Globular Cluster Specific Frequency Research Articles

Constraining the stellar populations of ultra-diffuse galaxies in the MATLAS survey using spectral energy distribution fitting

ABSTRACT We use spectral energy distribution fitting to place constraints on the stellar populations of 59 ultra-diffuse galaxies (UDGs) in the low-to-moderate density fields of the MATLAS survey. We use the routine prospector, coupled with archival data in the optical from the Dark Energy Camera Legacy Survey, and near- and mid-infrared imaging from the Wide-field Infrared Survey Explorer, to recover the stellar masses, ages, metallicities, and star formation time-scales of the UDGs. We find that a subsample of the UDGs lies within the scatter of the mass–metallicity relation (MZR) for local classical dwarfs. However, another subsample is more metal-poor, being consistent with the evolving MZR at high redshift. We investigate UDG positioning trends in the mass–metallicity plane as a function of surface brightness, effective radius, axis ratio, local volume density, mass-weighted age, star formation time-scale, globular cluster (GC) counts, and GC specific frequency. We find that our sample of UDGs can be separated into two main classes: Class A: comprised of UDGs with lower stellar masses, prolonged star formation histories (SFHs), more elongated, inhabiting less dense environments, hosting fewer GCs, younger, consistent with the classical dwarf MZR, and fainter. Class B: UDGs with higher stellar masses, rapid SFHs, rounder, inhabiting the densest of our probed environments, hosting on average the most numerous GC systems, older, consistent with the high-redshift MZR (i.e. consistent with early-quenching), and brighter. The combination of these properties suggests that UDGs of Class A are consistent with a ‘puffed-up dwarf’ formation scenario, while UDGs of Class B seem to be better explained by ‘failed galaxy’ scenarios.

The influence of globular cluster evolution on the specific frequency in dwarf galaxies

ABSTRACT Dwarf galaxies are known to exhibit an unusual richness in numbers of globular clusters (GCs), property quantified by the specific frequency (SN), which is high for dwarf and giant elliptical galaxies, but with a minimum for intermediate-mass galaxies. In this work we study the role that GC evolution has in setting this trend, for which we use N-body simulations to evolve GCs in dwarf galaxies and quantify their disruption efficiency. We selected five individual dwarf galaxies from a high-resolution cosmological simulation, which includes GC formation and follow-up of their paths inside the host galaxy. Then, the tidal history of each GC is coupled to nbody6++gpu to produce N-body models that account for both, the interaction of GCs with their galactic environment and their internal dynamics. This results in a GC mass-loss parametrization to estimate dissolution times and mass-loss rates after a Hubble time. GC evolution is sensitive to the particular orbital histories within each galaxy, but the overall result is that the amount of mass that GC systems lose scales with the mass (and density) of the host galaxy, i.e. the GC mass-loss efficiency is lowest in low-mass dwarfs. After a 12 Gyr evolution all simulated GC systems retain an important fraction of their initial mass (up to 25 per cent), in agreement with the high GC to field star ratios observed in some dwarfs, and supports the scenario in which GC disruption mechanisms play an important role in shaping the GC specific frequency in dwarf galaxies.

