, this standard approach can be extended to the case where rS ≪ b < rP. However, for encounters with b of order rS or smaller, the DTA typically overpredicts the impulse, Δv, and hence the internal energy change of the subject, ΔEint. This is unfortunate, as these close encounters are the most interesting, potentially leading to tidal capture, mass stripping, or tidal disruption. Another drawback of the DTA is that ΔEint is proportional to the moment of inertia, which diverges unless the subject is truncated or has a density profile that falls off faster than r−5. To overcome these shortcomings, this paper presents a fully general, non-perturbative treatment of impulsive encounters which is valid for any impact parameter, and not hampered by divergence issues, thereby negating the necessity to truncate the subject. We present analytical expressions for Δv for a variety of perturber profiles, apply our formalism to both straight-path encounters and eccentric orbits, and discuss the mass-loss due to tidal shocks in gravitational encounters between equal-mass galaxies.

Ultrafaint Dwarfs in a Milky Way Context: Introducing the Mint Condition DC Justice League Simulations

Abstract We present results from the “Mint” resolution DC Justice League suite of Milky Way–like zoom-in cosmological simulations, which extend our study of nearby galaxies down into the ultrafaint dwarf (UFD) regime for the first time. The mass resolution of these simulations is the highest ever published for cosmological Milky Way zoom-in simulations run to z = 0, with initial star (dark matter) particle masses of 994 (17900) M ⊙, and a force resolution of 87 pc. We study the surrounding dwarfs and UFDs, and find that the simulations match the observed dynamical properties of galaxies with −3 > M V > −19, and reproduce the scatter seen in the size–luminosity plane for r h ≳ 200 pc. We predict the vast majority of nearby galaxies will be observable by the Vera Rubin Observatory’s coadded Legacy Survey of Space and Time. We additionally show that faint dwarfs with velocity dispersions ≲5 km s−1 result from severe tidal stripping of the host halo. We investigate the quenching of UFDs in a hydrodynamical Milky Way context and find that the majority of UFDs are quenched prior to interactions with the Milky Way, though some of the quenched UFDs retain their gas until infall. Additionally, these simulations yield some unique dwarfs that are the first of their kind to be simulated, e.g., an H i-rich field UFD, a late-forming UFD that has structural properties similar to Crater 2, as well as a compact dwarf satellite that has no dark matter at z = 0.

YZiCS: On the Mass Segregation of Galaxies in Clusters

Abstract Mass segregation, a tendency for more massive galaxies to be distributed closer to the cluster center, is naturally expected from dynamical friction, but its presence is still controversial. Using deep optical observations of 14 Abell clusters (KYDISC) and a set of hydrodynamic simulations (YZiCS), we find in some cases a hint of mass segregation inside the virial radius. Segregation is visible more clearly when the massive galaxy fraction is used instead of mean stellar mass. The trend is more significant in the simulations than in the observations. To find out the mechanisms affecting mass segregation, we look into the evolution of individual simulated clusters. We find that the degree of mass segregation is different for different clusters: the trend is visible only for low-mass clusters. We compare the masses of galaxies and their dark halos at the time of infall and at the present epoch to quantify the amount of tidal stripping. We then conclude that satellites that get accreted at earlier epochs, or galaxies in more massive clusters, go through more tidal stripping. These combined effects result in a correlation between the host halo mass and the degree of stellar mass segregation.

Discovery of a Young Stellar Snake with Two Dissolving Cores in the Solar Neighborhood

Abstract We report the discovery of a young (only 30–40 Myr) snake-like structure (dubbed a stellar snake) in the solar neighborhood from Gaia DR2. The average distance of this structure is about 310 pc from us. Both the length and width are over 200 pc, but the thickness is only about 80 pc. The snake has one tail and two dissolving cores, which can be clearly distinguished in the 6D phase space. The whole structure includes thousands of members with a total mass of larger than 2000 M ⊙ in a uniform population. The population is so young that it cannot be well explained with the classical theory of tidal tails. We therefore suspect that the snake is hierarchically primordial, rather than the result of dynamically tidal stripping, even if the snake is probably expanding. The coherent 5D phase information and the ages suggest that the snake was probably born in the same environment as the filamentary structure of Beccari et al. If so, the snake could extend the sky region of the Vela OB2 association by a factor of ∼2 and supplement the census of its coeval structures. This finding is useful to understanding the history of the formation and evolution of the Vela OB2 complex. The age of the snake well matches with that of the Gould Belt. In the sky region of our interest, we detect one new open cluster, which is named Tian 1 in this work.

