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Register a new userThe Next Generation Fornax Survey (NGFS): VII. A MUSE view of the nuclear star clusters in Fornax dwarf galaxies
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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 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 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, while 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 which 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.
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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 2.4$sigma$ confidence level, and the dwarfs located in the outer region ($R>R_{rm{vir}}/3$; $R_{rm{vir}}$ is the Fornax virial radius) show slightly stronger radial alignment signal than those in the inner region ($R<R_{rm{vir}}/3$) at $1.5sigma$ level. We also find that the significance of 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 $ugi$ 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 $9.5gtrsim log{cal M}_{star}/M_odot gtrsim 5.5$, 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 Sersic models with average Sersic indices of $langle nrangle_{u,g,i}=(0.78-0.83) pm 0.02$, and average effective radii of $langle r_erangle_{u,g,i}!=(0.67-0.70) pm 0.02$ 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.
We report the detection of a pair of dwarf galaxies at $z!=!0.30$ which may be in the early stages of an interaction. Both galaxies have stellar masses of $<10^{9}M_odot$, and display a projected separation of $sim!29$kpc and a physical separation of $sim!240$kpc. Evidence of ongoing star formation has been found in both galaxies, with neither one showing an enhanced star-formation rate that would be expected if they were already interacting. One galaxy displays a disturbed morphology but shows ordered gas rotation, which may reflect a previous minor merger event in the recent history of that system. The nearest spectroscopically confirmed neighbour lies at a distance of 38Mpc. These results indicate that these dwarf galaxies have no neighbouring massive galaxies, however with the data available we have been unable to determine whether these galaxies are isolated in the field or belong to a group of low-mass galaxies. As a detection of a rare dwarf-dwarf pair beyond the Local Universe, this system provides an uncommon opportunity to explore the properties of galaxy groups in the low-galaxy mass regime as a function of redshift.
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 DECam wide-field camera mounted on the 4-meter Blanco telescope at the Cerro Tololo Interamerican Observatory as part of the {it Next Generation Fornax Survey} (NGFS). The new dwarf galaxies have quasi-exponential light profiles, effective radii $0.1!<!r_e!<!2.8$ kpc and average effective surface brightness values $22.0!<!mu_i!<!28.0$ 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 $M_i!=!-8.0$,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 $M_i!simeq!-15.0$ mag to $0%$ at luminosities fainter than $M_i!simeq!-10.0$ mag. The two-point correlation function analysis of the NGFS dwarf sample shows an excess on length scales below $sim!100$ kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core.
The Fornax Deep Survey Dwarf galaxy Catalog (FDSDC) includes 564 dwarf galaxies in the Fornax cluster and the in-falling Fornax A subgroup. We use the FDSDC galaxies for statistical analysis of the structural and stellar population differences in the range of galactic environments within the Fornax cluster. We present the standard scaling relations for the dwarfs and analyze trends as a function of cluster-centric radius. We find a different behavior for the bright dwarfs (-18.5 mag < M$_r$ < -16 mag) as compared to the fainter ones (M$_r$ > -16 mag): While considering galaxies in the same magnitude-bins, we find that, while for fainter dwarfs the g-r color is redder for lower surface brightness objects (as expected from fading stellar populations), for brighter dwarfs the color is redder for the higher surface brightness and higher Sersic n objects. The trend of the bright dwarfs might be explained by those galaxies being affected by harassment and by slower quenching of star formation in their inner parts. As the fraction of early-type dwarfs with respect to late-types increases toward the central parts of the cluster, the color-surface brightness trends are also manifested in the cluster-centric trends, confirming that it is indeed the environment that changes the galaxies. We also estimate the strengths of the ram-pressure stripping, tidal disruption, and harassment in the Fornax cluster, and find that our observations are consistent with the theoretically expected ranges of galaxy properties where each of those mechanisms dominate. We furthermore find that the luminosity function, color-magnitude relation, and axis-ratio distribution of the dwarfs in the center of the Fornax cluster are similar to those in the center of the Virgo cluster.
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