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Context. Studies of low surface brightness (LSB) galaxies in nearby clusters have revealed a sub-population of extremely diffuse galaxies with central surface brightness of µ 0,g > 24 mag arcsec −2 , total luminosity M g fainter than -16 mag and effective radius between 1.5 kpc < R e < 10 kpc. The origin of these Ultra Diffuse Galaxies (UDGs) is still unclear, although several theories have been suggested. As the UDGs overlap with the dwarf-sized galaxies in their luminosities, it is important to compare their properties in the same environment. If a continuum is found between the properties of UDGs and the rest of the LSB population, it would be consistent with the idea that they have a common origin. Aims. Our aim is to exploit the deep g', r' and i'-band images of the Fornax Deep Survey (FDS), in order to identify LSB galaxies in an area of 4 deg 2 in the center of the Fornax cluster. The identified galaxies are divided into UDGs and dwarf-sized LSB galaxies, and their properties are compared. Methods. We identify visually all extended structures having r'-band central surface brightness of µ 0,r > 23 mag arcsec −2 . We classify the objects based on their appearance into galaxies and tidal structures, and perform 2D Sérsic model fitting with GALFIT to measure the properties of those classified as galaxies. We analyze their radial distribution and orientations with respect of the cluster center, and with respect to the other galaxies in our sample. We also study their colors and compare the LSB galaxies in Fornax with those in other environments. Results. Our final sample complete in the parameter space of the previously known UDGs, consists of 205 galaxies of which 196 are LSB dwarfs (with R e < 1.5kpc) and 9 are UDGs (R e > 1.5 kpc). We show that the UDGs have (1) g'-r' colors similar to those of LSB dwarfs of the same luminosity. (2) The largest UDGs (R e >3kpc) in our sample appear different from the other LSB galaxies, in that they are significantly more elongated and extended, whereas (3) the smaller UDGs differ from the LSB dwarfs only by having slightly larger effective radii. (4) We do not find clear differences between the structural parameters of the UDGs in our sample and those of UDGs in other galaxy environments. (5) We find that the dwarf LSB galaxies in our sample are less concentrated in the cluster center than the galaxies with higher surface brightness, and that their number density drops within 180 kpc from the cluster center. We also compare the LSB dwarfs in Fornax with the LSB dwarfs in the Centaurus group, where data of similar quality to ours is available. (6) We find the smallest LSB dwarfs to have similar colors, sizes and Sérsic profiles regardless of their environment. However, in the Centaurus group the colors become bluer with increasing galaxy magnitudes, an effect which is probably due to smaller mass and hence weaker environmental influence of the Centaurus group. Conclusions. Our findings are consistent with the small UDGs forming the tail of a continuous distribution...
Context. Studies of low surface brightness (LSB) galaxies in nearby clusters have revealed a sub-population of extremely diffuse galaxies with central surface brightness of µ 0,g > 24 mag arcsec −2 , total luminosity M g fainter than -16 mag and effective radius between 1.5 kpc < R e < 10 kpc. The origin of these Ultra Diffuse Galaxies (UDGs) is still unclear, although several theories have been suggested. As the UDGs overlap with the dwarf-sized galaxies in their luminosities, it is important to compare their properties in the same environment. If a continuum is found between the properties of UDGs and the rest of the LSB population, it would be consistent with the idea that they have a common origin. Aims. Our aim is to exploit the deep g', r' and i'-band images of the Fornax Deep Survey (FDS), in order to identify LSB galaxies in an area of 4 deg 2 in the center of the Fornax cluster. The identified galaxies are divided into UDGs and dwarf-sized LSB galaxies, and their properties are compared. Methods. We identify visually all extended structures having r'-band central surface brightness of µ 0,r > 23 mag arcsec −2 . We classify the objects based on their appearance into galaxies and tidal structures, and perform 2D Sérsic model fitting with GALFIT to measure the properties of those classified as galaxies. We analyze their radial distribution and orientations with respect of the cluster center, and with