Abstract
A particular population of galaxies have drawn much interest recently, which are as faint as typical dwarf galaxies but have the sizes as large as L* galaxies, the so called ultradiffuse ...galaxies (UDGs). The lack of tidal features of UDGs in dense environments suggests that their host haloes are perhaps as massive as that of the Milky Way. On the other hand, galaxy formation efficiency should be much higher in the haloes of such masses. Here, we use the model galaxy catalogue generated by populating two large simulations: the Millennium-II cosmological simulation and Phoenix simulations of nine big clusters with the semi-analytic galaxy formation model. This model reproduces remarkably well the observed properties of UDGs in the nearby clusters, including the abundance, profile, colour and morphology, etc. We search for UDG candidates using the public data and find two UDG candidates in our Local Group and 23 in our Local Volume, in excellent agreement with the model predictions. We demonstrate that UDGs are genuine dwarf galaxies, formed in the haloes of ∼1010 M⊙. It is the combination of the late formation time and high spins of the host haloes that results in the spatially extended feature of this particular population. The lack of tidal disruption features of UDGs in clusters can also be explained by their late infall-time.
We present a photometric study of the dwarf galaxy population in the core region ( rvir/4) of the Fornax galaxy cluster based on deep u′g′i′ photometry from the Next Generation Fornax Cluster Survey. ...All imaging data were obtained with the Dark Energy Camera mounted on the 4 m Blanco telescope at the Cerro Tololo Interamerican Observatory. We identify 258 dwarf galaxy candidates with luminosities −17 Mg′ −8 mag, corresponding to typical stellar masses of , reaching ∼3 mag deeper in point-source luminosity and ∼4 mag deeper in surface brightness sensitivity compared to the classic Fornax Cluster Catalog. Morphological analysis shows that the dwarf galaxy surface-brightness profiles are well represented by single-component Sérsic models with average Sérsic indices of and average effective radii of . Color-magnitude relations indicate a flattening of the galaxy red sequence at faint galaxy luminosities, similar to the one recently discovered in the Virgo cluster. A comparison with population synthesis models and the galaxy mass-metallicity relation reveals that the average faint dwarf galaxy is likely older than ∼5 Gyr. We study galaxy scaling relations between stellar mass, effective radius, and stellar mass surface density over a stellar mass range covering six orders of magnitude. We find that over the sampled stellar mass range several distinct mechanisms of galaxy mass assembly can be identified: (1) dwarf galaxies assemble mass inside the half-mass radius up to , (2) isometric mass assembly occurs in the range , and (3) massive galaxies assemble stellar mass predominantly in their halos at and above.
Abstract
We present a photometric analysis of globular cluster 47 Tuc (NGC 104) using near-IR imaging data from the GeMS/GSAOI Galactic Globular Cluster Survey (G4CS), which is in operation at ...Gemini-South telescope. Our survey is designed to obtain AO-assisted deep imaging with near diffraction-limited spatial resolution of the central fields of Milky Way globular clusters. The G4CS near-IR photometry was combined with an optical photometry catalog that was obtained from Hubble Space Telescope survey data to produce a high-quality color–magnitude diagram that reaches down to
K
s
≈ 21 Vega mag. We used the software suite BASE-9, which uses an adaptive Metropolis sampling algorithm to perform a Markov chain Monte Carlo Bayesian analysis, and obtained probability distributions and precise estimates for the age, distance, and extinction cluster parameters. Our best estimate for the age of 47 Tuc is
12.42
−
0.05
+
0.05
± 0.08 Gyr and our true distance modulus estimate is (
m
−
M
)
0
= 13.250
−
0.003
+
0.003
± 0.028 mag, which are in tight agreement with previous studies using Gaia DR2 parallax and detached eclipsing binaries.
