Tidal Stripping Research Articles

The diversity of core–halo structure in the fuzzy dark matter model

ABSTRACT In the fuzzy dark matter (FDM) model, gravitationally collapsed objects always consist of a solitonic core located within a virialized halo. Although various numerical simulations have confirmed that the collapsed structure can be described by a cored Navarro–Frenk–White-like density profile, there is still disagreement about the relation between the core mass and the halo mass. To fully understand this relation, we have assembled a large sample of cored haloes based on both idealized soliton mergers and cosmological simulations with various box sizes. We find that there exists a sizeable dispersion in the core–halo mass relation that increases with halo mass, indicating that the FDM model allows cores and haloes to coexist in diverse configurations. We provide a new empirical equation for a core–halo mass relation with uncertainties that can encompass all previously found relations in the dispersion, and emphasize that any observational constraints on the particle mass m using a tight one-to-one core–halo mass relation should suffer from an additional uncertainty of the order of 50 per cent for halo masses ${\gtrsim} 10^9 \, [8\times 10^{-23} \, \mathrm{eV}/(mc^2)]^{3/2} \, \mathrm{M}_\odot$. We suggest that tidal stripping may be one of the effects contributing to the scatter in the relation.

On the tidal formation of dark matter-deficient galaxies

ABSTRACT Previous studies have shown that dark matter-deficient galaxies (DMDG) such as NGC 1052-DF2 (hereafter DF2) can result from tidal stripping. An important question, though, is whether such a stripping scenario can explain DF2’s large specific frequency of globular clusters (GCs). After all, tidal stripping and shocking preferentially remove matter from the outskirts. We examine this using idealized, high-resolution simulations of a regular dark matter-dominated galaxy that is accreted on to a massive halo. As long as the initial (pre-infall) dark matter halo of the satellite is cored, which is consistent with predictions of cosmological, hydrodynamical simulations, the tidal remnant can be made to resemble DF2 in all its properties, including its GC population. The required orbit has a pericentre at the 8.3 percentile of the distribution for subhaloes at infall, and thus is not particularly extreme. On this orbit the satellite loses 98.5 (30) per cent of its original dark matter (stellar) mass, and thus evolves into a DMDG. The fraction of GCs that is stripped off depends on the initial radial distribution. If, at infall, the median projected radius of the GC population is roughly two times that of the stars, consistent with observations of isolated galaxies, only ∼20 per cent of the GCs are stripped off. This is less than for the stars, which is due to dynamical friction counteracting the tidal stirring. We predict that, if indeed DF2 was crafted by strong tides, its stellar outskirts should have a very shallow metallicity gradient.

Drivers of asymmetry in synthetic H i emission-line profiles of galaxies in the eagle simulation

ABSTRACT We study the shapes of spatially integrated $\rm{H}\, \small {{I}}$ emission-line profiles of galaxies in the eagle simulation using three separate measures of the profile’s asymmetry. We show that the subset of eagle galaxies whose gas fractions and stellar masses are consistent with those in the xGASS survey also have similar $\rm{H}\, \small {{I}}$ line asymmetries. Central galaxies with symmetric $\rm{H}\, \small {{I}}$ line profiles typically correspond to rotationally supported $\rm{H}\, \small {{I}}$ and stellar discs, but those with asymmetric line profiles may or may not correspond to dispersion-dominated systems. Galaxies with symmetric $\rm{H}\, \small {{I}}$ emission lines are, on average, more gas rich than those with asymmetric lines, and also exhibit systematic differences in their specific star formation rates, suggesting that turbulence generated by stellar or AGN feedback may be one factor contributing to $\rm{H}\, \small {{I}}$ line asymmetry. The line asymmetry also correlates strongly with the dynamical state of a galaxy’s host dark matter halo: older, more relaxed haloes host more-symmetric galaxies than those hosted by unrelaxed ones. At fixed halo mass, asymmetric centrals tend to be surrounded by a larger number of massive subhaloes than their symmetric counterparts, and also experience higher rates of gas accretion and outflow. At fixed stellar mass, central galaxies have, on average, more symmetric $\rm{H}\, \small {{I}}$ emission lines than satellites; for the latter, ram pressure and tidal stripping are significant sources of asymmetry.

