ABSTRACT
We reliably extend the stellar mass–size relation over 0.2 ≤ z ≤ 2 to low stellar mass galaxies by combining the depth of Hubble Frontier Fields with the large volume covered by CANDELS. ...Galaxies are simultaneously modelled in multiple bands using the tools developed by the MegaMorph project, allowing robust size (i.e. half-light radius) estimates even for small, faint, and high redshift galaxies. We show that above 107 M⊙, star-forming galaxies are well represented by a single power law on the mass–size plane over our entire redshift range. Conversely, the stellar mass–size relation is steep for quiescent galaxies with stellar masses $\ge 10^{10.3}\, {\rm M}_\odot$ and flattens at lower masses, regardless of whether quiescence is selected based on star-formation activity, rest-frame colours, or structural characteristics. This flattening occurs at sizes of ∼1 kpc at z ≤ 1. As a result, a double power law is preferred for the stellar mass–size relation of quiescent galaxies, at least above 10$^7\, {\rm M}_\odot$. We find no strong redshift dependence in the slope of the relation of star-forming galaxies as well as of high mass quiescent galaxies. We also show that star-forming galaxies with stellar masses $\ge 10^{9.5}\, {\rm M}_\odot$ and quiescent galaxies with stellar masses $\ge 10^{10.3}\, {\rm M}_\odot$ have undergone significant size growth since z ∼ 2, as expected; however, low mass galaxies have not. Finally, we supplement our data with predominantly quiescent dwarf galaxies from the core of the Fornax cluster, showing that the stellar mass–size relation is continuous below 10$^7\, {\rm M}_\odot$, but a more complicated functional form is necessary to describe the relation.
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 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.
Abstract
New wide-field u
΄
g
΄
r
΄
i
΄
z
΄
Dark Energy Camera observations centred on the nearby giant elliptical galaxy NGC 5128 covering ∼21 deg2 are used to compile a new catalogue of ∼3200 ...globular clusters (GCs). We report 2404 newly identified candidates, including the vast majority within ∼140 kpc of NGC 5128. We find evidence for a transition at a galactocentric radius of R
gc ≈ 55 kpc from GCs ‘intrinsic’ to NGC 5128 to those likely to have been accreted from dwarf galaxies or that may transition to the intragroup medium of the Centaurus A galaxy group. We fit power-law surface number density profiles of the form
$\Sigma _{N, R_{\rm gc}}\propto R_{\rm gc}^\Gamma$
and find that inside the transition radius, the red GCs are more centrally concentrated than the blue, with Γinner, red ≈ −1.78 and Γinner, blue ≈ −1.40, respectively. Outside this region both profiles flatten, more dramatically for the red GCs (Γouter, red ≈ −0.33) compared to the blue (Γouter, blue ≈ −0.61), although the former is more likely to suffer contamination by background sources. The median (g
΄ − z
΄)0 = 1.27 mag colour of the inner red population is consistent with arising from the amalgamation of two giant galaxies each less luminous than present-day NGC 5128. Both inwards and outwards of the transition radius, we find the fraction of blue GCs to dominate over the red GCs, indicating a lively history of minor mergers. Assuming the blue GCs to originate primarily in dwarf galaxies, we model the population required to explain them, while remaining consistent with NGC 5128’s present-day spheroid luminosity. We find that several dozen dwarfs of luminosities L
dw, V
≃ 106–9.3 L
V, ⊙, following a Schechter luminosity function with a faint-end slope of −1.50 ≲ α ≲ −1.25 is favoured, many of which may have already been disrupted in NGC 5128’s tidal field.