We present new blue straggler star (BSS) catalogues in 38 Milky Way globular clusters (GCs) based on multipassband and multi-epoch treasury survey data from the Hubble Space Telescope. We measure ...precise astrometry and relative proper motions of stars in all target clusters and performed a subsequent cluster membership selection. We study the accuracy of our proper-motion measurements using estimates of central velocity dispersions and find very good agreement with previous studies in the literature. Finally, we present a homogeneous BSS selection method, that expands the classic BSS selection parameter space to more evolved BSS evolutionary stages. We apply this method to the proper-motion cleaned GC star catalogues in order to define proper-motion cleaned BSS catalogues in all 38 GCs, which we make publicly available to enable further study and follow-up observations.
The Pan-Andromeda Archaeological Survey is a survey of >400 square degrees centered on the Andromeda (M31) and Triangulum (M33) galaxies that has provided the most extensive panorama of an L galaxy ...group to large projected galactocentric radii. Here, we collate and summarize the current status of our knowledge of the substructures in the stellar halo of M31, and discuss connections between these features. We estimate that the 13 most distinctive substructures were produced by at least 5 different accretion events, all in the last 3 or 4 Gyr. We suggest that a few of the substructures farthest from M31 may be shells from a single accretion event. We calculate the luminosities of some prominent substructures for which previous estimates were not available, and we estimate the stellar mass budget of the outer halo of M31. We revisit the problem of quantifying the properties of a highly structured data set; specifically, we use the OPTICS clustering algorithm to quantify the hierarchical structure of M31's stellar halo and identify three new faint structures. M31's halo, in projection, appears to be dominated by two "mega-structures," which can be considered as the two most significant branches of a merger tree produced by breaking M31's stellar halo into increasingly smaller structures based on the stellar spatial clustering. We conclude that OPTICS is a powerful algorithm that could be used in any astronomical application involving the hierarchical clustering of points. The publication of this article coincides with the public release of all PAndAS data products.
We investigate the origin of the shape of the globular cluster (GC) system scaling parameters as a function of galaxy mass, i.e. specific frequency (SN), specific luminosity (SL), specific mass (SM) ...and specific number () of GCs. In the low-mass galaxy regime (MV≳−16 mag), our analysis is based on Hubble Space Telescope/Advanced Camera for Surveys observations of GC populations of faint, mainly late-type dwarf galaxies in low-density environments. In order to sample the entire range in galaxy mass (MV=−11 to −23 mag =106– 1011 L⊙), environment and morphology we augment our sample with data of spiral and elliptical galaxies from the literature, in which old GCs are reliably detected. This large data set confirms (irrespective of the galaxy type) the increase in the specific frequencies of GCs above and below a galaxy magnitude of MV≃−20 mag. Over the full mass range, the SL value of early-type galaxies is, on average, twice that of late types. To investigate the observed trends, we derive theoretical predictions of GC system scaling parameters as a function of host galaxy mass based on the models of Dekel and Birnboim in which star formation processes are regulated by stellar and supernova feedback below a stellar mass of 3 × 1010 M⊙ and by virial shocks above it. We find that the analytical model describes remarkably well the shape of the GC system scaling parameter distributions with a universal specific GC formation efficiency, η, which relates the total mass in GCs to the total galaxy halo mass. Early-type and late-type galaxies show a similar mean value of η= 5.5 × 10−5, with an increasing scatter towards lower galaxy masses. This can be due to the enhanced stochastic nature of the star and star-cluster formation processes for such systems. Some massive galaxies have excess η values compared to what is expected from the mean model prediction for galaxies more luminous than MV≃−20 mag (LV≳ 1010 L⊙). This may be attributed to a very efficient early GC formation, less efficient production of field stars, accretion of predominantly low-mass/luminosity high-η galaxies or a mixture of all these effects.
