ABSTRACT We study the intrinsic shapes of a sample of over 400 quiescent galaxies in the cores of the Virgo and Fornax clusters with luminosities 106 ≤ Lg/L⊙ ≤ 108. Similar to satellites of the Local ...Group and Centaurus A, these faint, low surface brightness cluster galaxies are best described as a family of thick (〈C/A〉 > 0.5), oblate-triaxial spheroids. However, the large sample size allows us to show that the flattening of their stellar distribution depends both on luminosity and on the presence of a nuclear star cluster. Nucleated satellites are thicker at all luminosities compared to their non-nucleated counterparts, and fainter galaxies are systematically thicker as well, regardless of nucleation. Once nucleation is accounted for, we find no evidence that the environment the satellites live in plays a relevant role in setting their 3D structure. We interpret both the presence of stellar nuclei and the associated thicker shapes as the result of preferential early and rapid formation, effectively making these faint nucleated galaxies the first generation of cluster satellites.
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.
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 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.
We study the intrinsic shapes of a sample of over 400 quiescent galaxies in the cores of the Virgo and Fornax clusters with luminosities \(10^{6} \leq L_{g}/L_{\odot} \leq 10^{8}\). Similar to ...satellites of the Local Group and Centaurus A, these faint, low surface brightness cluster galaxies are best described as a family of thick (\(C/A > 0.5\)), oblate-triaxial spheroids. However, the large sample size allows us to show that the flattening of their stellar distributions depends both on luminosity and on the presence of a nuclear star cluster. Nucleated satellites are thicker at all luminosities compared to their non-nucleated counterparts, and fainter galaxies are systematically thicker as well, regardless of nucleation. Once nucleation is accounted for, we find no evidence that the environment the satellites live in plays a relevant role in setting their three-dimensional structure. We interpret both the presence of stellar nuclei and the associated thicker shapes as the result of preferential early and rapid formation, effectively making these faint nucleated galaxies the first generation of cluster satellites.
We present the analysis of 61 nucleated dwarf galaxies in the central regions (\(<R_{\rm vir}/4\)) of the Fornax galaxy cluster. The galaxies and their nuclei are studied as part of the Next ...Generation Fornax Survey (NGFS) using optical imaging obtained with the Dark Energy Camera (DECam) mounted at Blanco/CTIO 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 PSF 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 \(\log({\cal M_*}/M_\odot)\!\simeq\!5.4\) and \(\sim\,6.3\). These two nucleus sub-populations have different stellar population properties, the more massive nuclei are older than \(\sim\!2\) Gyr and have metal-poor stellar populations (\(Z\leq0.02\,Z_\odot\)), while the less massive nuclei are younger than \(\sim\!2\) Gyr with metallicities in the range \(0.02\!<\!Z/Z_\odot\!\leq\!1\). We find that the nucleus mass (\({\cal M}_{\rm nuc}\)) vs. galaxy mass (\({\cal M}_{\rm gal}\)) relation becomes shallower for less massive galaxies starting around \(10^8\,M_\odot\) and the mass ratio \(\eta_n\!=\!{\cal M}_{\rm nuc}/{\cal M}_{\rm gal}\) shows a clear anti-correlation with \({\cal M}_{\rm gal}\) 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 seem to be acting during nucleus growth over cosmic time.
Using the photometric data from the Next Generation Fornax Survey, we find a significant radial alignment signal among the Fornax dwarf galaxies. For the first time, we report that the radial ...alignment signal of nucleated dwarfs is stronger than that of non-nucleated ones at the 2.4 confidence level, and the dwarfs located in the outer region (R > Rvir/3; Rvir is the Fornax virial radius) show a slightly stronger radial alignment signal than those in the inner region (R < Rvir/3) at the 1.5 level. We also find that the significance of the radial alignment signal is independent of the luminosities or sizes of the dwarfs.
We present a photometric study of the dwarf galaxy population in the core region (\(< r_{\rm vir}/4\)) 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-meter Blanco telescope at the Cerro-Tololo Interamerican Observatory. We identify 258 dwarf galaxy candidates with luminosities \(-17 < M_{g'} < -8\) mag, corresponding to typical stellar masses of \(9.5\gtrsim \log{\cal M}_{\star}/M_\odot \gtrsim 5.5\), reaching \(\sim\!3\) mag deeper in point-source luminosity and \(\sim\!4\) mag deeper in surface-brightness sensitivity compared to the classic Fornax Cluster Catalog. Morphological analysis shows that surface-brightness profiles are well represented by single-component Sérsic models with average Sérsic indices of \(\langle n\rangle_{u',g',i'}=(0.78-0.83) \pm 0.02\), and average effective radii of \(\langle r_e\rangle_{u',g',i'}\!=(0.67-0.70) \pm 0.02\) kpc. 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: i) dwarf galaxies assemble mass inside the half-mass radius up to \(\log{\cal M}_{\star}\) ~8.0, ii) isometric mass assembly in the range \(8.0 < \log{\cal M}_{\star}/M_\odot < 10.5\), and iii) massive galaxies assemble stellar mass predominantly in their halos at \(\log{\cal M}_{\star}\) ~10.5 and above.
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