Satellites Of Hosts Research Articles

The dual role of outflows in quenching satellites of low-mass hosts: NGC 3109

ABSTRACT While dwarf galaxies observed in the field are overwhelmingly star forming, dwarf galaxies in environments as dense or denser than the Milky Way are overwhelmingly quenched. In this paper, we explore quenching in the lower density environment of the Small-Magellanic-Cloud-mass galaxy NGC 3109 (M$_* \sim 10^8 \, \text{M}_\odot$), which hosts two known dwarf satellite galaxies (Antlia and Antlia B), both of which are ${\rm H}\, \rm{\small I}$ deficient compared to similar galaxies in the field and have recently stopped forming stars. Using a new semi-analytic model in concert with the measured star formation histories and gas masses of the two dwarf satellite galaxies, we show that they could not have been quenched solely by direct ram pressure stripping of their interstellar media, as is common in denser environments. Instead, we find that separation of the satellites from pristine gas inflows, coupled with stellar-feedback-driven outflows from the satellites (jointly referred to as the starvation quenching model), can quench the satellites on time-scales consistent with their likely infall times into NGC 3109’s halo. It is currently believed that starvation is caused by ‘weak’ ram pressure that prevents low-density, weakly bound gas from being accreted on to the dwarf satellite, but cannot directly remove the denser interstellar medium. This suggests that star-formation-driven outflows serve two purposes in quenching satellites in low-mass environments: outflows from the host form a low-density circumgalactic medium that cannot directly strip the interstellar media from its satellites, but is sufficient to remove loosely bound gaseous outflows from the dwarf satellites driven by their own star formation.

Lopsided Satellite Distributions around Isolated Host Galaxies in a ΛCDM Universe

A recent observational study found that the projected spatial distributions of the satellites of bright, isolated host galaxies tend to be lopsided with respect to the locations of the hosts. Here, we examine the spatial distributions of the satellites of a large number of bright, isolated host galaxies that were obtained from mock redshift surveys of a Λ-cold dark matter (ΛCDM) simulation. Host galaxies and their satellites were identified using selection criteria that are identical to those used in the observational study, allowing for a direct comparison of the results for the simulated and observed systems. To characterize the spatial distribution of the satellites, we adopt two statistics: (1) the pairwise clustering of the satellites and (2) the mean resultant length. In agreement with the observational study, we find a strong tendency for satellites in the simulation to be located on the same side of their host, and the signal is most pronounced for the satellites of blue hosts. These lopsided satellite distributions are not solely attributable to incompleteness of the observed satellite catalog or the presence of objects that have been falsely identified as satellites. In addition, satellites that joined their hosts’ halos in the distant past (≳8 Gyr) show a pronounced lopsidedness in their spatial distributions and, therefore, the lopsidedness is not solely attributable to the late-time accretion of satellites.

The effects of LMC-mass environments on their dwarf satellite galaxies in the FIRE simulations

ABSTRACTCharacterizing the predicted environments of dwarf galaxies like the Large Magellanic Cloud (LMC) is becoming increasingly important as next-generation surveys push sensitivity limits into this low-mass regime at cosmological distances. We study the environmental effects of LMC-mass haloes (M200m ∼ 1011 M⊙) on their populations of satellites (M⋆ ≥ 104 M⊙) using a suite of zoom-in simulations from the Feedback In Realistic Environments (FIRE) project. Our simulations predict significant hot coronas with T ∼ 105 K and Mgas ∼ 109.5 M⊙. We identify signatures of environmental quenching in dwarf satellite galaxies, particularly for satellites with intermediate mass (M⋆ = 106–107 M⊙). The gas content of such objects indicates ram pressure as the likely quenching mechanism, sometimes aided by star formation feedback. Satellites of LMC-mass hosts replicate the stellar mass dependence of the quiescent fraction found in satellites of Milky Way-mass hosts (i.e. that the quiescent fraction increases as stellar mass decreases). Satellites of LMC-mass hosts have a wider variety of quenching times when compared to the strongly bimodal distribution of quenching times of nearby centrals. Finally, we identify significant tidal stellar structures around four of our six LMC analogues, suggesting that stellar streams may be common. These tidal features originated from satellites on close orbits, extend to ∼80 kpc from the central galaxy, and contain ∼106–107 M⊙ of stars.

