Dwarf Galaxies in the MATLAS Survey: Hubble Space Telescope Observations of the Globular Cluster Systems of 74 Ultra Diffuse Galaxies
Francine R. Marleau, Pierre-Alain Duc, Melina Poulain, Oliver Mueller, Sungsoon Lim, Patrick R. Durrell, Rebecca Habas, Ruben Sanchez-Janssen, Sanjaya Paudel, Jeremy Fensch
备注：
20 pages, 17 figures, 2 tables, accepted for publication in A&A
Ultra diffuse galaxies, characterized by their low surface brightness and large physical size, constitute a subclass of dwarf galaxies that challenge our current understanding of galaxy formation and evolution. In this paper, we probe the properties of 74 UDGs, identified in the MATLAS survey, based on a comprehensive study of their globular cluster (GC) populations. We obtained high resolution HST imaging of these galaxies using the ACS F606W and F814W filters, allowing us to select GCs based on color and concentration index. After background subtraction and completeness correction, we calculate an overall total of 387 GCs. The number of GCs per galaxy ranges from 0 to 38, with the majority (64%) having low counts (0-2 GCs). On average, the more massive UDGs host a larger number of GCs. We find that our UDGs have specific frequencies (S_N) ranging from 0 to 91, with a small population (9%) with S_N > 30. The median S_N of our sample is similar to the one for the Perseus cluster UDGs, despite the fact that our UDGs are found in lower density environments. The S_N measurements for individual galaxies can extend beyond those found in Perseus, but remain below the values found for UDGs in the Virgo and Coma cluster. Based on a trending analysis of the S_N values with the host galaxy properties, we find trends with host galaxy size, roundness, color, and local density. For the UDGs with sufficiently high statistics, we study 2D density maps of the GC distributions, which show a variety of appearances: symmetric, asymmetric, off-center, and elongated. The UDGs with disturbed density maps also show disturbed stellar light morphologies. We further quantify the distribution by modeling it with a Sersic profile, finding R_{e,GC}/R_{e,gal} ~ 1.0, which indicates that the GCs follow the stellar light of the host galaxy.
The MATLAS deep imaging survey has uncovered a plethora of dwarf galaxies in the low density environment it has mapped. A fraction of them are unusually extended and have a low-surface brightness. Among these so-called ultra-diffuse galaxies, a few seem to host an excess of globular clusters. With the integral-field unit spectrograph MUSE we have observed one of these galaxies - MATLAS J15052031+0148447 (MATLAS-2019) - located towards the nearby group NGC 5846 and measured its systemic velocity,age, and metallicity, and that of its globular clusters candidates. For the stellar body of MATLAS-2…
Ultra-diffuse galaxies (UDGs) are very low-surface brightness galaxies with large effective radii. Spectroscopic measurements of a few UDGs have revealed a low dark matter content, based on the internal motion of stars or globular clusters (GCs). This is in contrast to the large number of GCs found for these systems, from which it would be expected to correspond to a large dark matter halo mass. Here we present HST+ACS observations for the UDG MATLAS-2019 in the NGC5846 group. Using the F606W and F814W filters, we trace the GC population two magnitudes below the peak of the GC luminosity funct…
The presence of HI gas in galaxies is inextricably linked to their morphology and evolution. This paper aims to understand the HI content of the already identified 2210 dwarfs located in the low-to-moderate density environments of the MATLAS deep imaging survey. We combine the HI observations from the ATLAS$^{3D}$ survey, with the extragalactic HI sources from the ALFALFA survey, to extract the HI line width, velocity and mass of the MATLAS dwarfs. From the 1773 dwarfs in our sample with available HI observations, 8% (145) have an HI line detection. The majority of the dwarfs show irregular mo…
We study the evolution of star clusters located in the outer regions of a galaxy undergoing a sudden mass loss through gas expulsion in the framework of Milgromian dynamics (MOND) by means of N-body simulations. We find that, to leave a bound star cluster, the star formation efficiency (SFE) of an embedded cluster dominated by deep MOND gravity can be reduced down to $2.5\%$. For a given SFE, the star clusters that survive in MOND can bind a larger fraction of mass compared to the Newtonian dynamics. Moreover, the more diffuse the embedded cluster is, the less substantial the size expansion of…