The globular cluster system of the nearest Seyfert II galaxy Circinus

Context. The globular cluster (GC) system of Circinus galaxy has not been probed previously partly because of the location of the galaxy at −3.8° Galactic latitude, which suffers severely from interstellar extinction, stellar crowding, and Galactic foreground contamination. However, the deep near-infrared (NIR) photometry by the VISTA Variables in the Via Láctea Extended Survey (VVVX) in combination with the precise astrometry of Gaia EDR3 allow us to map GCs in this region. Aims. Our long-term goal is to study and characterise the distributions of GCs and ultra-compact dwarfs in Circinus galaxy, which is the nearest Seyfert II galaxy. Here we conduct the first pilot search for GCs in this galaxy. Methods. We used NIR VVVX photometry in combination with Gaia EDR3 astrometric features, such as astrometric excess noise and the ratio of the sum of the blue photometer (BP) and red photometer (RP) to the broad G passband (BRexcess), to build the first homogeneous catalogue of GCs in Circinus galaxy. A robust combination of selection criteria allows us to effectively clean interlopers from our sample. Results We report the detection of ∼70 GC candidates in this galaxy at a 3σ confidence level. They show a bimodal colour distribution with the blue peak at (G − Ks)0 = 0.985±0.127 mag with a dispersion of 0.211±0.091 mag and the red peak at (G − Ks)0 = 1.625±0.177 mag with a dispersion of 0.482±0.114 mag. A GC specific frequency (S​N) of 1.3±0.2 was derived for the galaxy, and we estimated a total population of 120±40 GCs. Based on the projected radial distribution it appears that Circinus has a different distribution of GC candidates than MW and M 31. Conclusions. We demonstrate that Circinus galaxy hosts a sizeable number of cluster candidates. This result is the first leap towards understanding the evolution of old stellar clusters in this galaxy.

Modelling globular clusters in the TNG50 simulation: predictions from dwarfs to giant galaxies

ABSTRACT We present a post-processing catalogue of globular clusters (GCs) for the 39 most massive groups and clusters in the TNG50 simulation of the IlllustrisTNG project (virial masses $M_{200} =[5\times 10^{12} \rm {\!-\!} 2 \times 10^{14}$] M⊙). We tag GC particles to all galaxies with stellar mass M* ≥ 5 × 106 M⊙, and we calibrate their masses to reproduce the observed power-law relation between GC mass and halo mass for galaxies with M200 ≥ 1011 M⊙ (corresponding to M* ∼ 109 M⊙). Here, we explore whether an extrapolation of this MGC–M200 relation to lower mass dwarfs is consistent with current observations. We find a good agreement between our predicted number and specific frequency of GCs in dwarfs with $\rm {\it M}_*=[5 \times 10^6 \rm {\!-\!} 10^9]$ M⊙ and observations. Moreover, we predict a steep decline in the GC occupation fraction for dwarfs with M* < 109 M⊙ that agrees well with current observational constraints. This declining occupation fraction is due to a combination of tidal stripping in all dwarfs plus a stochastic sampling of the GC mass function for dwarfs with M* < 107.5 M⊙. Our simulations also reproduce available constraints on the abundance of intracluster GCs in Virgo and Centaurus A. These successes provide support to the hypothesis that the MGC–M200 relation holds, albeit with more scatter, all the way down to the regime of classical dwarf spheroidals in these environments. Our GC catalogues are publicly available as part of the IllustrisTNG data release.

The Ancient Globular Clusters of NGC 1291

We present a new catalog of 81 ancient globular clusters (GCs) in the early-type spiral (SB0/a) galaxy NGC 1291. Candidates have been selected from B, V, and I band images taken with the Hubble Space Telescope, which also reveal 17 younger (τ ≲ few × 100 Myr) clusters. The luminosity function shows a peaked shape similar to that found for GC systems in other spiral and elliptical galaxies. The ancient clusters have a bimodal color distribution, with approximately 65% (35%) of the population having blue (red) colors. The red, presumably metal-rich, GCs are more centrally concentrated, as expected for a bulge population; while the blue, presumably metal-poor, GCs are more broadly distributed, consistent with expectations of a halo population. The specific frequency of GCs in NGC 1291 is higher than found previously in most spiral galaxies. However, if we consider just the blue subpopulation, we find S N,blue = 0.50 ± 0.06, quite similar to that found for other spirals. This result supports the hypothesis of a universal population of halo GCs in spirals. The fraction of red GCs in NGC 1291, when compared with those found in other galaxies, suggests that these correlate with host galaxy type rather than with host galaxy luminosity.

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.

