ABSTRACT
We present a new spectroscopic study of 175 stars in the vicinity of the dwarf galaxy Hercules (d ∼ 132 kpc) with data from the Anglo-Australian Telescope and its AAOmega spectrograph ...together with the Two Degree Field multi-object system to solve the conundrum that whether Hercules is tidally disrupting. We combine broad-band photometry, proper motions from Gaia, and our Pristine narrow-band and metallicity-sensitive photometry to efficiently weed out the Milky Way contamination. Such cleaning is particularly critical in this kinematic regime, as both the transverse and heliocentric velocities of Milky Way populations overlap with Hercules. Thanks to this method, three new member stars are identified, including one at almost 10rh of the satellite. All three have velocities and metallicities consistent with that of the main body. Combining this new data set with the entire literature cleaned out from contamination shows that Hercules does not exhibit a velocity gradient (d〈v〉/dχ $= 0.1^{+0.4}_{-0.2}$ km s−1 arcmin−1, 1.6 km s−1 arcmin−1 as a 3σ upper limit) and, as such, does not show evidence to undergo tidal disruption.
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 show that hard encounters in the central regions of globular clusters (GCs) embedded in dark matter (DM) haloes necessarily lead to the formation of gravitationally bound stellar ...envelopes that extend far beyond the nominal tidal radius of the system. Using statistical arguments and numerical techniques, we derive the equilibrium distribution function of stars ejected from the centre of a non-divergent spherical potential. Independently of the velocity distribution with which stars are ejected, GC envelopes have density profiles that approach asymptotically ρ ∼ r−4 at large distances and become isothermal towards the centre. Adding a DM halo component leaves two clear-cut observational signatures: (i) a flattening, or slightly increase of the projected velocity dispersion profile at large distances, and (ii) an outer surface density profile that is systematically shallower than in models with no DM.
Galaxy clusters contain a large population of low-mass dwarf elliptical galaxies whose exact origin is unclear: their colours, structural properties and kinematics differ substantially from those of ...dwarf irregulars in the field. We use the Illustris cosmological simulation to study differences in the assembly histories of dwarf galaxies (3 × 108 < M
*/M⊙ < 1010) according to their environment. We find that cluster dwarfs achieve their maximum total and stellar mass on average ∼8 and ∼4.5 Gyr ago (or redshifts z = 1.0 and 0.4, respectively), around the time of infall into the clusters. In contrast, field dwarfs not subjected to environmental stripping reach their maximum mass at z = 0. These different assembly trajectories naturally produce a colour bimodality, with blue isolated dwarfs and redder cluster dwarfs exhibiting negligible star formation today. The cessation of star formation happens over median times 3.5–5 Gyr depending on stellar mass, and shows a large scatter (∼1–8 Gyr), with the lower values associated with starburst events that occur at infall through the virial radius or pericentric passages. We argue that such starbursts together with the early assembly of cluster dwarfs can provide a natural explanation for the higher specific frequency of globular clusters (GCs) in cluster dwarfs, as found observationally. We present a simple model for the formation and stripping of GCs that supports this interpretation. The origin of dwarf ellipticals in clusters is, therefore, consistent with an environmentally driven evolution of field dwarf irregulars. However, the z = 0 field analogues of cluster dwarf progenitors have today stellar masses a factor of ∼3 larger – a difference arising from the early truncation of star formation in cluster dwarfs.
ABSTRACT
We use the photometric metallicities provided by the panoramic Pristine survey to study the veracity and derive the metallicities of the numerous stellar streams found by the application of ...the STREAMFINDER algorithm to the Gaia Early Data Release 3 data. All 26 streams present in Pristine show a clear metallicity distribution function, which provides an independent check of the reality of these structures, supporting the reliability of STREAMFINDER in finding streams and the power of Pristine to measure precise metallicities. We further present six candidate structures with coherent phase-space and metallicity signals that are very likely streams. The majority of studied streams are very metal-poor (14 structures with Fe/H < −2.0) and include three systems with Fe/H < −2.9 (C-11, C-19, and C-20). These streams could be the closest debris of low-luminosity dwarf galaxies or may have originated from globular clusters of significantly lower metallicity than any known current Milky Way globular cluster. Our study shows that the promise of the Gaia data for Galactic Archeology studies can be substantially strengthened by quality photometric metallicities, allowing us to peer back into the earliest epochs of the formation of our Galaxy and its stellar halo constituents.
ABSTRACT We report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded u-, g-, and i-band image obtained with the Dark Energy Camera ...wide-field camera mounted on the 4-m Blanco telescope at the Cerro Tololo Interamerican Observatory as part of the Next Generation Fornax Survey (NGFS). The new dwarf galaxies have quasi-exponential light profiles, effective radii 0.1 < re < 2.8 kpc, and average effective surface brightness values 22.0 < i < 28.0 mag arcsec−2. We confirm the existence of ultra-diffuse galaxies (UDGs) in the Fornax core regions that resemble counterparts recently discovered in the Virgo and Coma galaxy clusters. We also find extremely low surface brightness NGFS dwarfs, which are several magnitudes fainter than the classical UDGs. The faintest dwarf candidate in our NGFS sample has an absolute magnitude of Mi = −8.0 mag. The nucleation fraction of the NGFS dwarf galaxy sample appears to decrease as a function of their total luminosity, reaching from a nucleation fraction of >75% at luminosities brighter than Mi −15.0 mag to 0% at luminosities fainter than Mi −10.0 mag. The two-point correlation function analysis of the NGFS dwarf sample shows an excess on length scales below ∼100 kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core.