We recently published velocity measurements of luminous globular clusters in the galaxy NGC1052-DF2, concluding that it lies far off the canonical stellar mass - halo mass relation. Here we present a revised velocity for one of the globular clusters, GC-98, and a revised velocity dispersion measurement for the galaxy. We find that the intrinsic dispersion $σ=5.6^{+5.2}_{-3.8}$ km/s using Approximate Bayesian Computation, or $σ=7.8^{+5.2}_{-2.2}$ km/s using the likelihood. The expected dispersion from the stars alone is ~7 km/s. Responding to a request from the Editors of ApJ Letters and RNAAS,…
Diffuse interstellar bands (DIBs) are weak absorption features of interstellar origin present in the optical and infrared spectra of stars. Their use as a tool to trace the structure of the Galactic ISM is gaining relevance in the recent years. Here we present an experiment to test our ability to trace differential reddening on the plane of the sky by using the information relative to the DIB at $λ$6614 extracted from the spectra of cool stars. For that we made use of archive FLAMES data of the globular cluster M4, as well as WISE and Planck images for reference. We found a global positive tre…
We introduce a new method for detecting ultra-diffuse galaxies by searching for over-densities in intergalactic globular cluster populations. Our approach is based on an application of the log-Gaussian Cox process, which is a commonly used model in the spatial statistics literature but rarely used in astronomy. This method is applied to the globular cluster data obtained from the PIPER survey, a \textit{Hubble Space Telescope} imaging program targeting the Perseus cluster. We successfully detect all confirmed ultra-diffuse galaxies with known globular cluster populations in the survey. We also…
Distance determinations of extremely-low-surface-brightness galaxies are expensive in terms of spectroscopic time. Because of this, their distances are often inferred by associating such galaxies with larger structures such as groups or clusters, leading to a systematic bias by selecting objects in high density environments. Here we report the discovery of a red ultra-diffuse galaxy (S82-DG-1: $r_{\mathrm{eff}}$ = 1.6 kpc; $<μ_{g}>$ = 25.7 mag arcsec$^{-2}$; $g-i$ = 0.78 mag) located in a nearby cosmic void. We used multi-band luminosity functions of its globular clusters to obtain the distanc…
Recent advances in deep dedicated imaging surveys over the past decade have uncovered a surprisingly large number of extremely faint low surface brightness galaxies with large physical sizes called ultra diffuse galaxies (UDGs) in clusters and, more recently, in lower density environments. As part of the MATLAS survey, a deep imaging large program at the Canada-France-Hawaii Telescope (CFHT), our team has identified 2210 dwarf galaxies, 59 (~3%) of which qualify as UDGs. Averaging over the survey area, we find ~0.4 UDG per square degree. They are found in a range of low to moderate density env…
We present Hubble Space Telescope imaging of two ultra diffuse galaxies (UDGs) with measured stellar velocity dispersions in the Coma cluster. The galaxies, Dragonfly 44 and DFX1, have effective radii of 4.7 kpc and 3.5 kpc and velocity dispersions of $47^{+8}_{-6}$ km/s and $30^{+7}_{-7}$ km/s, respectively. Both galaxies are associated with a striking number of compact objects, tentatively identified as globular clusters: $N_{\rm gc}=74\pm 18$ for Dragonfly 44 and $N_{\rm gc}=62\pm 17$ for DFX1. The number of globular clusters is far higher than expected from the luminosities of the galaxies…
We present Hubble Space Telescope imaging of 14 gas-rich, low surface brightness galaxies in the field at distances of 25-36 Mpc, with mean effective radii and $g$-band central surface brightnesses of 1.9 kpc and 24.2 mag arcsec$^{-2}$. Nine meet the standard criteria to be considered ultra-diffuse galaxies (UDGs). An inspection of point-like sources brighter than the turnover magnitude of the globular cluster luminosity function and within twice the half-light radii of each galaxy reveals that, unlike those in denser environments, gas-rich, field UDGs host very few old globular clusters (GCs)…