The emergence of dark matter-deficient ultra-diffuse galaxies driven by scatter in the stellar mass–halo mass relation and feedback from globular clusters

ABSTRACT In addition to their low stellar densities, ultra-diffuse galaxies (UDGs) have a broad variety of dynamical mass-to-light ratios, ranging from dark matter (DM) dominated systems to objects nearly devoid of DM. To investigate the origin of this diversity, we develop a simple, semi-empirical model that predicts the structural evolution of galaxies, driven by feedback from massive star clusters, as a function of their departure from the mean SMHM relation. The model predicts that a galaxy located ≳ 0.5 dex above the mean relation at Mhalo = 1010 M⊙ will host a factor of ∼10–100 larger globular cluster (GC) populations, and that feedback from these GCs drives a significant expansion of the stellar component and loss of DM compared to galaxies on the SMHM relation. This effect is stronger in haloes that collapse earlier and have enhanced star formation rates at $z\gtrsim 2$, which leads to increased gas pressures, stellar clustering, and mean cluster masses, and significantly enhances the energy loading of galactic winds and its impact on the DM and stellar orbits. The impact on galaxy size and DM content can be large enough to explain observed galaxies that contain nearly the universal baryon fraction, as well as NGC 1052-DF2 and DF4 and other isolated UDGs that contain almost no DM. The trend of increasing galaxy size with GC specific frequency observed in galaxy clusters also emerges naturally in the model. Our predictions can be tested with large and deep surveys of the stellar and GC populations in dwarfs and UDGs. Because stellar clustering drives the efficiency of galactic winds, it may be a dominant factor in the structural evolution of galaxies and should be included as an essential ingredient in galaxy formation models.

ON THE PROBLEM OF THE SPECIFIC FREQUENCY OF GLOBULAR CLUSTERS

In the article, on the basis of observational data the problems of the specific frequency of globular clusters are studied. Possible relationships between them and the absolute stellar magnitude of their host galaxy are considered, where the observational data published in the literature were presented. It should be noted that before us the relationship between the specific frequency and the absolute magnitude is shown as exponential functions. An empirical relationship between the specific frequency and the absolute value of the host galaxy were obtained and showed that the dependence of the specific frequency on the absolute magnitude is not linear, but has a quadratic function. It is also shown that the specific frequency determines the number of globular clusters in a given galaxy relative to our Galaxy. Also in the article, based on the results of studies of the specific frequency, some discussions are presented related to the origin and evolution of globular clusters. The results obtained show that the ratios of the specific frequency to the luminosity of the host galaxy are different. Variations in the specific frequency of elliptical galaxies are associated with variations in the mass-to-luminous flux ratio. This may be due to the fact that the number of globular clusters in spiral galaxies per unit of luminosity of the halo and not of the entire galaxy. Analysis of the observational data shows that the values of the specific frequency of spiral galaxies are 5–6 times less than that of giant elliptical ones. As a result of the results of studies of the specific frequency of the globular clusters, unsolved problems are listed and possible solutions are shown. It is noted that the problem posed will be solved even more accurately if it is considered by the types of galaxies

Search for globular clusters associated with the Milky Way dwarf galaxies using Gaia DR2

ABSTRACT We report the result of searching for globular clusters (GCs) around 55 Milky Way (MW) satellite dwarf galaxies within the distance of 450 kpc from the Galactic Centre except for the Large and Small Magellanic Clouds and the Sagittarius dwarf. For each dwarf, we analyse the stellar distribution of sources in Gaia DR2, selected by magnitude, proper motion, and source morphology. Using the kernel density estimation of stellar number counts, we identify 11 possible GC candidates. Cross-matched with existing imaging data, all 11 objects are known either GCs or galaxies and only Fornax GC 1–6 among them are associated with the targeted dwarf galaxy. Using simulated GCs, we calculate the GC detection limit $M_{\rm V}^{\rm lim}$ that spans the range from $M_{\rm V}^{\rm lim}\sim -7$ for distant dwarfs to $M_{\rm V}^{\rm lim}\sim 0$ for nearby systems. Assuming a Gaussian GC luminosity function, we compute that the completeness of the GC search is above 90 per cent for most dwarf galaxies. We construct the 90 per cent credible intervals/upper limits on the GC specific frequency SN of the MW dwarf galaxies: 12 < SN < 47 for Fornax, SN < 20 for the dwarfs with −12 < MV < −10, SN < 30 for the dwarfs with −10 < MV < −7, and SN < 90 for the dwarfs with MV > −7. Based on SN, we derive the probability of galaxies hosting GCs given their luminosity, finding that the probability of galaxies fainter than MV = −9 to host GCs is lower than 0.1.