The Galaxy “Missing Dark Matter” NGC 1052-DF4 is Undergoing Tidal Disruption

Abstract The existence of long-lived galaxies lacking dark matter represents a challenge to our understanding of how galaxies form. Here, we present evidence that explains the lack of dark matter in one such galaxy: NGC 1052-DF4. Deep optical imaging of the system has detected tidal tails in this object caused by its interaction with its neighboring galaxy NGC 1035. As stars are more centrally concentrated than dark matter, tidal stripping will remove a significant percentage of dark matter before affecting the stars of the galaxy. Only of the stellar mass of the galaxy is in the tidal tails, suggesting that the stars of NGC 1052-DF4 are only now starting to be affected by the interaction, while the percentage of remaining dark matter is . This naturally explains the low content of dark matter inferred for this galaxy and reconciles these types of galaxies with our current models of galaxy formation.

Probing the nature of dark matter with accreted globular cluster streams

ABSTRACT The steepness of the central density profiles of dark matter (DM) in low-mass galaxy haloes (e.g. dwarf galaxies) is a powerful probe of the nature of DM. We propose a novel scheme to probe the inner profiles of galaxy subhaloes using stellar streams. We show that the present-day morphological and dynamical properties of accreted globular cluster (GC) streams – those produced from tidal stripping of GCs that initially evolved within satellite galaxies and later merged with the Milky Way (MW) – are sensitive to the central DM density profile and mass of their parent satellites. GCs that accrete within cuspy cold dark matter (CDM) subhaloes produce streams that are physically wider and dynamically hotter than streams that accrete inside cored subhaloes. A first comparison of MW streams ‘GD-1’ and ‘Jhelum’ (likely of accreted GC origin) with our simulations indicates a preference for cored subhaloes. If these results hold up in future data, the implication is that either the DM cusps were erased by baryonic feedback, or their subhaloes naturally possessed cored density profiles implying particle physics models beyond CDM. Moreover, accreted GC streams are highly structured and exhibit complex morphological features (e.g. parallel structures and ‘spurs’). This implies that the accretion scenario can naturally explain the recently observed peculiarities in some of the MW streams. We also propose a novel mechanism for forming ‘gaps’ in stellar streams when the remnant of the parent subhalo (which hosted the GC) later passes through the GC stream. This encounter can last a longer time (and have more of an impact) than the random encounters with DM subhaloes previously considered, because the GC stream and its parent subhalo are on similar orbits with small relative velocities. Current and future surveys of the MW halo will uncover numerous faint stellar streams and provide the data needed to substantiate our preliminary tests with this new probe of DM.

The distinct stellar-to-halo mass relations of satellite and central galaxies: insights from the IllustrisTNG simulations

ABSTRACT We study the stellar-to-halo mass relation (SHMR) for central and satellite galaxies with total dynamical masses above $10^{10.5}\, \rm {M}_\odot$ using the suite of cosmological magnetohydrodynamical simulations IllustrisTNG. In particular, we quantify environmental effects on satellite populations from TNG50, TNG100, and TNG300 located within the virial radius of group- and cluster-like hosts with total masses of $10^{12\!-\!15.2}\, \rm {M}_\odot$. At fixed stellar mass, the satellite SHMR exhibits a distinct shift towards lower dynamical mass compared to the SHMR of centrals. Conversely, at fixed dynamical mass, satellite galaxies appear to have larger stellar-to-total mass fractions than centrals by up to a factor of a few. The systematic deviation from the central SHMR is larger for satellites in more massive hosts, at smaller cluster-centric distances, with earlier infall times, and that inhabits higher local density environments; moreover, it is in place already at early times (z ≲ 2). Systematic environmental effects might contribute to the perceived galaxy-to-galaxy variation in the measured SHMR when galaxies cannot be separated into satellites and centrals. The SHMR of satellites exhibits a larger scatter than centrals (by up to ∼0.8 dex), over the whole range of dynamical mass. The shift of the satellite SHMR results mostly from tidal stripping of their dark matter, which affects satellites in an outside-in fashion: The departure of the satellite SHMR from the centrals’ relation diminishes for measurements of dynamical mass in progressively smaller apertures. Finally, we provide a family of fitting functions for the SHMR predicted by IllustrisTNG.