Tracking the orbit of unresolved subhaloes for semi-analytic models

ABSTRACTWe present a model to track the orbital evolution of ‘unresolved subhaloes’ (USHs) in cosmological simulations. USHs are subhaloes that are no longer distinguished by halo finders as self-bound overdensities within their larger host system due to limited mass resolution. These subhaloes would host ‘orphan galaxies’ in semi-analytic models of galaxy formation and evolution (SAMs). Predicting the evolution of the phase-space components of USHs is crucial for the adequate modelling of environmental processes, interactions, and mergers implemented in SAMs that affect the baryonic properties of orphan satellites. Our model takes into account dynamical friction drag, mass-loss by tidal stripping and merger with the host halo, involving three free parameters. To calibrate this model, we consider two DM-only simulations of different mass resolution (MultiDark simulations). The simulation with higher mass resolution (smdpl; $m_{\rm DM} = 9.6 \times 10^7\, h^{-1}\, \mathrm{M_{\odot }}$) provides information about subhaloes that are not resolved in the lower mass resolution one (mdpl2; $m_{\rm DM} = 1.5 \times 10^9\, h^{-1}\, \mathrm{M_{\odot }}$); the orbit of those USHs is tracked by our model. We use as constraining functions the subhalo mass function (SHMF) and the two-point correlation function (2PCF) obtained from smdpl, being the latter a novel aspect of our approach. While the SHMF fails to put tight constraints on the efficiency of dynamical friction and the merger condition, the addition of clustering information helps us to specify the parameters of the model related to the spatial distribution of subhaloes. Our model allows to achieve good convergence between the results of simulations of different mass resolution, with a precision better than 10 per cent for both SHMF and 2PCF.

Modifying PyUltraLight to model scalar dark matter with self-interactions

We introduce a modification of the pysiultralight code that models the dynamical evolution of ultralight axionlike scalar dark matter fields. Our modified code, pysiultralight, adds a quartic, self-interaction term to reflect the one which arises naturally in axionlike particle models. Using a particle mass of ${10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}/{\mathrm{c}}^{2}$, we show that pysiultralight produces spatially oscillating solitons, exploding solitons, and collapsing solitons which prior analytic work shows will occur with attractive self-interactions. Using our code we calculate the oscillation frequency as a function of soliton mass and equilibrium radius in the presence of attractive self-interactions. We show that when the soliton mass is below the critical mass (${M}_{c}=\frac{\sqrt{3}}{2}{M}_{\mathrm{max}}$) described by Chavanis [Phys. Rev. D 94, 083007 (2016)] and the initial radius is within a specific range, solitons are unstable and explode. We test the maximum mass criteria described by Chavanis [Phys. Rev. D 94, 083007 (2016)] and Chavanis and Delfini [Phys. Rev. D 84, 043532 (2011)] for a soliton to collapse when attractive self-interactions are included. We also analyze both binary soliton collisions and a soliton rotating around a central mass with attractive and repulsive self-interactions. We find that when attractive self-interactions are included, the density profiles get distorted after a binary collision. We also find that a soliton is less susceptible to tidal stripping when attractive self-interactions are included. We find that the opposite is true for repulsive self-interactions in that solitons would be more easily tidally stripped. Including self-interactions might therefore influence the survival timescales of infalling solitons.

The tidal evolution of the Fornax dwarf spheroidal and its globular clusters

ABSTRACT The dark matter content of the Fornax dwarf spheroidal galaxy inferred from its kinematics is substantially lower than expected from LCDM cosmological simulations. We use N-body simulations to examine whether this may be the result of Galactic tides. We find that, despite improved proper motions from the Gaia mission, the pericentric distance of Fornax remains poorly constrained, mainly because its largest velocity component is roughly antiparallel to the solar motion. Translating Fornax’s proper motion into a Galactocentric velocity is, thus, sensitively dependent on Fornax’s assumed distance: the observed distance uncertainty, $\pm 8\,{{\rm per\,cent}}$, implies pericentric distances that vary between rperi ∼ 50 and ∼150 kpc. Our simulations show that for rperi in the lower range of that estimate, an LCDM subhalo with maximum circular velocity Vmax = 40 km s−1 (or virial mass $M_{200}\approx 10^{10}\, \rm M_\odot$, as expected from LCDM) would be tidally stripped to Vmax ∼ 23 km s−1 over 10 Gyr. This would reduce the dark mass within the Fornax stellar half-mass radius to about half its initial value, bringing it into agreement with observations. Tidal stripping affects mainly Fornax’s dark matter halo; its stellar component is affected little, losing less than $5\,{{\rm per\,cent}}$ of its initial mass in the process. We also explore the effect of Galactic tides on the dynamical friction decay times of Fornax’s population of globular clusters (GCs) and find little evidence for substantial changes, compared with models run in isolation. A population of GCs with initial orbital radii between 1 and 2 kpc is consistent with the present-day spatial distribution of Fornax GCs, despite assuming a cuspy halo. Neither the dark matter content nor the spatial distribution of GCs of Fornax seems inconsistent with a simple model where Fornax inhabits a tidally stripped cuspy cold dark matter halo.