The first detection of ultra-diffuse galaxies in the Hydra I cluster from the VEGAS survey

In this paper, we report the discovery of 27 low-surface brightness galaxies, of which 12 are candidates for ultra-diffuse galaxies (UDG) in the Hydra I cluster, based on deep observations taken as part of the VST Early-type Galaxy Survey (VEGAS). This first sample of UDG candidates in the Hydra I cluster represents an important step in our project that aims to enlarge the number of confirmed UDGs and, through study of statistically relevant samples, constrain the nature and formation of UDGs. This study presents the main properties of this class of galaxies in the Hydra I cluster. For all UDGs, we analysed the light and colour distribution, and we provide a census of the globular cluster (GC) systems around them. Given the limitations of a reliable GC selection based on two relatively close optical bands only, we find that half of the UDG candidates have a total GC population consistent with zero. Of the other half, two galaxies have a total population larger than zero at 2σ level. We estimate the stellar mass, the total number of GCs, and the GC specific frequency (SN). Most of the candidates span a range of stellar masses of 107 − 108 M⊙. Based on the GC population of these newly discovered UDGs, we conclude that most of these galaxies have a standard or low dark matter content, with a halo mass of ≤1010 M⊙.

X-Ray Binary Luminosity Function Scaling Relations in Elliptical Galaxies: Evidence for Globular Cluster Seeding of Low-mass X-Ray Binaries in Galactic Fields

We investigate X-ray binary (XRB) luminosity function (XLF) scaling relations for Chandra detected populations of low-mass XRBs (LMXBs) within the footprints of 24 early-type galaxies. Our sample includes Chandra and HST observed galaxies at D < 25 Mpc that have estimates of the globular cluster (GC) specific frequency (SN) reported in the literature. As such, we are able to directly classify X-ray-detected sources as being either coincident with unrelated background/foreground objects, GCs, or sources that are within the fields of the galaxy targets. We model the GC and field LMXB population XLFs for all galaxies separately, and then construct global models characterizing how the LMXB XLFs vary with galaxy stellar mass and SN. We find that our field LMXB XLF models require a component that scales with SN, and has a shape consistent with that found for the GC LMXB XLF. We take this to indicate that GCs are "seeding" the galactic field LMXB population, through the ejection of GC-LMXBs and/or the diffusion of the GCs in the galactic fields themselves. However, we also find that an important LMXB XLF component is required for all galaxies that scales with stellar mass, implying that a substantial population of LMXBs are formed "in situ," which dominates the LMXB population emission for galaxies with SN < 2. For the first time, we provide a framework quantifying how directly-associated GC LMXBs, GC-seeded LMXBs, and in-situ LMXBs contribute to LMXB XLFs in the broader early-type galaxy population.

Simulating the spatial distribution and kinematics of globular clusters within galaxy clusters in illustris

ABSTRACT We study the assembly of globular clusters (GCs) in 9 galaxy clusters using the cosmological simulation Illustris. GCs are tagged to individual galaxies at their infall time. The tidal removal of GCs from their galaxies and the distribution of the GCs within the cluster is later followed self-consistently by the simulation. The method relies on the simple assumption of a single power-law relation between halo mass (Mvir) and mass in GCs (MGC) as found in observations. We find that the GCs specific frequency SN as a function of V-band magnitude naturally reproduces the observed ‘U’-shape due to the combination of the power law MGC–Mvir relation and the non-linear stellar mass (M*)–halo mass relation from the simulation. Additional scatter in the SN values is traced back to galaxies with early infall times due to the evolution of the M*–Mvir relation with redshift. GCs that have been tidally removed from their galaxies form the present-day intracluster component, from which about $\sim \!60{{\ \rm per\ cent}}$ were brought in by galaxies that currently orbit within the cluster potential. The remaining ‘orphan’ GCs are contributed by satellite galaxies with a wide range of stellar masses that are fully tidally disrupted at z = 0. This intracluster component is a good dynamical tracer of the dark matter potential. As a consequence of the accreted nature of most intracluster GCs, their orbits are fairly radial with a predicted orbital anisotropy β ≥ 0.5. However, local tangential motions may appear as a consequence of localized substructure, providing a possible interpretation to the β &amp;lt; 0 values suggested in observations of M87.