Environmental processing of galaxies in H i-rich groups

ABSTRACT We present and explore the resolved atomic hydrogen (H i) content of 13 H i-rich and late-type dominated groups denoted ‘Choirs’. We quantify the H i content of the Choir galaxies with respect to the median of the H i-mass fraction ($f_{\rm{{H {\small I}}}}$) of their grandparent H i Parkes All Sky Survey (HIPASS) sample. We find that the H i-mass fraction of the Choir galaxies is dispersed around the HIPASS median in the range $-1.4\le \Delta f_{\rm{{H {\small I}}}}\textrm{[dex]}\le$ 0.7, from H i-excess to H i-deficient galaxy regime. The H i-excess/H i-deficient galaxies contain more/less than 2.5 times their expected H i content with respect to the HIPASS median. We show and discuss that the environmental processing in Choirs occurs via tidal stripping and galaxy mergers. Our analysis suggests that tidal stripping contributes to the loss of the H i, while galaxy mergers contribute to the enhancement of the H i. Exploring the mid-infrared properties of Choir galaxies, we find possible environmental processing in only nine Choir galaxies, which indicates that environmental processing is more perceptible in the H i content than the mid-infrared properties. Moreover, we find that environmental processing occurs in Choir groups regardless of their global environment, whether they are in isolation or in proximity to the denser structures, such as cosmic web filaments. We explore possible scenarios of the Choirs evolution, taking into account their H i content, velocity dispersion, crossing time, and their global environment. We conclude that the most likely evolution for the majority of Choir groups is that they will become more compact as their members undergo multiple H i-rich mergers.

Depletion of Bright Red Giants in the Galactic Center during Its Active Phases

Abstract Observations in the near-infrared domain showed the presence of the flat core of bright late-type stars inside ∼0.5 pc from the Galactic center supermassive black hole (Sgr A*), while young massive OB/Wolf–Rayet stars form a cusp. Several dynamical processes were proposed to explain this apparent paradox of the distribution of the Galactic center stellar populations. Given the mounting evidence on the significantly increased activity of Sgr A* during the past million years, we propose a scenario based on the interaction between the late-type giants and a nuclear jet, whose past existence and energetics can be inferred from the presence of γ-ray Fermi bubbles and bipolar radio bubbles. Extended, loose envelopes of red giant stars can be ablated by the jet with kinetic luminosity in the range of L j ≈ 1041– within the inner ∼0.04 pc of Sgr A* (S-cluster region), which would lead to their infrared luminosity decrease after several thousand jet–star interactions. The ablation of the atmospheres of red giants is complemented by the process of tidal stripping that operates at distances of ≲1 mpc, and by the direct mechanical interaction of stars with a clumpy disk at ≳0.04 pc, which can explain the flat density profile of bright late-type stars inside the inner half parsec from Sgr A*.

Extracting galaxy merger time-scales II: a new fitting formula

ABSTRACT Predicting the merger time-scale (τmerge) of merging dark matter haloes, based on their orbital parameters and the structural properties of their hosts, is a fundamental problem in gravitational dynamics that has important consequences for our understanding of cosmological structure formation and galaxy formation. Previous models predicting τmerge have shown varying degrees of success when compared to the results of cosmological N-body simulations. We build on this previous work and propose a new model for τmerge that draws on insights derived from these simulations. We find that published predictions can provide reasonable estimates for τmerge based on orbital properties at infall, but tend to underpredict τmerge inside the host virial radius (R200) because tidal stripping is neglected, and overpredict it outside R200 because the host mass is underestimated. Furthermore, we find that models that account for orbital angular momentum via the circular radius Rcirc underpredict (overpredict) τmerge for bound (unbound) systems. By fitting for the dependence of τmerge on various orbital and host halo properties, we derive an improved model for τmerge that can be applied to a merging halo at any point in its orbit. Finally, we discuss briefly the implications of our new model for τmerge for semi-analytical galaxy formation modelling.

Joint gas and stellar dynamical models of WLM: an isolated dwarf galaxy within a cored, prolate DM halo

ABSTRACT We present multitracer dynamical models of the low-mass (M* ∼ 107), isolated dwarf irregular galaxy WLM in order to simultaneously constrain the inner slope of the dark matter (DM) halo density profile (γ) and flattening (qDM), and the stellar orbital anisotropy (βz, βr). For the first time, we show how jointly constraining the mass distribution from the H i gas rotation curve and solving the Jeans equations with discrete stellar kinematics lead to a factor of ∼2 reduction in the uncertainties on γ. The mass-anisotropy degeneracy is also partially broken, leading to reductions on uncertainty by ${\sim} 30{{\ \rm per\ cent}}$ on Mvir (and ${\sim} 70{{\ \rm per\ cent}}$ at the half-light radius) and ${\sim} 25{{\ \rm per\ cent}}$ on anisotropy. Our inferred value of γ = 0.3 ± 0.1 is robust to the halo geometry, and in excellent agreement with predictions of stellar feedback-driven DM core creation. The derived prolate geometry of the DM halo with qDM = 2 ± 1 is consistent with Lambda cold dark matter simulations of dwarf galaxy haloes. While self-interacting DM (SIDM) models with σ/mX ∼ 0.6 can reproduce this cored DM profile, the interaction events may sphericalize the halo. The simultaneously cored and prolate DM halo may therefore present a challenge for SIDM. Finally, we find that the radial profile of stellar anisotropy in WLM (βr) follows a nearly identical trend of increasing tangential anisotropy to the classical dwarf spheroidals, Fornax and Sculptor. Given WLM’s orbital history, this result may call into question whether such anisotropy is a consequence of tidal stripping in only one pericentric passage or if it instead is a feature of the largely self-similar formation and evolutionary pathways for some dwarf galaxies.