Abstract
We use the Wide Field Camera 3 onboard the Hubble Space Telescope to obtain deep, high-resolution photometry of the young (∼100 Myr) star cluster NGC 1850 in the Large Magellanic Cloud. We ...analyse the cluster colour–magnitude diagram (CMD) and find that it hosts an extended main-sequence turn-off (MSTO) and a double main sequence (MS). We demonstrate that these features cannot be due to photometric errors, field star contamination or differential reddening. From a comparison with theoretical models and Monte Carlo simulations, we show that a coeval stellar population featuring a distribution of stellar rotation rates can reproduce the MS split quite well. However, it cannot reproduce the observed MSTO region, which is significantly wider than the simulated ones. Exploiting narrow-band Hα imaging, we find that the MSTO hosts a population of Hα-emitting stars that are interpreted as rapidly rotating Be-type stars. We explore the possibility that the discrepancy between the observed MSTO morphology and that of the simulated simple stellar population (SSP) is caused by the fraction of these objects that are highly reddened, but we rule out this hypothesis. We demonstrate that the global CMD morphology is well reproduced by a combination of SSPs that covers an age range of ∼35 Myr as well as a wide variety of rotation rates. We derive the cluster mass and escape velocity, and use dynamical evolution models to predict their evolution starting at an age of 10 Myr. We discuss these results and their implications in the context of the extended MSTO phenomenon.
Using deep, high-resolution optical imaging from the Next Generation Virgo Cluster Survey, we study the properties of nuclear star clusters (NSCs) in a sample of nearly 400 quiescent galaxies in the ...core of Virgo with stellar masses 105 / 1012. The nucleation fraction reaches a peak value fn 90% for 109 galaxies and declines for both higher and lower masses, but nuclei populate galaxies as small as 5 × 105 . Comparison with literature data for nearby groups and clusters shows that at the low-mass end nucleation is more frequent in denser environments. The NSC mass function peaks at MNSC 7 × 105 , a factor 3-4 times larger than the turnover mass for globular clusters (GCs). We find a nonlinear relation between the stellar masses of NSCs and those of their host galaxies, with a mean nucleus-to-galaxy mass ratio that drops to MNSC/M 3.6 × 10−3 for 5 × 109 galaxies. Nuclei in both more and less massive galaxies are much more prominent: at the low-mass end, where nuclei are nearly 50% as massive as their hosts. We measure an intrinsic scatter in NSC masses at a fixed galaxy stellar mass of 0.4 dex, which we interpret as evidence that the process of NSC growth is significantly stochastic. At low galaxy masses we find a close connection between NSCs and GC systems, including very similar occupation distributions and comparable total masses. We discuss these results in the context of current dissipative and dissipationless models of NSC formation.
The globular cluster (GC) specific frequency (SN), 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 < Mz < −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, = (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.
Abstract
The Next Generation Virgo Cluster Survey (NGVS) was designed to provide a deep census of baryonic structures in the Virgo cluster. The survey covers the 104 deg
2
area from the core of Virgo ...out to one virial radius, in the
u
*
griz
bandpasses, to a point-source depth of
g
∼ 25.9 mag (10
σ
) and a single pixel surface brightness limit of
μ
g
∼ 29 mag arcsec
−2
(2
σ
above the sky). Here we present the final catalog of 404 Virgo galaxies located within a 3.71 deg
2
(0.3 Mpc
2
) region centered on M87, Virgo’s dominant galaxy. Of these, 154 were previously uncataloged and span the range 17.8 mag <
g
< 23.7 mag (−13.4 mag <
M
g
< −7.4 mag at the 16.5 Mpc distance of Virgo). Extensive simulations show that the NGVS catalog is complete down to
g
= 18.6 mag (
M
g
= −12.5 mag, corresponding to a stellar mass
for an old stellar population), and 50% complete at
g
= 22.0 mag (
M
g
= −9.1 mag,
). The NGVS 50% completeness limit is 3 mag deeper than that of the Virgo Cluster Catalog (VCC), which has served as Virgo’s reference standard for over a quarter century, and 2 mag deeper than the VCC detection limit. We discuss the procedure adopted for the identification of objects and the criteria used to assess cluster membership. For each of the 404 galaxies in the NGVS Virgo Cluster core catalog, we present photometric and structural parameters based on a nonparametric curve-of-growth and isophotal analysis, as well as parametric (Sérsic, double-Sérsic, and/or core-Sérsic) fits to the one-dimensional surface brightness profiles and two-dimensional light distributions.
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