MATLAS-42, A Globular Cluster-Rich Ultra-Diffuse Galaxy That Diverges from the "Failed Galaxy'' Formation Pathway
Swinburne University（斯威本科技大学）；Instituto de Astrofísica de Canarias（加那利群岛天体物理学研究所）；Universidad de La Laguna（拉古纳大学）；San José State University（圣何塞州立大学）；University of California Santa Cruz（加州大学圣克鲁兹分校）；Yale University（耶鲁大学）
Modelling and Subtracting Diffuse Cluster Light in JWST Images: A Relation between the Spatial Distribution of Globular Clusters, Dwarf Galaxies, and Intracluster Light in the Lensing Cluster SMACS 0723
We present an analysis of the radial dependence of the stellar mass function in the diffuse outer-halo globular cluster Palomar 14. Using archival HST/WFPC2 data of the cluster's central 39 pc (corresponding to ~0.85*r_h) we find that the mass function in the mass range of 0.55 to 0.85 solar masses is well approximated by a power-law at all radii. The mass function steepens with increasing radius, from a shallow power-law slope of 0.66+/-0.32 in the cluster's centre to a slope of 1.61+/-0.33 beyond the core radius, showing that the cluster is mass-segregated. This is seemingly in conflict with…
It is clear that within the class of ultra-diffuse galaxies (UDGs) there is an extreme range in the richness of their associated globular cluster (GC) systems. Here, we report the structural properties of five UDGs in the Perseus cluster based on deep Subaru / Hyper Suprime-Cam imaging. Three appear GC-poor and two appear GC-rich. One of our sample, PUDG\_R24, appears to be undergoing quenching and is expected to fade into the UDG regime within the next $\sim0.5$ Gyr. We target this sample with Keck Cosmic Web Imager (KCWI) spectroscopy to investigate differences in their dark matter halos, as…
We increase the sample of ultra diffuse galaxies (UDGs) in lower density environments with characterized globular cluster (GC) populations using new Hubble Space Telescope observations of nine UDGs in group environments. While the bulk of our UDGs have GC abundances consistent with normal dwarf galaxies, two of these UDGs have excess GC populations. These two UDGs both have GC luminosity functions consistent with higher surface brightness galaxies and cluster UDGs. We then combine our nine objects with previous studies to create a catalog of UDGs with analyzed GC populations that spans a uniqu…
We investigate the isolated, quiescent ultra-diffuse galaxy (UDG) DGSAT I and its globular cluster (GC) system using two orbits of Hubble Space Telescope Advanced Camera for Surveys imaging in the F606W and F814W filters. This is the first study of GCs around a UDG in a low-density environment. DGSAT I was previously found to host an irregular blue low surface brightness clump, that we confirm as very likely belonging to the galaxy rather than being a chance projection, and represents a recent episode of star formation (${\sim}500~\mathrm{Myr}$) that challenges some UDG formation scenarios. We…
We present an analysis of Hubble Space Telescope observations of globular clusters (GCs) in six ultra-diffuse galaxies (UDGs) in the Coma cluster, a sample that represents UDGs with large effective radii ($R_{\rm e}$), and use the results to evaluate competing formation models. We eliminate two significant sources of systematic uncertainty in the determination of the number of GCs, $N_{\rm GC}$ by using sufficiently deep observations that (i) reach the turnover of the GC luminosity function and (ii) provide a sufficient number of GCs with which to measure the GC number radial distribution. We …
Ultra-diffuse galaxies that contain a large sample of globular clusters (GCs) offer an opportunity to test the predictions of galactic dynamics theory. NGC5846-UDG1 is an excellent example, with a high-quality sample of dozens of GC candidates. We show that the observed distribution of GCs in NGC5846-UDG1 is suggestive of mass segregation induced by gravitational dynamical friction. We present simple analytic calculations, backed by a series of numerical simulations, that naturally explain the observed present-day pattern of GC masses and radial positions. Subject to some assumptions on the GC…