We present deep Hα imaging of seven Hickson Compact Groups (HCGs) using the 4.1-m Southern Astrophysics Research (SOAR) Telescope. The high spatial resolution of the observations allows us to study ...both the integrated star formation properties of the main galaxies as well as the 2D distribution of star-forming knots in the faint tidal arms that form during interactions between the individual galaxies. We derive star formation rates and stellar masses for group members and discuss their position relative to the main sequence of star-forming galaxies. Despite the existence of tidal features within the galaxy groups, we do not find any indication for enhanced star formation in the selected sample of HCGs. We study azimuthally averaged Hα profiles of the galaxy discs and compare them with the g′ and r′ surface brightness profiles. We do not find any truncated galaxy discs but reveal that more massive galaxies show a higher light concentration in Hα than less massive ones. We also see that galaxies that show a high light concentration in r′, show a systematic higher light concentration in Hα. Tidal dwarf galaxy (TDG) candidates have been previously detected in R-band images for two groups in our sample but we find that most of them are likely background objects as they do not show any emission in Hα. We present a new TDG candidate at the tip of the tidal tail in HCG 91.
The central region of the giant low-surface-brightness galaxy (GLSBG) Malin 1 has long been known to have a complex morphology, with evidence of a bulge, disc, and potentially a bar hosting ...asymmetric star formation. In this work, we use VLT/MUSE data to resolve the central region of Malin 1 in order to determine its structure. We used careful light profile fitting in every image slice of the datacube to create wavelength-dependent models of each morphological component, from which we were able to cleanly extract their spectra. We then used the kinematics and emission line properties from these spectra to better understand the nature of each component extracted from our model fitting. We report the detection of a pair of distinct sources at the centre of this galaxy with a separation of $ which corresponds to a separation on sky of $ kpc. The radial velocity data of each object confirm that they both lie in the kinematic core of the galaxy. An analysis of the emission lines reveals that the central compact source is more consistent with being ionised through star formation and/or a LINER, while the off-centre compact source lies closer to the separation between star-forming galaxies and active galacic nuclei (AGNs). This evidence suggests that the centre of Malin 1 hosts either a bar with asymmetric star formation or two distinct components. In the latter scenario, we propose two hypotheses for the nature of the off-centre compact source- it could either be a star-forming clump, containing one or more star clusters, that is in the process of falling into the core of the galaxy and eventually merging with the central nuclear star cluster, or it could be a clump of gas falling into the centre of the galaxy from either outside or from the disc and triggering star formation there.
ABSTRACT
Clues to the formation and evolution of nuclear star clusters (NSCs) lie in their stellar populations. However, these structures are often very faint compared to their host galaxy, and ...spectroscopic analysis of NSCs is hampered by contamination of light from the rest of the system. With the introduction of wide-field integral field unit (IFU) spectrographs, new techniques have been developed to model the light from different components within galaxies, making it possible to cleanly extract the spectra of the NSCs and study their properties with minimal contamination from the light of the rest of the galaxy. This work presents the analysis of the NSCs in a sample of 12 dwarf galaxies in the Fornax Cluster observed with the Multi-Unit Spectroscopic Explorer (MUSE). Analysis of the stellar populations and star formation histories reveal that all the NSCs show evidence of multiple episodes of star formation, indicating that they have built up their mass further since their initial formation. The NSCs were found to have systematically lower metallicities than their host galaxies, which is consistent with a scenario for mass assembly through mergers with infalling globular clusters, whilst the presence of younger stellar populations and gas emission in the core of two galaxies is indicative of in-situ star formation. We conclude that the NSCs in these dwarf galaxies likely originated as globular clusters that migrated to the core of the galaxy that have built up their mass mainly through mergers with other infalling clusters, with gas-inflow leading to in-situ star formation playing a secondary role.