The luminosity functions and redshift evolution of satellites of low-mass galaxies in the COSMOS survey

ABSTRACT The satellite populations of the Milky Way, and Milky Way mass galaxies in the local Universe, have been extensively studied to constrain dark matter and galaxy evolution physics. Recently, there has been a shift to studying satellites of hosts with stellar masses between that of the Large Magellanic Cloud and the Milky Way, since they can provide further insight on hierarchical structure formation, environmental effects on satellites, and the nature of dark matter. Most work is focused on the Local Volume, and little is still known about low-mass host galaxies at higher redshift. To improve our understanding of the evolution of satellite populations of low-mass hosts, we study satellite galaxy populations as a function of host stellar mass 9.5 < log (M*/M⊙) < 10.5 and redshifts 0.1 < $z$ < 0.8 in the COSMOS survey, making this the first study of satellite systems of low-mass hosts across half the age of the universe. We find that the satellite populations of low-mass host galaxies, which we measure down to satellite masses equivalent to the Fornax dwarf spheroidal satellite of the Milky Way, remain mostly unchanged through time. We observe a weak dependence between host stellar mass and number of satellites per host, which suggests that the stellar masses of the hosts are in the power-law regime of the stellar mass to halo mass relation (M*–Mhalo) for low-mass galaxies. Finally, we test the constraining power of our measured cumulative luminosity function to calculate the low-mass end slope of the M*–Mhalo relation. These new satellite luminosity function measurements are consistent with Lamda cold dark matter predictions.

Lopsided Satellite Distributions around Isolated Host Galaxies

Abstract We investigate the spatial distribution of the satellites of bright, isolated host galaxies. In agreement with previous studies, we find that, on average, the satellites of red hosts are found preferentially close to their hosts’ major axes, while the satellites of blue hosts are distributed isotropically. We compute the pairwise clustering of the satellites and find a strong tendency for pairs of satellites to be located on the same side of their host, resulting in lopsided spatial distributions. The signal is most pronounced for the satellites of blue hosts, where the number of pairs on the same side of their host exceeds the number of pairs on opposite sides of their host by a factor of 1.8 ± 0.1. For the satellites of red hosts, the number of pairs on the same side of their host exceeds the number of pairs on opposite sides of their host by a factor of 1.08 ± 0.03. Satellites that are far from their hosts (r p ≳ 300 kpc) show a strong preference for being located on the same side of their hosts; satellites that are near to their hosts (r p ≲ 100 kpc) show a weak preference for being located on opposite sides of their hosts. While lopsided distributions have been found previously for the satellites of bright pairs of galaxies, ours is the first study to find lopsided distributions for the satellites of isolated bright galaxies.

Lopsided Satellite Distributions around Isolated Host Galaxies

Abstract We summarize preliminary results from a new analysis of the spatial distributions of the satellites of isolated host galaxies. We identify 789 host-satellite systems in the NASA-Sloan Atlas, each with 5 or more satellites. Consistent with previous studies, we find that, on average, the satellites of red hosts are located preferentially close to their hosts’ major axes, while the satellites of blue hosts are distributed isotropically. The pairwise clustering of the satellites reveals a strong tendency for pairs of satellites to be located on the same side of their host, resulting in lopsided satellite distributions. The signal is most pronounced for the satellites of blue hosts, where we find ∼50% more satellite pairs on the same side of their host than on opposite sides. For red hosts, we find ∼6% more satellite pairs on the same side of their host than on opposite sides.