Observations of nearby galaxy clusters at low surface brightness have identified galaxies with low luminosities, but sizes as large as L* galaxies, leading them to be dubbed "ultra-diffuse galaxies" (UDGs). The survival of UDGs in dense environments like the Coma cluster suggests that UDGs could reside in much more massive dark halos. We report the detection of a substantial population of globular clusters (GCs) around a Coma UDG, Dragonfly 17 (DF17). We find that DF17 has a high GC specific frequency of S_N=26+/-13. The GC system is extended, with an effective radius of 12"+/-2", or 5.6+/-0.9…
The MATLAS project explores the surroundings of a complete sample of nearby massive early-type galaxies with multi-colour deep optical images obtained at the Canada-France Hawaii Telescope. The observing and data reduction techniques ensured the detection of extended low-surface-brightness (LSB) structures, while the high image quality allowed us to identify associated compact objects such as star clusters. A number of scientific topics are addressed with this data-set that are briefly presented in this review: the study of foreground Galactic cirrus at high spatial resolution, telling us abou…
Ultra-diffuse galaxies (UDGs) are unusual galaxies with low luminosities, similar to classical dwarf galaxies, but sizes up to $\sim\!5$ 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 HST observations of the Coma cluster. We present new imaging for 33 Dragonfly UDGs with the largest effective radii ($>2$ kpc), and additionally include 15 UDGs and 5…
We present Keck/DEIMOS spectroscopy of globular clusters (GCs) around the ultra-diffuse galaxies (UDGs) VLSB-B, VLSB-D, and VCC615 located in the central regions of the Virgo cluster. We spectroscopically identify 4, 12, and 7 GC satellites of these UDGs, respectively. We find that the three UDGs have systemic velocities ($V_{sys}$) consistent with being in the Virgo cluster, and that they span a wide range of velocity dispersions, from $\sim 16$ to $\sim 47$ km/s, and high dynamical mass-to-light ratios within the radius that contains half the number of GCs ($ 407^{+916}_{-407}$, $21^{+15}_{-…
We present an analysis of archival {\it HST/ACS} imaging in the F475W ($g_{475}$), F606W ($V_{606}$) and F814W ($I_{814}$) bands of the globular cluster (GC) system of a large (3.4 kpc effective radius) ultra-diffuse galaxy (DF17) believed located in the Coma Cluster of galaxies. We detect 11 GCs down to the 5$σ$ completeness limit of the imaging ($I_{814}=$27 mag). Correcting for background and our detection limits yields a total population of GCs in this galaxy of $27\pm5$ and a $V$-band specific frequency, $S_N=28\pm5$. Based on comparisons to the GC systems of Local galaxies, we show that …
We present a study of ultra-diffuse galaxies (UDGs) in the Virgo Cluster based on deep imaging from the Next Generation Virgo Cluster Survey (NGVS). Applying a new definition for the UDG class based on galaxy scaling relations, we define samples of 44 and 26 UDGs using expansive and restrictive selection criteria, respectively. Our UDG sample includes objects that are significantly fainter than previously known UDGs: i.e., more than half are fainter than $\langleμ\rangle_e \sim27.5$ mag arcsec$^{-2}$. The UDGs in Virgo's core region show some evidence for being structurally distinct from "norm…
(Abridged) Dynamical friction can be used to distinguish Newtonian gravity and modified Newtonian dynamics (MOND) because it works differently in these frameworks. This concept, however, has yet to be explored very much with MOND. Previous simulations showed weaker dynamical friction during major mergers for MOND than for Newtonian gravity with dark matter. Analytic arguments suggest the opposite for minor mergers. In this work, we verify the analytic predictions for MOND by high-resolution $N$-body simulations of globular clusters (GCs) moving in isolated ultra-diffuse galaxies (UDGs). We tes…
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 $\gtrsim 0.5$ dex above the mean relation at $M_{\rm halo}=10^{10}M_{\odot}$ will host a factor of $\…
We present a kinematic analysis of the globular cluster systems and diffuse stellar light of four intermediate luminosity (sub-$L^{\ast}$) early-type galaxies in the Virgo cluster based on Gemini/GMOS data. Our galaxy sample is fainter ($-23.8<M_K<-22.7$) than most previous studies, nearly doubling the number of galaxies in this magnitude range that now have GC kinematics. The data for the diffuse light extends to $4R_e$, and the data for the globular clusters reaches 8--$12R_e$. We find that the kinematics in these outer regions are all different despite the fact that these four galaxies have…
