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.
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.
ABSTRACT We use imaging from the Next Generation Virgo cluster Survey (NGVS) to present a comparative study of ultra-compact dwarf (UCD) galaxies associated with three prominent Virgo sub-clusters: ...those centered on the massive red-sequence galaxies M87, M49, and M60. We show how UCDs can be selected with high completeness using a combination of half-light radius and location in color-color diagrams (u*iKs or u*gz). Although the central galaxies in each of these sub-clusters have nearly identical luminosities and stellar masses, we find large differences in the sizes of their UCD populations, with M87 containing ∼3.5 and 7.8 times more UCDs than M49 and M60, respectively. The relative abundance of UCDs in the three regions scales in proportion to sub-cluster mass, as traced by X-ray gas mass, total gravitating mass, number of globular clusters (GCs), and number of nearby galaxies. We find that the UCDs are predominantly blue in color, with ∼85% of the UCDs having colors similar to blue GCs and stellar nuclei of dwarf galaxies. We present evidence that UCDs surrounding M87 and M49 may follow a morphological sequence ordered by the prominence of their outer, low surface brightness envelope, ultimately merging with the sequence of nucleated low-mass galaxies, and that envelope prominence correlates with distance from either galaxy. Our analysis provides evidence that tidal stripping of nucleated galaxies is an important process in the formation of UCDs.
Intracluster (IC) populations are expected to be a natural result of the hierarchical assembly of clusters, yet their low space densities make them difficult to detect and study. We present the first ...definitive kinematic detection of an IC population of globular clusters (GCs) in the Virgo cluster, around the central galaxy M87. This study focuses on the Virgo core, for which the combination of Next Generation Virgo Cluster Survey photometry and follow-up spectroscopy allows us to reject foreground star contamination and explore GC kinematics over the full Virgo dynamical range. The GC kinematics changes gradually with galactocentric distance, decreasing in mean velocity and increasing in velocity dispersion, eventually becoming indistinguishable from the kinematics of Virgo dwarf galaxies at R > 320 kpc. By kinematically tagging M87 halo and intracluster GCs, we find that (1) the M87 halo has a smaller fraction (52 3%) of blue clusters with respect to the IC counterpart (77 10%), (2) the (g′−r′)0 versus (i′−z′)0 color-color diagrams reveal a galaxy population that is redder than the IC population, which may be due to a different composition in chemical abundance and progenitor mass, and (3) the ICGC distribution is shallower and more extended than the M87 GCs, yet still centrally concentrated. The ICGC specific frequency, SN,ICL = 10.2 4.8, is consistent with what is observed for the population of quenched, low-mass galaxies within 1 Mpc from the cluster's center. The IC population at Virgo's center is thus consistent with being an accreted component from low-mass galaxies tidally stripped or disrupted through interactions, with a total mass of .
Large samples of globular clusters (GC) with precise multi-wavelength photometry are becoming increasingly available and can be used to constrain the formation history of galaxies. We present the ...results of an analysis of Milky Way (MW) and Virgo core GCs based on 5 optical-near-infrared colors and 10 synthetic stellar population models. For the MW GCs, the models tend to agree on photometric ages and metallicities, with values similar to those obtained with previous studies. When used with Virgo core GCs, for which photometry is provided by the Next Generation Virgo cluster Survey (NGVS), the same models generically return younger ages. This is a consequence of the systematic differences observed between the locus occupied by Virgo core GCs and models in panchromatic color space. Only extreme fine-tuning of the adjustable parameters available to us can make the majority of the best-fit ages old. Although we cannot exclude that the formation history of the Virgo core may lead to more conspicuous populations of relatively young GCs than in other environments, we emphasize that the intrinsic properties of the Virgo GCs are likely to differ systematically from those assumed in the models. Thus, the large wavelength coverage and photometric quality of modern GC samples, such as those used here, is not by itself sufficient to better constrain the GC formation histories. Models matching the environment-dependent characteristics of GCs in multi-dimensional color space are needed to improve the situation.
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.
The NGVS-IR project (Next Generation Virgo Cluster Survey-Infrared) is a contiguous, near-infrared imaging survey of the Virgo cluster of galaxies. It complements the optical wide-field survey of ...Virgo (NGVS). In its current state, NGVS-IR consists of Ks-band imaging of 4 deg2 centered on M87 and J- and Ks-band imaging of ~16 deg2 covering the region between M49 and M87.We present observations of the central 4 deg2 centered on Virgo's core region. The data were acquired with WIRCam on the Canada-France-Hawaii Telescope, and the total integration time was 41 hr distributed over 34 contiguous tiles. Combining the Ks data with optical and ultraviolet data, we build the uiKsubs color-color diagram, which allows a very clean color-based selection of globular clusters in Virgo. Equipped with a powerful new tool, future NGVS-IR investigations based on the uiKsubs diagram will address the mapping and analysis of extended structures and compact stellar systems in and around Virgo galaxies.
Faint dwarf galaxies in Hickson Compact Group 90 Ordenes-Briceno, Yasna; Taylor, Matthew A; Puzia, Thomas H ...
Monthly Notices of the Royal Astronomical Society,
12/2016, Letnik:
463, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We report the discovery of a very diverse set of five low-surface brightness (LSB) dwarf galaxy candidates in Hickson Compact Group 90 (HCG 90) detected in deep U- and I-band images obtained with ...Very Large Telescope/Visible Multi-Object Spectrograph. These are the first LSB dwarf galaxy candidates found in a compact group of galaxies. We measure spheroid half-light radii in the range 0.7 ... r sub( eff)/kpc ... 1.5 with luminosities of -11.65 ... M... -9.42 and -12.79 ... M sub( I) ... -10.58 mag, corresponding to a colour range of (U - I) sub( 0) ... 1.1-2.2 mag and surface brightness levels of ... 28.1 mag arcsec super( -2) and ... 27.4 mag arcsec super( -2). Their colours and luminosities are consistent with a diverse set of stellar population properties. Assuming solar and 0.02...Z... metallicities we obtain stellar masses in the range M*... 10 super( 5.7 - 6.3) M... and M*... 10 super( 6.3-8) M... Three dwarfs are older than 1 Gyr, while the other two significantly bluer dwarfs are younger than ~2 Gyr at any mass/metallicity combination. Altogether, the new LSB dwarf galaxy candidates share properties with dwarf galaxies found throughout the Local Volume and in nearby galaxy clusters such as Fornax. We find a pair of candidates with ~2 kpc projected separation, which may represent one of the closest dwarf galaxy pairs found. We also find a nucleated dwarf candidate, with a nucleus size of r sub( eff) ... 46-63 pc and magnitude M sub( U, 0) = -7.42 mag and (U - I) sub( 0) = 1.51 mag, which is consistent with a nuclear stellar disc with a stellar mass in the range 10 super( 4.9 - 6.5) M... (ProQuest: ... denotes formulae/symbols omitted.)
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.
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