Star formation histories of dwarf galaxies in the FIRE simulations: dependence on mass and Local Group environment

ABSTRACT We study star formation histories (SFHs) of 500 dwarf galaxies (stellar mass $M_\ast =10^5\!-\!10^9\, \rm {M}_\odot$) from FIRE-2 cosmological zoom-in simulations. We compare dwarfs around individual Milky Way (MW)-mass galaxies, dwarfs in Local Group (LG)-like environments, and true field (i.e. isolated) dwarf galaxies. We reproduce observed trends wherein higher mass dwarfs quench later (if at all), regardless of environment. We also identify differences between the environments, both in terms of ‘satellite versus central’ and ‘LG versus individual MW versus isolated dwarf central.’ Around the individual MW-mass hosts, we recover the result expected from environmental quenching: central galaxies in the ‘near field’ have more extended SFHs than their satellite counterparts, with the former more closely resemble isolated (true field) dwarfs (though near-field centrals are still somewhat earlier forming). However, this difference is muted in the LG-like environments, where both near-field centrals and satellites have similar SFHs, which resemble satellites of single MW-mass hosts. This distinction is strongest for M* = 106–$10^7\, \rm {M}_\odot$ but exists at other masses. Our results suggest that the paired halo nature of the LG may regulate star formation in dwarf galaxies even beyond the virial radii of the MW and Andromeda. Caution is needed when comparing zoom-in simulations targeting isolated dwarf galaxies against observed dwarf galaxies in the LG.

Investigating the Stellar Mass Growth Histories of Satellite Galaxies as a Function of Infall Time Using Phase-space

Abstract We compile a large sample of nearby galaxies that are satellites of hosts using a well-known Sloan Digital Sky Survey (SDSS) group catalog. From this sample, we create an “ancient infallers” and “recent infallers” subsample, based on the mean infall time predicted from cosmological simulations for galaxies with their location in phase-space. We compare the stellar mass growth histories of the galaxies in these two subsamples, as determined from multiwavelength spectral energy distribution fitting that uses a comprehensive library of star formation history shapes derived from cosmological simulations. By simultaneously controlling for satellite stellar mass and host halo mass, we can clearly see the impact of time spent in their hosts. As we might predict, the ancient infaller population shows clear signs of earlier quenching, especially for lower mass satellites in more massive hosts. More importantly, we find that the effects are not limited to massive hosts. We find that hosts that might be considered low-mass groups (halo masses ∼1013 M ⊙) can significantly alter their satellites, even for massive satellites (stellar masses ∼1010 M ⊙). Intriguingly, we see changes in the mass growth history of the satellites of clusters as early as 8 or 9 Gyr ago, when they had not yet entered the virial radius of their current host. We propose that this could be the result of galaxies being preprocessed in low-mass substructures in the protocluster outskirts, prior to infall.

Satellite Galaxies in the Illustris-1 Simulation: Poor Tracers of the Mass Distribution

Abstract Number density profiles are computed for the satellites of relatively isolated host galaxies in the Illustris-1 simulation. The mean total mass density of the hosts is well fitted by a Navarro–Frenk–White (NFW) profile. The number density profile for the complete satellite sample is inconsistent with NFW, and on scales ≲0.5 r 200, the satellites do not trace the hosts’ mass. This differs substantially from previous results from semianalytic galaxy formation models. The shape of the satellite number density profile depends on the luminosities of the hosts and the satellites, and on the host virial mass. The number density profile for the faintest satellites is well fitted by an NFW profile, but the concentration is much less than the mean host mass density. The number density profile for the brightest satellites exhibits a steep increase in slope for host-satellite distances ≲0.1 r 200, in qualitative agreement with recent observational studies that find a steep increase in the satellite number density at small host-satellite distances. On scales ≳0.1 r 200 the satellites of the faintest hosts trace the host mass reasonably well. On scales ≲0.4 r 200, the satellites of the brightest hosts do not trace the host mass, and the satellite number density increases steeply for host-satellite distances ≲0.1 r 200. The discrepancy between the satellite number density profile and the host mass density is most pronounced for the most massive systems, with the satellite number density falling far below that of the mass density on scales ≲0.5 r 200.