We present a second set of results from a wide-field photometric survey of the environs of Milky Way globular clusters. The clusters studied are NGC 1261, NGC 1851 and NGC 5824: all have data from DECam on the Blanco 4m telescope. NGC 5824 also has data from the Magellan Clay telescope with MegaCam. We confirm the existence of a large diffuse stellar envelope surrounding NGC 1851 of size at least 240 pc in radius. The radial density profile of the envelope follows a power-law decline with index $γ= -1.5 \pm 0.2$ and the projected shape is slightly elliptical. For NGC 5824 there is no strong de…
Many ultra diffuse galaxies (UDGs) have now been identified in clusters of galaxies. However, the number of nearby UDGs suitable for detailed follow-up remain rare. Our aim is to begin to identify UDGs in the environments of nearby bright early-type galaxies from the VEGAS survey. Here we use a deep g band image of the NGC 5846 group, taken as part of the VEGAS survey, to search for UDGs. We found one object with properties of a UDG if it associated with the NGC 5846 group, which seems likely. The galaxy, we name NGC 5846$\_$UDG1, has an absolute magnitude of M$_g$ = -14.2, corresponding to a …
Formation of globular cluster-rich ultra-diffuse galaxies through mergers
International Centre for Radio Astronomy Research, The University of Western Australia（西澳大利亚大学国际无线电天文研究中心）；National Institute of Technology, Asahikawa College（旭川工业高等专门学校）；ATNF, CSIRO Space and Astronomy（CSIRO空间与天文台射电天文国家设施）；Centre for Astrophysics and Supercomputing, Swinburne University（斯威本科技大学天体物理学与超级计算中心）
Ultra diffuse galaxies (UDGs) reveal extreme properties. Here we compile the largest study to date of 85 globular cluster (GC) systems around UDGs in the Coma cluster, using new deep ground-based imaging of the known UDGs and existing imaging from the Hubble Space Telescope of their GC systems. We find that the richness of GC systems in UDGs generally exceeds that found in normal dwarf galaxies of the same stellar mass. These GC-rich UDGs imply halos more massive than expected from the standard stellar mass-halo mass relation. The presence of such overly massive halos presents a significant ch…
We use data from the HST Coma Cluster Treasury program to assess the richness of the Globular Cluster Systems (GCSs) of 54 Coma ultra-diffuse galaxies (UDGs), 18 of which have a half-light radius exceeding 1.5 kpc. We use a hierarchical Bayesian method tested on a large number of mock datasets to account consistently for the high and spatially varying background counts in Coma. These include both background galaxies and intra-cluster GCs (ICGCs), which are disentangled from the population of member GCs in a probabilistic fashion. We find no candidate for a GCS as rich as that of the Milky Way,…
We present a photometric study of the isolated elliptical NGC 6411 and its globular cluster (GC) system, based on Gemini/GMOS g', r', i' photometry. This galaxy has been the host of a SNIa. Spectral studies indicate an intermediate-age and very metal-rich stellar population in its inner region. The extent of the globular cluster system is about 65 kpc. Its population contains $700\pm45$ members, implying a rather poor system, as normally found for isolated ellipticals. The colour bimodality and luminosity distribution are typical of old GC systems. An excess of bright GCs with intermediate col…
Recently a population of large, very low surface brightness, spheroidal galaxies was identified in the Coma cluster. The apparent survival of these Ultra Diffuse Galaxies (UDGs) in a rich cluster suggests that they have very high masses. Here we present the stellar kinematics of Dragonfly 44, one of the largest Coma UDGs, using a 33.5 hr integration with DEIMOS on the Keck II telescope. We find a velocity dispersion of 47 km/s, which implies a dynamical mass of M_dyn=0.7x10^10 M_sun within its deprojected half-light radius of r_1/2=4.6 kpc. The mass-to-light ratio is M/L=48 M_sun/L_sun, and th…