A new calibration method of sub-halo orbital evolution for semi-analytic models

ABSTRACT Understanding the non-linear dynamics of satellite haloes (a.k.a. ‘sub-haloes’) is important for predicting the abundance and distribution of dark matter sub-structures and satellite galaxies, and for distinguishing among microphysical dark matter models using observations. Typically, modelling these dynamics requires large N-body simulations with high resolution. Semi-analytic models can provide a more efficient way to describe the key physical processes such as dynamical friction, tidal mass loss, and tidal heating, with only a few free parameters. In this work, we present a fast Markov chain Monte Carlo fitting approach to explore the parameter space of such a sub-halo non-linear evolution model. We use the dynamical models described in an earlier work and calibrate the models to two sets of high-resolution cold dark matter N-body simulations, ELVIS and Caterpillar. Compared to previous calibrations that used manual parameter tuning, our approach provides a more robust way to determine the best-fitting parameters and their posterior probabilities. We find that jointly fitting for the sub-halo mass and maximum velocity functions can break the degeneracy between tidal stripping and tidal heating parameters, as well as providing better constraints on the strength of dynamical friction. We show that our semi-analytic simulation can accurately reproduce N-body simulations statistics, and that the calibration results for the two sets of N-body simulations agree at 95 per cent confidence level. Dynamical models calibrated in this work will be important for future dark matter sub-structure studies.

The baryon content of groups and clusters of galaxies in the FABLE simulations

ABSTRACT We study the gas and stellar mass content of galaxy groups and clusters in the fable suite of cosmological hydrodynamical simulations, including the evolution of their central brightest cluster galaxies (BCGs), satellite galaxies, and intracluster light (ICL). The total gas and stellar mass of fable clusters are in good agreement with observations and show negligible redshift evolution at fixed halo mass for $M_{500} \gtrsim 3 \times 10^{14} \, \mathrm{M}_{\odot }$ at z ≲ 1, in line with recent findings from Sunyaev–Zel’dovich (SZ)-selected cluster samples. Importantly, the simulations predict significant redshift evolution in these quantities in the low-mass ($M_{500} \sim 10^{14} \, \mathrm{M}_{\odot }$) regime, which will be testable with upcoming SZ surveys such as SPT-3G. Whilst the stellar masses of fable BCGs are in reasonable agreement with observations, the total stellar mass in satellite galaxies is lower than observed and the total mass in ICL is somewhat higher. This may be caused by enhanced tidal stripping of satellite galaxies due to their large sizes. BCGs are characterized by moderate stellar mass growth at z < 1 coincident with a late-time development of the ICL. The level of BCG mass growth is in good agreement with recent observations; however, we caution that the inferred growth depends sensitively on the mass definition. We further show that in situ star formation contributes more than half the mass of a BCG over its lifetime, the bulk of which is gained at z > 1 where star formation rates are highest. The stellar mass profiles of the BCG+ICL component are similar to observed profiles out to ∼100 kpc at z ≈ 0 and follow a close to power law shape out to several hundred kpc. We further demonstrate that the inferred size growth of BCGs can be severely biased by the choice of parametric model and the outer radius of the fit.

Self-Interacting Dark Matter and the Origin of Ultradiffuse Galaxies NGC1052-DF2 and -DF4.

Observations of ultradiffuse galaxies NGC 1052-DF2 and -DF4 show they may contain little dark matter, challenging our understanding of galaxy formation. Using controlled N-body simulations, we explore the possibility that their properties can be reproduced through tidal stripping from the elliptical galaxy NGC 1052, in both cold dark matter (CDM) and self-interacting dark matter (SIDM) scenarios. To explain the dark matter deficiency, we find that a CDM halo must have a very low concentration so that it can lose sufficient inner mass in the tidal field. In contrast, SIDM favors a higher and more reasonable concentration as core formation enhances tidal mass loss. Final stellar distributions in our SIDM benchmarks are more diffuse than the CDM one, and hence the former are in better agreement with the data. We further show that a cored CDM halo model modified by strong baryonic feedback is unlikely to reproduce the observations. Our results indicate that SIDM is more favorable for the formation of dark-matter-deficient galaxies.