YZiCS: Preprocessing of Dark Halos in the Hydrodynamic Zoom-in Simulation of Clusters

Abstract To understand the galaxy population in clusters today, we should also consider the impact of previous environments prior to cluster infall, namely preprocessing. We use the Yonsei Zoom-in Cluster Simulation, a hydrodynamic high-resolution zoom-in simulation of 15 clusters, and focus on the tidal stripping suffered by the dark matter halos of cluster members due to preprocessing. We find that ∼48% of today’s cluster members were once satellites of other hosts. This is slightly higher than previous estimates, in part because we consider not just group-mass hosts but hosts of all masses. Thus, we find that the preprocessed fraction is poorly correlated with cluster mass and is instead related to each cluster’s recent mass growth rate. Hosts less massive than groups are significant contributors, providing more than one-third of the total preprocessed fraction. We find that halo mass loss is a clear function of the time spent in hosts. However, two factors can increase the mass-loss rate considerably: the mass ratio of a satellite to its host and the cosmological epoch when the satellite was hosted. The latter means we may have previously underestimated the role of high-redshift groups. From a sample of heavily tidally stripped members in clusters today, nearly three-quarters were previously in a host. Thus, visibly disturbed cluster members are more likely to have experienced preprocessing. Being hosted before cluster infall enables cluster members to experience tidal stripping for extended durations compared to direct cluster infall and at earlier epochs when hosts were more destructive.

The Spatial Distribution of Satellite Galaxies Selected from Redshift Space

Abstract We investigate the spatial distribution of satellite galaxies using a mock redshift survey of the first Millennium Run simulation. The satellites were identified using common redshift space criteria, therefore the sample includes a large percentage of interlopers. The satellite locations are well fitted by a combination of a Navarro, Frenk and White (NFW) density profile and a power law. At fixed stellar mass, the NFW scale parameter, r s , for the satellite distribution of red hosts exceeds r s for the satellite distribution of blue hosts. In both cases, the dependence of r s on host stellar mass is well fitted by a power law. For the satellites of red hosts, r s red ∝ ( M * / M ⊙ ) 0.71 ± 0.05 , while for the satellites of blue hosts r s blue ∝ ( M * / M ⊙ ) 0.48 ± 0.07 . For hosts with stellar masses M * ≳ 4 × 10 10 M ⊙ , the satellite distribution around blue hosts is more concentrated than is the satellite distribution around red hosts. The spatial distribution of the satellites of red hosts traces that of the hosts’ halos; however, the spatial distribution of the satellites of blue hosts is more concentrated than that of the hosts’ halos by a factor of ∼2. Our methodology is general, and applies to any analysis of satellites in a mock redshift survey. However, our conclusions necessarily depend upon the semi-analytic galaxy formation model that was adopted, and different galaxy formation models may yield different results.

The mass dependence of satellite quenching in Milky Way-like haloes

Using the Sloan Digital Sky Survey, we examine the quenching of satellite galaxies around isolated Milky Way-like hosts in the local Universe. We find that the efficiency of satellite quenching around isolated galaxies is low and roughly constant over two orders of magnitude in satellite stellar mass ($M_{*}$ = $10^{8.5}-10^{10.5} \, M_{\odot}$), with only $\sim~20\%$ of systems quenched as a result of environmental processes. While largely independent of satellite stellar mass, satellite quenching does exhibit clear dependence on the properties of the host. We show that satellites of passive hosts are substantially more likely to be quenched than those of star-forming hosts, and we present evidence that more massive halos quench their satellites more efficiently. These results extend trends seen previously in more massive host halos and for higher satellite masses. Taken together, it appears that galaxies with stellar masses larger than about $10^{8}~M_{\odot}$ are uniformly resistant to environmental quenching, with the relative harshness of the host environment likely serving as the primary driver of satellite quenching. At lower stellar masses ($< 10^{8}~M_{\odot}$), however, observations of the Local Group suggest that the vast majority of satellite galaxies are quenched, potentially pointing towards a characteristic satellite mass scale below which quenching efficiency increases dramatically.