X-Ray Binary Luminosity Function Scaling Relations for Local Galaxies Based on Subgalactic Modeling

We present new Chandra constraints on the X-ray luminosity functions (XLFs) of X-ray binary (XRB) populations, and their scaling relations, for a sample of 38 nearby galaxies (D = 3.4-29 Mpc). Our galaxy sample is drawn primarily from the Spitzer infrared nearby galaxy survey (SINGS), and contains a wealth of Chandra (5.8 Ms total) and multiwavelength data, allowing for star-formation rates (SFRs) and stellar masses (M*) to be measured on subgalactic scales. We divided the 2478 X-ray detected sources into 21 subsamples in bins of specific-SFR (sSFR = SFR/M*) and constructed XLFs. To model the XLF dependence on sSFR, we fit a global XLF model, containing contributions from high-mass XRBs (HMXBs), low-mass XRBs (LMXBs), and background sources from the cosmic X-ray background (CXB) that respectively scale with SFR, M*, and sky area. We find an HMXB XLF that is more complex in shape than previously reported and an LMXB XLF that likely varies with sSFR, potentially due to an age dependence. When applying our global model to XLF data for each individual galaxy, we discover a few galaxy XLFs that significantly deviate from our model beyond statistical scatter. Most notably, relatively low-metallicity galaxies have an excess of HMXBs above ~10^38 erg/s and elliptical galaxies that have relatively rich populations of globular clusters (GCs) show excesses of LMXBs compared to the global model. Additional modeling of how the XRB XLF depends on stellar age, metallicity, and GC specific frequency is required to sufficiently characterize the XLFs of galaxies.

On the primordial specific frequency of globular clusters in dwarf and giant elliptical galaxies

Globular clusters (GC) are important objects for tracing the early evolution of a galaxy. We study the relation between the properties of globular cluster systems - as quantified by the GC specific frequency (SN) - and the properties of their host galaxies. In order to understand the origin of the relation between the GC specific frequency (SN) and galaxy mass, we devise a theoretical model for the specific frequency (SN,th). GC erosion is considered to be an important aspect for shaping this relation, since observations show that galaxies with low densities have a higher SN, while high density galaxies have a small SN. We construct a model based on the hypothesis that star-formation is clustered and depends on the minimum embedded star cluster mass (Mecl,min), the slope of the power-law embedded cluster mass function (beta) and the relation between the star formation rate (SFR) and the maximum star cluster mass (Mecl,max). We find an agreement between the primordial value of the specific frequency (SNi) and our model for beta between 1.5 and 2.5 with Mecl,min <10^4 Msun.

The ACS Fornax Cluster Survey. III. Globular Cluster Specific Frequencies of Early-type Galaxies