An accurate comprehensive approach to substructure – II. Stripped subhaloes

ABSTRACT In Salvador-Solé, Manrique & Botella (Paper I), we used the ConflUent System of Peak trajectories (CUSP) formalism to derive from first principles and no single free parameter the accurate abundance and radial distribution of both diffuse dark matter (dDM) and subhaloes accreted on to haloes and their progenitors at all previous times. Here we use those results as initial conditions for the monitoring of the evolution of subhaloes and dDM within the host haloes. Specifically, neglecting dynamical friction, we accurately calculate the effects of repetitive tidal stripping and heating on subhaloes as they orbit inside the host halo and infer the amount of dDM and subsubhaloes they release into the intrahalo medium. We then calculate the expected abundance and radial distribution of stripped subhaloes and dDM. This derivation clarifies the role of halo concentration in substructure and unravels the origin of some key features found in simulations including the dependence of substructure on halo mass. In addition, it unveils the specific effects of dynamical friction on substructure. The results derived here are for purely accreting haloes. In Salvador-Solé et al. (Paper III), we complete the study by addressing the case of low-mass subhaloes, unaffected by dynamical friction, in ordinary haloes having suffered major mergers.

A Disk and No Signatures of Tidal Distortion in the Galaxy “Lacking” Dark Matter NGC 1052-DF2

Abstract Using ultra-deep imaging (μ g = 30.4 mag arcsec−2; 3σ, 10″ × 10″), we probed the surroundings of the first galaxy “lacking” dark matter (DM) KKS2000[04] (NGC 1052–DF2). Signs of tidal stripping in this galaxy would explain its claimed low content of DM. However, we find no evidence of tidal tails. In fact, the galaxy remains undisturbed down to a radial distance of 80″. This radial distance triples previous spatial explorations of the stellar distribution of this galaxy. In addition, the distribution of its globular clusters (GCs) is not extended in relation to the bulk of the galaxy (the radius containing half of the GCs is 21″). We also found that the surface brightness radial profiles of this galaxy in the g and r bands decline exponentially from 35″ to 80″. Together with a constant ellipticity and position angle in the outer parts of the galaxy, this strongly suggests the presence of a low-inclination disk. This is consistent with the evidence of rotation found for this object. This finding implies that the dynamical mass of this galaxy is a factor of 2 higher than previously reported, which brings the DM content of this galaxy in line with galaxies of similar stellar mass.

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

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

Absence of obvious tidal tails around the globular cluster NGC 6397

ABSTRACT In this work, we use N-body simulations performed on GPU to trace the past 10 Gyr dynamical history of a globular cluster (GC) similar to NGC 6397 in the tidal field of a Milky Way-like galaxy and we compare our simulated GCs with data from the third Gaia early data release. Our simulations predict, in contrast to what is deduced from the data, that such a cluster should present strong and extended tidal tails by more than 6 Gyr ago (right after the first third of its life), exceeding 1 kpc of length, and should be roughly disrupted by current time. We analysed each of our initial conditions, such as initial mass and density parameters, as well as the dark matter shape, and we argue that the most likely reason for such discrepancy between the data and our simulations is related to the fact that we consider a purely baryonic cluster in the beginning of each model we test. We discuss that if our globular cluster was initially embedded in a dark matter minihalo, the latter could act as a protecting envelope, which prevents the tidal stripping of the luminous matter, while being itself gradually disrupted and removed in the course of the cluster evolution. This could explain why an insignificant amount of dark matter is required to describe the velocity dispersion in NGC 6397, up to at least a few half-mass radii.

