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 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.
We report the discovery of 271 previously undetected dwarf galaxies in the outer Fornax cluster regions at radii \(r_{\rm vir}/4<\!r\!<r_{\rm vir}/2\) 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 are 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 \(-18.80\le\,M_{i'}\le\,-8.78\) with effective radii \(r_{{\rm eff},i'}\,=\,0.18-2.22\) kpc and an average Sersic index \(\langle n\rangle_{i'}\,=\,0.81\). Non-nucleated dwarfs are found to be fainter and smaller by \(\Delta\langle M_{i'}\rangle\!=\!2.25\) mag and \(\Delta\langle r_{{\rm eff},i'}\rangle\!=\!0.4\) kpc than the nucleated dwarfs. We demonstrate a significant clustering of dwarf galaxies on scales \(\lesssim\!100\) kpc, and projected surface number density profile estimates, \(\Sigma_N(r)\), show a concentration of dwarfs in the Fornax core region within \(r\!\sim\!350\) kpc. \(\Sigma_N(r)\) has a flat distribution up to \(\sim\!350\) kpc, beyond which it declines for the non-nucleated dwarfs. The nucleated dwarfs have a steeper \(\Sigma_N(r)\) distribution, being more concentrated towards NGC 1399 and 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 present the results of a wide spectroscopic survey aimed at detecting extragalactic globular clusters (GCs) in the core of the Fornax cluster. About 4500 low resolution spectra (from 4800 to 10000 ...\AA ) were observed in 25 VLT/VIMOS masks covering the central 1 deg\(^{2}\) around the dominant galaxy NGC 1399 corresponding to \(\sim\)175 kpc galactocentric radius. We describe the methodology used for data reduction and data analysis. We found a total of 387 unique physical objects (372 GCs and 15 ultra compact dwarfs) in the field covered by our observations. Most of these objects are associated with NGC 1399, with only 10% likely belonging to other giant galaxies. The new VIMOS dataset is complementary to the many GC catalogues already present in the literature and it brings the total number of tracer particles around NGC 1399 to more than 1130 objects. With this comprehensive radial velocity sample we have found that the velocity dispersion of the GC population (equally for red and blue GC populations) shows a relatively sharp increase from low velocity dispersion (\(\sim250\)-\(350\) kms\(^{-1}\)) to high velocity dispersion (\(\sim300\)-\(400\) kms\(^{-1}\)) at projected radius of \(\approx10\) arcmin (\(\sim60\) kpc) from the galaxy centre. This suggests that at a projected radius of \(\approx60\) kpc both blue and red GC populations begin to be governed by the dominating Fornax cluster potential, rather than by the central NGC 1399 galaxy potential. This kinematic evidence corroborates similar results found using surface brightness analysis and planetary nebulae kinematics.
Polar ring galaxies (PRGs) are composed of two kinematically distinct and nearly orthogonal components, a host galaxy (HG) and a polar ring/disk (PR). The HG usually contains an older stellar ...population than the PR. The suggested formation channel of PRGs is still poorly constrained. Suggested options are merger, gas accretion, tidal interaction, or a combination of both. To constrain the formation scenario of PRGs, we study the compact stellar systems (CSSs) in two PRGs at different evolutionary stages: NGC?4650A with well-defined PR, and NGC?3808?B, which is in the process of PR formation. We use archival HST/WFPC2 imaging in the F450W, F555W, or F606W and F814W filters. Extensive completeness tests, PSF-fitting techniques, and color selection criteria are used to select cluster candidates. The spatial distribution, masses, and peak star formation epoch of the clusters in NGC?3808 suggest for a tidally triggered star formation. Incompleteness at old ages prevents us from probing the SFR at earlier epochs of NGC?4650?A, where we observe the fading tail of CSS formation.
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
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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.)
Context. Polar ring galaxies (PRGs) are composed of two kinematically distinct and nearly orthogonal components, a host galaxy (HG) and a polar ring/disk (PR). The HG usually contains an older ...stellar population than the PR. The suggested formation channel of PRGs is still poorly constrained. Suggested options are merger, gas accretion, tidal interaction, or a combination of both. Aims. To constrain the formation scenario of PRGs, we study the compact stellar systems (CSSs) in two PRGs at different evolutionary stages: NGC 4650A with well-defined PR, and NGC 3808 B, which is in the process of PR formation. Methods. We use archival HST/WFPC2 imaging in the F450W, F555W, or F606W and F814W filters. Extensive completeness tests, PSF-fitting techniques, and color selection criteria are used to select cluster candidates. Photometric analysis of the CSSs was performed to determine their ages and masses using stellar population models at a fixed metallicity. Results. Both PRGs contain young CSSs (<1 Gyr) with masses of up to 5 × 106M⊙, mostly located in the PR and along the tidal debris. The most massive CSSs may be progenitors of metal-rich globular clusters or ultra compact dwarf (UCD) galaxies. We identify one such young UCD candidate, NGC 3808 B-8, and measure its size of reff = 25.23+1.43-2.01 pc. We reconstruct the star formation history of the two PRGs and find strong peaks in the star formation rate (SFR, ≃200 M⊙/yr) in NGC 3808 B, while NGC 4650 A shows milder (declining) star formation (SFR< 10 M⊙/yr). This difference may support different evolutionary paths between these PRGs. Conclusions. The spatial distribution, masses, and peak star formation epoch of the clusters in NGC 3808 suggest for a tidally triggered star formation. Incompleteness at old ages prevents us from probing the SFR at earlier epochs of NGC 4650 A, where we observe the fading tail of CSS formation. This also impedes us from testing the formation scenarios of this PRG.
We present multiobject spectroscopic observations of 23 globular cluster candidates (GCCs) in the prototypical megamaser galaxy NGC 4258, carried out with the Optical System for Imaging and ...low-Intermediate-Resolution Integrated Spectroscopy instrument at the 10.4 m Gran Telescopio Canarias. The candidates have been selected based on the (u* − i′) versus (i′ − Ks) diagram, in the first application of the u*i′Ks method to a spiral galaxy. In the spectroscopy presented here, 70% of the candidates are confirmed as globular clusters (GCs). Our results validate the efficiency of the u*i′Ks method in the sparser GC systems of spirals, and given the downward correction to the total number of GCs, the agreement of the galaxy with the correlations between black hole mass and the total number and mass of GCs is actually improved. We find that the GCs, mostly metal-poor, corotate with the H i disk, even at large galactocentric distances.
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