Abstract The globular cluster (GC) specific frequency (S N ), defined as the number of GCs per unit galactic luminosity, represents the efficiency of GC formation (and survival) compared to field stars. Despite the naive expectation that star cluster formation should scale directly with star formation, this efficiency varies widely across galaxies. To explore this variation, we measure the z-band GC specific frequency ( ) for 43 early-type galaxies (ETGs) from the Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) Fornax Cluster Survey. Combined with the homogeneous measurements of in 100 ETGs from the HST/ACS Virgo Cluster Survey from Peng et al., we investigate the dependence of on mass and environment over a range of galaxy properties. We find that behaves similarly in the two galaxy clusters, despite the clusters’ order-of-magnitude difference in mass density. The is low in intermediate-mass ETGs (−20 &lt; M z  &lt; −23) and increases with galaxy luminosity. It is elevated at low masses, on average, but with a large scatter driven by galaxies in dense environments. The densest environments with the strongest tidal forces appear to strip the GC systems of low-mass galaxies. However, in low-mass galaxies that are not in strong tidal fields, denser environments correlate with enhanced GC formation efficiencies. Normalizing by inferred halo masses, the GC mass fraction, η = (3.36 ± 0.2) × 10−5, is constant for ETGs with stellar masses , in agreement with previous studies. The lack of correlation between the fraction of GCs and the nuclear light implies only a weak link between the infall of GCs and the formation of nuclei.

The Globular Cluster Systems of Ultra-diffuse Galaxies in the Coma Cluster

Abstract Ultra-diffuse galaxies (UDGs) are unusual galaxies with low luminosities, similar to classical dwarf galaxies, but with sizes up to ∼5 larger than expected for their mass. Some UDGs have large populations of globular clusters (GCs), something unexpected in galaxies with such low stellar density and mass. We have carried out a comprehensive study of GCs in both UDGs and classical dwarf galaxies at comparable stellar masses using Hubble Space Telescope (HST) observations of the Coma cluster. We present new imaging for 33 Dragonfly UDGs with the largest effective radii (&gt;2 kpc), and additionally include 15 UDGs and 54 classical dwarf galaxies from the HST/ACS Coma Treasury Survey and the literature. Out of a total of 48 UDGs, 27 have statistically significant GC systems, and 11 have candidate nuclear star clusters. The GC specific frequency (S N ) varies dramatically, with the mean S N being higher for UDGs than for classical dwarfs. At constant stellar mass, galaxies with larger sizes (or lower surface brightnesses) have higher S N , with the trend being stronger at higher stellar mass. At lower stellar masses, UDGs tend to have higher S N when closer to the center of the cluster, i.e., in denser environments. The fraction of UDGs with a nuclear star cluster also depends on environment, varying from ∼40% in the cluster core, where it is slightly lower than the nucleation fraction of classical dwarfs, to ≲20% in the outskirts. Collectively, we observe an unmistakable diversity in the abundance of GCs, and this may point to multiple formation routes.

Dissolved Massive Metal-rich Globular Clusters Can Cause the Range of UV Upturn Strengths Found among Early-type Galaxies

Abstract I discuss a scenario in which the ultraviolet (UV) upturn of giant early-type galaxies (ETGs) is primarily due to helium-rich stellar populations that formed in massive metal-rich globular clusters (GCs), which subsequently dissolved in the strong tidal field in the central regions of the massive host galaxy. These massive GCs are assumed to show UV upturns similar to those observed recently in M87, the central giant elliptical galaxy in the Virgo cluster of galaxies. Data taken from the literature reveal a strong correlation between the strength of the UV upturn and the specific frequency of metal-rich GCs in ETGs. Adopting a Schechter function parameterization of GC mass functions, simulations of long-term dynamical evolution of GC systems show that the observed correlation between UV upturn strength and GC specific frequency can be explained by variations in the characteristic truncation mass such that increases with ETG luminosity in a way that is consistent with observed GC luminosity functions in ETGs. These findings suggest that the nature of the UV upturn in ETGs and the variation of its strength among ETGs are causally related to that of helium-rich populations in massive GCs, rather than intrinsic properties of field stars in massive galactic spheroids. With this in mind, I predict that future studies will find that [N/Fe] decreases with increasing galactocentric radius in massive ETGs, and that such gradients have the largest amplitudes in ETGs with the strongest UV upturns.