respect to the other galaxies in our sample. We also study their colors and compare the LSB galaxies in Fornax with those in other environments. Results. Our final sample complete in the parameter space of the previously known UDGs, consists of 205 galaxies of which 196 are LSB dwarfs (with R e < 1.5kpc) and 9 are UDGs (R e > 1.5 kpc). We show that the UDGs have (1) g'-r' colors similar to those of LSB dwarfs of the same luminosity. (2) The largest UDGs (R e >3kpc) in our sample appear different from the other LSB galaxies, in that they are significantly more elongated and extended, whereas (3) the smaller UDGs differ from the LSB dwarfs only by having slightly larger effective radii. (4) We do not find clear differences between the structural parameters of the UDGs in our sample and those of UDGs in other galaxy environments. (5) We find that the dwarf LSB galaxies in our sample are less concentrated in the cluster center than the galaxies with higher surface brightness, and that their number density drops within 180 kpc from the cluster center. We also compare the LSB dwarfs in Fornax with the LSB dwarfs in the Centaurus group, where data of similar quality to ours is available. (6) We find the smallest LSB dwarfs to have similar colors, sizes and Sérsic profiles regardless of their environment. However, in the Centaurus group the colors become bluer with increasing galaxy magnitudes, an effect which is probably due to smaller mass and hence weaker environmental influence of the Centaurus group. Conclusions. Our findings are consistent with the small UDGs forming the tail of a continuous distribution...
Context. The Fornax Deep Survey (FDS), an imaging survey in the u , g , r , and i -bands, has a supreme resolution and image depth compared to the previous spatially complete Fornax Cluster Catalog (FCC). Our new data allows us to study the galaxies down to r -band magnitude m r ≈ 21 mag (M r ≈ −10.5 mag), which opens a new parameter regime to investigate the evolution of dwarf galaxies in the cluster environment. After the Virgo cluster, Fornax is the second nearest galaxy cluster to us, and with its different mass and evolutionary state, it provides a valuable comparison that makes it possible to understand the various evolutionary effects on galaxies and galaxy clusters. These data provide an important legacy dataset to study the Fornax cluster. Aims. We aim to present the Fornax Deep Survey (FDS) dwarf galaxy catalog, focusing on explaining the data reduction and calibrations, assessing the quality of the data, and describing the methods used for defining the cluster memberships and first order morphological classifications for the catalog objects. We also describe the main scientific questions that will be addressed based on the catalog. This catalog will also be invaluable for future follow-up studies of the Fornax cluster dwarf galaxies. Methods. As a first step we used the SExtractor fine-tuned for dwarf galaxy detection, to find galaxies from the FDS data, covering a 26 deg 2 area of the main cluster up to its virial radius, and the area around the Fornax A substructure. We made 2D-decompositions of the identified galaxies using GALFIT, measure the aperture colors, and the basic morphological parameters like concentration and residual flux fraction. We used color-magnitude, luminosity-radius and luminosity-concentration relations to separate the cluster galaxies from the background galaxies. We then divided the cluster galaxies into early-and late-type galaxies according to their morphology and gave first order morphological classifications using a combination of visual and parametric classifications. Results. Our final catalog includes 14 095 galaxies. We classify 590 galaxies as being likely Fornax cluster galaxies, of which 564 are dwarfs (M r > −18.5 mag) consisting our Fornax dwarf catalog. Of the cluster dwarfs we classify 470 as early-types, and 94 as late-type galaxies. Our final catalog reaches its 50% completeness limit at magnitude M r = −10.5 mag and surface brightness µ e,r = 26 mag arcsec −2 , which is approximately three magnitudes deeper than the FCC. Based on previous works and comparison with a spectroscopically confirmed subsample, we estimate that our final Fornax dwarf galaxy catalog has 10% contamination from the background objects.The catalogs are only at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A165Article published by EDP Sciences A165, page 1 of 31 A&A 620, A165 (2018)
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