A dichotomy in satellite quenching around L* galaxies

We examine the star formation properties of bright (~0.1 L*) satellites around isolated ~L* hosts in the local Universe using spectroscopically confirmed systems in the Sloan Digital Sky Survey DR7. Our selection method is carefully designed with the aid of N-body simulations to avoid groups and clusters. We find that satellites are significantly more likely to be quenched than a stellar mass-matched sample of isolated galaxies. Remarkably, this quenching occurs only for satellites of hosts that are themselves quenched: while star formation is unaffected in the satellites of star-forming hosts, satellites around quiescent hosts are more than twice as likely to be quenched than stellar-mass matched field samples. One implication of this is that whatever shuts down star formation in isolated, passive L* galaxies also plays at least an indirect role in quenching star formation in their bright satellites. The previously-reported tendency for "galactic conformity" in color/morphology may be a by-product of this host-specific quenching dichotomy. The S\'ersic indices of quenched satellites are statistically identical to those of field galaxies with the same specific star formation rates, suggesting that environmental and secular quenching give rise to the same morphological structure. By studying the distribution of pairwise velocities between the hosts and satellites, we find dynamical evidence that passive host galaxies reside in dark matter halos that are ~45% more massive than those of star-forming host galaxies of the same stellar mass. We emphasize that even around passive hosts, the mere fact that galaxies become satellites does not typically result in star formation quenching: we find that only ~30% of ~0.1 L* galaxies that fall in from the field are quenched around passive hosts, compared with ~0% around star forming hosts.

LUMINOUS SATELLITES. II. SPATIAL DISTRIBUTION, LUMINOSITY FUNCTION, AND COSMIC EVOLUTION

We infer the normalization and the radial and angular distributions of the number density of satellites of massive galaxies ($\log_{10}[M_{h}^*/M\odot]>10.5$) between redshifts 0.1 and 0.8 as a function of host stellar mass, redshift, morphology and satellite luminosity. Exploiting the depth and resolution of the COSMOS HST images, we detect satellites up to eight magnitudes fainter than the host galaxies and as close as 0.3 (1.4) arcseconds (kpc). Describing the number density profile of satellite galaxies to be a projected power law such that $P(R)\propto R^{\rpower}$, we find $\rpower=-1.1\pm 0.3$. We find no dependency of $\rpower$ on host stellar mass, redshift, morphology or satellite luminosity. Satellites of early-type hosts have angular distributions that are more flattened than the host light profile and are aligned with its major axis. No significant average alignment is detected for satellites of late-type hosts. The number of satellites within a fixed magnitude contrast from a host galaxy is dependent on its stellar mass, with more massive galaxies hosting significantly more satellites. Furthermore, high-mass late-type hosts have significantly fewer satellites than early-type galaxies of the same stellar mass, likely a result of environmental differences. No significant evolution in the number of satellites per host is detected. The cumulative luminosity function of satellites is qualitatively in good agreement with that predicted using subhalo abundance matching techniques. However, there are significant residual discrepancies in the absolute normalization, suggesting that properties other than the host galaxy luminosity or stellar mass determine the number of satellites.