Photometric and Kinematic Study of the Open Clusters SAI 44 and SAI 45

Abstract We carry out a detailed photometric and kinematic study of the poorly studied sparse open clusters SAI 44 and SAI 45 using ground-based BVR c I c data supplemented by archival data from Gaia eDR3 and Pan-STARRS. The stellar memberships are determined using a statistical method based on Gaia eDR3 kinematic data, and we found 204 members in SAI 44 while only 74 members are identified in SAI 45. The average distances to SAI 44 and SAI 45 are calculated to be 3670 ± 184 and 1668 ± 47 pc. The logarithmic age of the clusters are determined to be 8.82 ± 0.10 and 9.07 ± 0.10 yr for SAI 44 and SAI 45, respectively. The color–magnitude diagram of SAI 45 hosts an extended main-sequence turnoff (eMSTO). The apparent age spread is found to be similar to the apparent age spread predicted on the basis of the age spread and cluster age relation predicted by rotation models. This indicates that eMSTO is a stellar evolution rather than star formation phenomenon in SAI 45. We conclude that eMSTO in SAI 45 is mainly caused by the different rotation rates of stars as the SYCLIST synthetic population with different rotation rates was able to reproduce the observed eMSTO, and stars in the red part of the eMSTO were preferentially concentrated in the inner region, which again hints at different rotations being the reason for the extension in the upper MS. This finding supports the theory attributing the origin of eMSTO to the different rotations of eMSTO stars. The mass function slopes are obtained as −2.24 ± 0.66 and −2.58 ± 3.20 in the mass rages 2.426–0.990 M ⊙ and 2.167–1.202 M ⊙ for SAI 44 and SAI 45, respectively. SAI 44 exhibits the signature of mass segregation while we found weak evidence of mass segregation in SAI 45 possibly due to tidal stripping. The dynamical relaxation times of these clusters indicate that both clusters are in a dynamically relaxed state. Using the AD-diagram method, the apex coordinates are found to be ( 69 .° 79 ± 0 .° 11 , − 30 .° 82 ± 0 .° 15 ) for SAI 44 and (− 56 .° 22 ± 0 .° 13 , − 56 .° 62 ± 0 .° 13 ) for SAI 45. The average space velocity components of the clusters SAI 44 and SAI 45 are calculated in units of km s−1 as (−15.14 ± 3.90, −19.43 ± 4.41, −20.85 ± 4.57) and (28.13 ± 5.30, −9.78 ± 3.13, −19.59 ± 4.43), respectively.

A supra-massive population of stellar-mass black holes in the globular cluster Palomar 5.

Palomar 5 is one of the sparsest star clusters in the Galactic halo and is best-known for its spectacular tidal tails, spanning over 20 degrees across the sky. With N-body simulations we show that both distinguishing features can result from a stellar-mass black hole population, comprising ~ 20% of the present-day cluster mass. In this scenario, Palomar 5 formed with a 'normal' black hole mass fraction of a few per cent, but stars were lost at a higher rate than black holes, such that the black hole fraction gradually increased. This inflated the cluster, enhancing tidal stripping and tail formation. A gigayear from now, the cluster will dissolve as a 100% black hole cluster. Initially denser clusters end up with lower black hole fractions, smaller sizes, and no observable tails. Black hole-dominated, extended star clusters are therefore the likely progenitors of the recently discovered thin stellar streams in the Galactic halo.

Testing the tidal stripping scenario of ultracompact dwarf galaxy formation by using internal properties

ABSTRACT We use the hydrodynamical EAGLE simulation to test if ultracompact dwarf galaxies (UCDs) can form by tidal stripping by predicting the ages and metallicities of tidally stripped galaxy nuclei in massive galaxy clusters, and compare these results to compiled observations of age and metallicities of observed UCDs. We further calculate the colours of our sample of simulated stripped nuclei using single stellar population models and compare these colours to observations of UCDs in the Virgo Cluster. We find that the ages of observed UCDs are consistent with simulated stripped nuclei, with both groups of objects having a mean age >9 Gyr. Both stripped nuclei and UCDs follow a similar mass–metallicity relationship, and the metallicities of observed UCDs are consistent with those of simulated stripped nuclei for objects with M > 107 M⊙. The colours of observed UCDs are also consistent with our simulated stripped nuclei, for objects with M > 107 M⊙, with more massive objects being redder. We find that the colours of stripped nuclei exhibit a bimodal red and blue distribution that can be explained by the dependency of colour on age and metallicity, and by the mass–colour relation. We additionally find that our low-mass stripped nuclei sample is consistent with the colour of blue globular clusters. We conclude that the internal properties of simulated nuclei support the tidal stripping model of UCD formation.