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 the literature, we were able to confirm the membership of two more candidates through precise radial velocity measurements, which increases the measured specific frequency of GCs in DF2. The mean velocity of the diffuse stellar body, 1792.9
+1.4
−1.8
km s
−1
, is consistent with the mean globular cluster velocity. We detect a weak but significant velocity gradient within the stellar body, with a kinematic axis close to the photometric major axis, making it a prolate-like rotator. We estimate a velocity dispersion from the clusters and PNe of
σ
int
= 10.6
−2.3
+3.9
km s
−1
. The velocity dispersion
σ
DF2⋆
(
R
e
) for the stellar body within one effective radius is 10.8
+3.2
−4.0
km s
−1
. Considering various sources of systemic uncertainties, this central value varies between 5 and 13 km s
−1
, and we conservatively report a 95% confidence upper limit to the dispersion within one
R
e
of 21 km s
−1
. We provide updated mass estimates based on these dispersions corresponding to the different distances to NGC 1052-DF2 that have been reported in the recent literature.
The spheroid of the Sombrero galaxy, NGC 4594, is considered a prototype of classical, merger-built bulges. We use a Spitzer IRAC 3.6-
image to perform a detailed structural analysis of this galaxy. ...If one fits to this image only bulge and disc components, the bulge occupies a locus in the mass-size relation close to that of elliptical galaxies. When an outer stellar spheroid is added to improve the fit, the bulge Sérsic index drops by a factor of ≈2, and, if taken at face value, could mean that this bulge is actually a disc-like, pseudo-bulge, or a bar viewed end-on. The bulge effective radius and the bulge-to-total ratio also drop dramatically, putting the bulge in a position closer to that of bulges in the mass-size relation. We discuss implications from these findings, including the locus of the Sombrero bulge in the black hole mass versus bulge mass relation. With this new bulge mass estimate, current dynamical estimates for the mass of the central black hole in Sombrero are more than 10 times larger than expected, if only the bulge mass is considered. A better agreement is found if the sum of bulge and outer spheroid masses is considered. Furthermore, residual images show the presence of a stellar ring and a stellar, inner ring or disc, with unprecedented clarity. We also show that Sombrero is an outlier in scaling relations of disc galaxies involving the disc, the spheroid and the globular cluster system, but not so when its structural components are considered independently. In this context, the globular cluster system of Sombrero might not be representative of disc galaxies. Finally, we discuss the possibility that Sombrero formed as an elliptical galaxy but accreted a massive disc, which itself has secularly evolved, resulting in a complex and peculiar system.
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 Mass Assembly of early-Type GaLAxies with their fine Structures (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 environments, although 61% of the sample fall within the virial radii of groups. Based on a detailed analysis of their photometric and structural properties, we find that the MATLAS UDGs do not show significant differences from the traditional dwarfs, except from the predefined size and surface brightness cut. Their median color is as red as the one measured in galaxy clusters, albeit with a narrower color range. The majority of the UDGs are visually classified as dwarf ellipticals with log stellar masses of ∼6.5 − 8.7. The fraction of nucleated UDGs (∼34%) is roughly the same as the nucleated fraction of the traditional dwarfs. Only five (∼8%) UDGs show signs of tidal disruption and only two are tidal dwarf galaxy candidates. A study of globular cluster (GC) candidates selected in the CFHT images finds no evidence of a higher GC specific frequency
S
N
for UDGs than for classical dwarfs, contrary to what is found in most clusters. The UDG halo-to-stellar mass ratio distribution, as estimated from the GC counts, peaks at roughly the same value as for the traditional dwarfs, but spans the smaller range of ∼10 − 2000. We interpret these results to mean that the large majority of the field-to-group UDGs do not have a different formation scenario than traditional dwarfs.
It was first observed in the 1970s that the dwarf galaxies surrounding our Milky Way, so-called satellites, appear to be arranged in a thin, vast plane. Similar discoveries have been made around ...additional galaxies in the local Universe such as Andromeda, Centaurus A, and potentially M83. In the specific cases with available kinematic data, the dwarf satellites also appear to preferentially co-orbit their massive host galaxy. Planes of satellites are rare in the lambda cold dark matter paradigm, although they may be a natural consequence of projection effects. Such a phase-space correlation, however, remains difficult to explain. In this work we analyzed the 2D spatial distribution of 2210 dwarf galaxies around early-type galaxies (ETGs) in the low-to-medium density fields of the “Mass Assembly of early-Type GaLAxies with their fine Structures” (MATLAS) survey. Under the assumption that the dwarfs are satellite members of the central massive ETG, we identified flattened structures using both a variation in the Hough transform and total least square fitting. In 119 satellite systems, we find 31 statistically significant flattened dwarf structures using a combination of both methods with subsequent Monte Carlo simulations with random data. The vast majority of these dwarf structures lie within the estimated virial radii of the massive host. The major axes of these systems are aligned better than 30° with the estimated orientation of the large-scale structure in nine (50%) cases. Additional distance measurements and future kinematic studies will be required to confirm the planar nature of these structures and to determine if they are corotating systems.
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