We present the analysis of 61 nucleated dwarf galaxies in the central regions ( Rvir/4) of the Fornax galaxy cluster. The galaxies and their nuclei are studied as part of the Next Generation Fornax ...Survey using optical imaging obtained with the Dark Energy Camera mounted at Blanco/Cerro Tololo Inter-American Observatory and near-infrared data obtained with VIRCam at VISTA/ESO. We decompose the nucleated dwarfs in nucleus and spheroid, after subtracting the surface brightness profile of the spheroid component and studying the nucleus using point source photometry. In general, nuclei are consistent with colors of confirmed metal-poor globular clusters, but with significantly smaller dispersion than other confirmed compact stellar systems in Fornax. We find a bimodal nucleus mass distribution with peaks located at and ∼6.3. These two nucleus subpopulations have different stellar population properties: the more massive nuclei are older than ∼2 Gyr and have metal-poor stellar populations (Z ≤ 0.02 Z ), while the less massive nuclei are younger than ∼2 Gyr with metallicities in the range 0.02 < Z/Z ≤ 1. We find that the nucleus mass ( ) versus galaxy mass ( ) relation becomes shallower for less massive galaxies starting around 108 M , and the mass ratio shows a clear anticorrelation with for the lowest masses, reaching 10%. We test current theoretical models of nuclear cluster formation and find that they cannot fully reproduce the observed trends. A likely mixture of in situ star formation and star cluster mergers seems to be acting during nucleus growth over cosmic time.
We derive stellar population parameters for a representative sample of ultracompact dwarfs (UCDs) and a large sample of massive globular clusters (GCs) with stellar masses 106 M in the central galaxy ...M87 of the Virgo galaxy cluster, based on model fitting to the Lick-index measurements from both the literature and new observations. After necessary spectral stacking of the relatively faint objects in our initial sample of 40 UCDs and 118 GCs, we obtain 30 sets of Lick-index measurements for UCDs and 80 for GCs. The M87 UCDs have ages 8 Gyr and /Fe 0.4 dex, in agreement with previous studies based on smaller samples. The literature UCDs, located in lower-density environments than M87, extend to younger ages and smaller /Fe (at given metallicities) than M87 UCDs, resembling the environmental dependence of the stellar nuclei of dwarf elliptical galaxies (dEs) in the Virgo cluster. The UCDs exhibit a positive mass-metallicity relation (MZR), which flattens and connects compact ellipticals at stellar masses 108 M . The Virgo dE nuclei largely follow the average MZR of UCDs, whereas most of the M87 GCs are offset toward higher metallicities for given stellar masses. The difference between the mass-metallicity distributions of UCDs and GCs may be qualitatively understood as a result of their different physical sizes at birth in a self-enrichment scenario or of galactic nuclear cluster star formation efficiency being relatively low in a tidal stripping scenario for UCD formation. The existing observations provide the necessary but not sufficient evidence for tidally stripped dE nuclei being the dominant contributors to the M87 UCDs.
We report the discovery of 271 previously undetected dwarf galaxies in the outer Fornax cluster regions at radii rvir/4 < r < rvir/2 using data from the Next Generation Fornax Survey (NGFS) with deep ...coadded u′, g′, and i′ images obtained with Blanco/DECam at Cerro Tololo Interamerican Observatory. From the 271 dwarf candidates, we find 39 to be nucleated. Together with our previous study of the central Fornax region, the new dwarfs detected with NGFS data number 392, of which 56 are nucleated. The total Fornax dwarf galaxy population from NGFS and other catalogs rises, therefore, to a total of 643 with 181 being nucleated, yielding an overall nucleation fraction of 28%. The absolute i′-band magnitudes for the outer NGFS dwarfs are in the range −18.80 ≤ Mi′ ≤ −8.78 with effective radii reff,i′ = 0.18-2.22 kpc and an average Sérsic index . Nonnucleated dwarfs are found to be fainter and smaller by mag and than the nucleated dwarfs. We demonstrate a significant clustering of dwarf galaxies on scales 100 kpc, and projected surface number density profile estimates, N(r), show a concentration of dwarfs in the Fornax core region within r 350 kpc. N(r) has a flat distribution up to ∼350 kpc, beyond which it declines for the nonnucleated dwarfs. The nucleated dwarfs have a steeper N(r) distribution, are more concentrated toward NGC 1399, and are decreasing rapidly outwards. This is the first time the transition from cluster to field environment has been established for the very faint dwarf galaxy population with robust sample statistics.
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