Andromeda XXI – a dwarf galaxy in a low-density dark matter halo

ABSTRACT Andromeda XXI (And XXI) has been proposed as a dwarf spheroidal galaxy with a central dark matter density that is lower than expected in the standard $\Lambda$ cold dark matter ($\Lambda$CDM) cosmology. In this work, we present dynamical observations for 77 member stars in this system, more than doubling previous studies to determine whether this galaxy is truly a low-density outlier. We measure a systemic velocity of $v_r=-363.4\pm 1.0{\rm \, km\, s^{-1}}$ and a velocity dispersion of $\sigma _v=6.1^{+1.0}_{-0.9}{\rm \, km\, s^{-1}}$, consistent with previous work and within $1\sigma$ of predictions made using the modified Newtonian dynamics framework. We also measure the metallicity of our member stars from their spectra, finding a mean value of ${\rm [Fe/H]}=-1.7\pm 0.1$ dex. We model the dark matter density profile of And XXI using an improved version of gravsphere, finding a central density of $\rho _{\rm DM}({\rm 150 pc})=2.6_{-1.5}^{+2.4} \times 10^7 \, {\rm M_\odot \, kpc^{-3}}$ at 68 per cent confidence, and a density at two half-light radii of $\rho _{\rm DM}({\rm 1.75 kpc})=0.9_{-0.2}^{+0.3} \times 10^6 \, {\rm M_\odot \, kpc^{-3}}$ at 68 per cent confidence. These are both a factor of${\sim }3\!-\!5$ lower than the densities expected from abundance matching in $\Lambda$CDM. We show that this cannot be explained by ‘dark matter heating’ since And XXI had too little star formation to significantly lower its inner dark matter density, while dark matter heating only acts on the profile inside the half-light radius. However, And XXI’s low density can be accommodated within $\Lambda$CDM if it experienced extreme tidal stripping (losing ${\gt}95{{\ \rm per\ cent}}$ of its mass), or if it inhabits a low-concentration halo on a plunging orbit that experienced repeated tidal shocks.

Probing small-scale power spectra with pulsar timing arrays

Models of Dark Matter (DM) can leave unique imprints on the Universe’s small scale structure by boosting density perturbations on small scales. We study the capability of Pulsar Timing Arrays to search for, and constrain, subhalos from such models. The models of DM we consider are ordinary adiabatic perturbations in ΛCDM, QCD axion miniclusters, models with early matter domination, and vector DM produced during inflation. We show that ΛCDM, largely due to tidal stripping effects in the Milky Way, is out of reach for PTAs. Axion miniclusters may be within reach, although this depends crucially on whether the axion relic density is dominated by the misalignment or string contribution. Models where there is matter domination with a reheat temperature below 1 GeV may be observed with future PTAs. Lastly, vector DM produced during inflation can be detected if it is lighter than 10−16 GeV. We also make publicly available a Python Monte Carlo tool for generating the PTA time delay signal from any model of DM substructure.

The galaxy size–halo mass scaling relations and clustering properties of central and satellite galaxies

ABSTRACT In this work, we combine size and stellar mass measurements from the Sloan Digital Sky Server (SDSS) with the group finder algorithm of Rodriguez & Merchán in order to determine the stellar and halo mass–size relations of central and satellite galaxies separately. We show that, while central and satellite galaxies display similar stellar mass–size relations, their halo mass–size relations differ significantly. As expected, more massive haloes tend to host larger central galaxies. However, the size of satellite galaxies depends only slightly on halo virial mass. We show that these results are compatible with a remarkably simple model in which the size of central and satellite galaxies scales as the cubic root of their host halo mass, with the normalization for satellites being ∼30 per cent smaller than that for central galaxies, which can be attributed to tidal stripping. We further check that our measurements are in excellent agreement with predictions from the IllustrisTNG hydrodynamical simulation. In the second part of this paper, we analyse how the clustering properties of central and satellite galaxies depend on their size. We demonstrate that, independently of the stellar mass threshold adopted, smaller galaxies are more tightly clustered than larger galaxies when either the entire sample or only satellites are considered. The opposite trend is observed on large scales when the size split is performed for the central galaxies alone. Our results place significant constraints for halo–galaxy connection models that link galaxy size with the properties of their hosting haloes.