Tracing the assembly history of NGC 1395 through its Globular Cluster System

We used deep Gemini-South/GMOS g'r'i'z' images to study the globular cluster (GC) system of the massive elliptical galaxy NGC 1395, located in the Eridanus supergroup. The photometric analysis of the GC candidates reveals a clear colour bimodality distribution, indicating the presence of "blue" and "red" GC subpopulations. While a negative radial colour gradient is detected in the projected spatial distribution of the red GCs, the blue GCs display a shallow colour gradient. The blue GCs also display a remarkable shallow and extended surface density profile, suggesting a significant accretion of low-mass satellites in the outer halo of the galaxy. In addition, the slope of the projected spatial distribution of the blue GCs in the outer regions of the galaxy, is similar to that of the X-ray halo emission. Integrating up to 165 kpc the profile of the projected spatial distribution of the GCs, we estimated a total GC population and specific frequency of 6000$\pm$1100 and $S_N$=7.4$\pm$1.4, respectively. Regarding NGC 1395 itself, the analysis of the deep Gemini/GMOS images shows a low surface brightness umbrella-like structure indicating, at least, one recent merger event. Through relations recently published in the literature, we obtained global parameters, such as $M_\mathrm{stellar}=9.32\times10^{11}$ M$\odot$ and $M_h=6.46\times10^{13}$ M$\odot$. Using public spectroscopic data, we derive stellar population parameters of the central region of the galaxy by the full spectral fitting technique. We have found that, this region, seems to be dominated for an old stellar population, in contrast to findings of young stellar populations from the literature.

Specific Frequencies and Luminosity Profiles of Cluster Galaxies and Intracluster Light in Abell 1689

Abstract We present magnitudes and profile fits for 180 galaxies in the central field of the massive lensing cluster Abell 1689 using very deep imaging with the Hubble Space Telescope Advanced Camera for Surveys in the F814W bandpass. Previous work revealed an exceptionally large number of globular clusters (GCs) in A1689 and mapped their number density distribution. We decompose this number density map into GCs associated with individual cluster galaxies and ICGCs (intracluster GCs) associated with the intracluster light (ICL). In all, we measure GC specific frequencies S N for 33 cluster members and the ICL. The relation between S N and galaxy magnitude is consistent with the trend observed in Virgo, although some intermediate-luminosity galaxies scatter to S N &gt; 10 . We estimate that the ICL makes up 11% of the starlight in this field, whereas the ICGCs account for ∼35% of the GCs, both consistent with predictions from simulations. Galaxies with higher S N values tend to be rounder, and there is a marginally significant trend of decreasing S N with increasing specific angular momenta  λ R . We also reevaluate the GC population in the A2744 Frontier Field, for which fewer than 1/10 as many GCs have been detected because of its larger distance. Finally, our core-Sérsic fit to the light profile of the A1689 brightest cluster galaxy implies a break radius of 3.8 kpc, among the largest known; we discuss implications of the sizable core and extensive GC population for the supermassive black hole in light of scaling relations.

ARE SOME MILKY WAY GLOBULAR CLUSTERS HOSTED BY UNDISCOVERED GALAXIES?

ABSTRACT The confirmation of a globular cluster (GC) in the recently discovered ultrafaint galaxy Eridanus II (Eri II) motivated us to examine the question posed in the title. After estimating the halo mass of Eri II using a published stellar mass—halo mass relation, the one GC in this galaxy supports extending the relationship between the number of GCs hosted by a galaxy and the galaxy’s total mass about two orders of magnitude in stellar mass below the previous limit. For this empirically determined specific frequency of between 0.06 and 0.39 GCs per 109 M ⊙ of total mass, the surviving Milky Way (MW) subhalos with masses smaller than 1010 M ⊙ could host as many as 5–31 GCs, broadly consistent with the actual population of outer halo MW GCs, although matching the radial distribution in detail remains a challenge. Using a subhalo mass function from published high-resolution numerical simulations and a Poissonian model for populating those halos with the aforementioned empirically constrained frequency, we find that about 90% of these GCs lie in lower-mass subhalos than that of Eri II. From what we know about the stellar mass–halo mass function, the subhalo mass function, and the mass-normalized GC specific frequency, we conclude that some of the MW’s outer halo GCs are likely to be hosted by undetected subhalos with extremely modest stellar populations.