The impact of environment on the dynamical structure of satellite systems

We examine the effects of environment on the dynamical structure of satellite systems based on the Millennium--II Simulation. Satellite halos are defined as sub--halos within the virial radius of a host halo. The satellite sample is restricted to those sub--halos which showed a maximum circular velocity above 30 km/s at the time of accretion. Host halo masses range from 10^11 to 10^14 Msol/h. We compute the satellites' average accretion redshift, z_acc, velocity dispersion, sigma, and velocity anisotropy parameter, beta, utilising stacked satellite samples of equal mass hosts at similar background densities. The main results are: (1) On average satellites within hosts in high density environments are accreted earlier (Delta z~ 0.1$) compared to their counterparts at low densities. For host masses above 5 times10^13 Msol/h this trend weakens and may reverse for higher host masses; (2) The velocity dispersion of satellites in low density environments follows that of the host, i.e. no velocity bias is observed for host halos at low densities independent of host mass. However, for low mass hosts in high density environments the velocity dispersion of the satellites can be up to ~30% larger than that of the host halo, i.e. the satellites are dynamically hotter than their host halos. (3) The anisotropy parameter depends on host mass and environment. Satellites of massive hosts show more radially biased velocity distributions. Moreover in low density environments satellites have more radially biased velocities (Delta beta > 0.1) compared to their counterparts in high density environments. We believe that our approach allows to predict a similar behaviour for observed satellite galaxy systems.

ANISOTROPIC LOCATIONS OF SATELLITE GALAXIES: CLUES TO THE ORIENTATIONS OF GALAXIES WITHIN THEIR DARK MATTER HALOS

We investigate the locations of the satellites of relatively isolated host galaxies in the Sloan Digital Sky Survey and the Millennium Run simulation. Provided we use two distinct prescriptions to embed luminous galaxies within the simulated dark matter halos (ellipticals share the shapes of their halos, while disks have angular momenta that are aligned with the net angular momenta of their halos), we find a fair agreement between observation and theory. Averaged over scales rp ⩽ 500 kpc, the satellites of red, high-mass hosts with low star formation rates are found preferentially near the major axes of their hosts. In contrast, the satellites of blue, low-mass hosts with low star formation rates show little to no anisotropy when averaged over the same scale. The difference between the locations of the satellites of red and blue hosts cannot be explained by the effects of interlopers in the data. Instead, it is caused primarily by marked differences in the dependence of the mean satellite location, 〈ϕ〉, on the projected distance at which the satellites are found. We also find that the locations of red, high-mass satellites with low star formation rates show considerably more anisotropy than do the locations of blue, low-mass satellites with high star formation rates. There are two contributors to this result. First, the blue satellites have only recently arrived within their hosts' halos, while the red satellites arrived in the far distant past. Second, the sample of blue satellites is heavily contaminated by interlopers, which suppresses the measured anisotropy compared to the intrinsic anisotropy.

Constraints on the angular distribution of satellite galaxies about spiral hosts

We present, using a novel technique, a study of the angular distribution of satellite galaxies around a sample of isolated, blue host galaxies selected from the sixth data release of the Sloan Digital Sky Survey. As a complement to previous studies we subdivide the sample of galaxies into bins of differing inclination and use the systematic differences that would exist between the different bins as the basis for our approach. We parameterize the cumulative distribution function of satellite galaxies and apply a maximum likelihood, Monte-Carlo technique to determine allowable distributions, which we show as an exclusion plot. We find that the allowed distributions of the satellites of spiral hosts are very nearly isotropic. We outline our formalism and our analysis and discuss how this technique may be refined for future studies and future surveys.

Angular distribution of satellite galaxies from the Sloan Digital Sky Survey Data Release 4

Abstract We explore the angular distribution of two samples of satellite galaxies orbiting isolated hosts extracted from the Sloan Digital Sky Survey Data Release 4. We find a clear alignment of the satellites along the major axis of their hosts when restricting the analysis to red-coloured hosts. The anisotropy is most pronounced for red satellites of red hosts. We find that the distribution of the satellites about blue, isolated hosts is consistent with isotropy. We show that under the assumption that the true, underlying distribution of satellites of blue hosts exhibits the same anisotropy as the satellites of red hosts, the sample of blue hosts is too small to measure this anisotropy at a statistically significant level. The anisotropy that we detect for satellites about red hosts is independent of the projected radius. In particular, it is evident at large projected distances from the hosts (300 &amp;lt; rp Ϭ 500 kpc).