Soliton oscillations and revised constraints from Eridanus II of fuzzy dark matter

Fuzzy dark matter (FDM) has been a promising alternative to standard cold dark matter. The model consists of ultralight bosons with mass $m_b \sim 10^{-22}$ eV and features a quantum-pressure-supported solitonic core that oscillates. In this work, we show that the soliton density oscillations persist even after significant tidal stripping of the outer halo. We report two intrinsic yet distinct timescales associated, respectively, with the ground-state soliton wavefunction $\tau_{00}$ and the soliton density oscillations $\tau_\text{soliton}$, obeying $\tau_\text{soliton} /\tau_{00} \simeq 2.3$. The central star cluster (SC) in Eridanus II has a characteristic timescale $\tau_\text{soliton} / \tau_\text{SC} \sim 2$ to $3$ that deviates substantially from unity. As a result, we demonstrate, both analytically and numerically with three-dimensional self-consistent FDM simulations, that the gravitational heating of the SC owing to soliton density oscillations is negligible irrespective of $m_b$. We also show that the subhalo mass function to form Eridanus II does not place a strong constraint on $m_b$. These results are contrary to the previous findings by Marsh & Niemeyer (2019).

Linking globular cluster structural parameters and their evolution: multiple stellar populations

ABSTRACT Globular clusters (GCs) are known to host multiple stellar populations showing chemical anomalies in the content of light elements. The origin of such anomalies observed in Galactic GCs is still debated. Here we analyse data compiled from the Hubble Space Telescope, ground-based surveys, and Gaia Data Release 2 (DR2) and explore relationships between the structural properties of GCs and the fraction of second population (2P) stars. Given the correlations we find, we conclude that the main factor driving the formation/evolution of 2P stars is the cluster mass. The existing strong correlations between the 2P fraction and the rotational velocity and concentration parameter could derive from their correlation with the cluster mass. Furthermore, we observe that increasing cluster escape velocity corresponds to higher 2P fractions. Each of the correlations found is bimodal, with a different behaviour detected for low- and high-mass (or escape velocity) clusters. These correlations could be consistent with an initial formation of more centrally concentrated 2P stars in deeper cluster potentials, followed by a long-term tidal stripping of stars from clusters outskirts. The latter are dominated by the more extended distributed first population (1P) stars, and therefore stronger tidal stripping would preferentially deplete the 1P population, raising the cluster 2P fraction. This also suggests a tighter distribution of initial 2P fractions than observed today. In addition, higher escape velocities allow better retention of low-velocity material ejected from 1P stars, providing an alternative/additional origin for the observed differences and the distributions of 2P fractions amongst GCs.

Strongly lensed cluster substructures are not in tension with ΛCDM

ABSTRACT Strong gravitational lensing observations can test structure formation models by constraining the masses and concentrations of subhaloes in massive galaxy clusters. Recent work has concluded that cluster subhaloes are more abundant and/or concentrated than predicted by Λ cold dark matter (ΛCDM) simulations; this finding has been interpreted as arising from unidentified issues with simulations or an incorrect understanding of the nature of dark matter. We test these hypotheses by comparing observed subhalo masses and maximum circular velocities vmax to predictions from the high-resolution Hydrangea galaxy cluster simulation suite, which is based on the successful EAGLE galaxy formation model. Above ${\sim}10^{11}\, \mathrm{M}_\odot$, the simulated subhalo mass distribution and mass–vmax relation agrees well with observations, due to the presence of baryons during tidal stripping. Similar agreement is found for the lower resolution IllustrisTNG300 simulation. In combination, our results suggest that the abundance and concentration of cluster substructures are not in tension with ΛCDM, but may provide useful constraints for the refinement of baryon physics models in simulations.

Effective N-body models of composite collisionless stellar systems

ABSTRACT Gas-poor galaxies can be modelled as composite collisionless stellar systems, with a dark matter halo and one or more stellar components, representing different stellar populations. The dynamical evolution of such composite systems is often studied with numerical N-body simulations, whose initial conditions typically require realizations with particles of stationary galaxy models. We present a novel method to conceive these N-body realizations, which allows one to exploit at best a collisionless N-body simulation that follows their evolution. The method is based on the use of an effective N-body model of a composite system, which is in fact realized as a one-component system of particles that is interpreted a posteriori as a multicomponent system, by assigning in post-processing fractions of each particle’s mass to different components. Examples of astrophysical applications are N-body simulations that aim to reproduce the observed properties of interacting galaxies, satellite galaxies, and stellar streams. As a case study we apply our method to an N-body simulation of tidal stripping of a two-component (dark matter and stars) satellite dwarf galaxy orbiting in the gravitational potential of the Milky Way.