The so-called ultra-diffuse galaxy NGC~1052-DF2 was announced to be a galaxy lacking dark matter based on a spectroscopic study of its constituent globular clusters. Here we present the first spectroscopic analysis of the stellar body of this galaxy using the MUSE integral-field spectrograph at the (ESO) Very Large Telescope. The MUSE datacube simultaneously provides DF2's stellar velocity field and systemic velocities for seven globular clusters (GCs). We further discovered three planetary nebulae (PNe) that are likely part of this galaxy. While five of the clusters had velocities measured in…
We report the discovery of an extended globular cluster in a halo field in Centaurus A (NGC 5128), situated $\sim 38\kpc$ from the centre of that galaxy, imaged with the Advanced Camera for Surveys on board the Hubble Space Telescope. At the distance of the galaxy, the half-light radius of the cluster is r_h ~ 17pc, placing it among the largest globular clusters known. The faint absolute magnitude of the star cluster, M_(V,o)=-5.2, and its large size render this object somewhat different from the population of extended globular clusters previously reported, making it the first firm detection i…
The last fifteen years have seen the discovery of new types of low-mass stellar systems that bridge the gap between the once well-separated regimes of galaxies and of star clusters. Whether such objects are considered galaxies depends also on the definition of the term "galaxy", and several possible criteria are based on their internal dynamics (e.g. the common concept that galaxies contain dark matter). Moreover, studying the internal dynamics of low-mass stellar systems may also help understand their origin and evolutionary history. The focus of this paper is on two classes of stellar system…
The Spatial Distribution of Globular Cluster Systems in Early Type Galaxies: Estimation Procedure and Catalog of Properties for Globular Cluster Systems Observed with Deep Imaging Surveys
Evidence for the First Globular Cluster Stellar Stream beyond the Milky Way
University of Copenhagen（哥本哈根大学）；DTU Space, Technical University of Denmark（丹麦技术大学空间中心）；Princeton University（普林斯顿大学）；University of Arizona（亚利桑那大学）；Flatiron Institute（平顿研究所）；Northwestern University（西北大学）
Tidally disrupted globular cluster streams are usually observed, and therefore perceived, as narrow, linear and one-dimensional structures in the 6D phase-space. Here we show that the GD-1 stellar stream ($\approx$ 30 pc wide), which is the tidal debris of a disrupted globular cluster, possesses a secondary diffuse and extended stellar component ($\approx$ 100 pc wide) around it, detected at >5$σ$ confidence level. Similar morphological properties are seen in synthetic streams that are produced from star clusters that are formed within dark matter sub-halos and then accrete onto a massive host…
Based upon the kinematics of ten globular clusters, it has recently been claimed that the ultra-diffuse galaxy, NCD 1052-DF2, lacks a significant quantity of dark matter. Dynamical analyses have generally assumed that this galaxy is pressure supported, with the relatively small velocity dispersion of the globular cluster population indicating the deficit of dark matter. However, the presence of a significant rotation of the globular cluster population could substantially modify this conclusion. Here we present the discovery of such a signature of rotation in the kinematics of NGC 1052-DF2's gl…
Lensing flux-ratio anomalies have been frequently observed and taken as evidence for the presence of abundant dark matter substructures in lensing galaxies, as predicted by the cold dark matter (CDM) model of cosmogony. In previous work, we examined the cusp-caustic relations of the multiple images of background quasars lensed by galaxy-scale dark matter haloes, using a suite of high-resolution N-body simulations (the Aquarius simulations). In this work, we extend our previous calculations to incorporate both the baryonic and diffuse dark components in lensing haloes. We include in each lensin…
Recently, \cite{vanDokkum2018} have presented an important discovery of an ultra diffuse galaxy, NGC1052-DF2, with a dark matter content significantly less than predicted from its stellar mass alone. The analysis relies on measured radial velocities of 10 Globular Clusters (GCs), of estimated individual masses of a few $ \times 10^6 M_\odot$. This is about $1\%$ of the inferred mass of NGC1052-DF2 of $2\times 10^8 M_\odot$ within a half-light radius, $R_\mathrm{e}=2.2\, \mathrm{kpc}$. The large relative mass and the old age of these objects imply that they might be susceptible to orbital decay…
