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تسجيل مستخدم جديدDwarf galaxies in the MATLAS survey: Hubble Space Telescope observations of the globular cluster system in the ultra-diffuse galaxy MATLAS-2019
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Ultra-diffuse galaxies (UDGs) are very low-surface brightness galaxies with large effective radii. Spectroscopic measurements of a few UDGs have revealed a low dark matter content, based on the internal motion of stars or globular clusters (GCs). This is in contrast to the large number of GCs found for these systems, from which it would be expected to correspond to a large dark matter halo mass. Here we present Hubble Space Telescope Advanced Camera Survey observations for the UDG MATLAS-2019 in the NGC5846 group of galaxies. Using images in the $F606W$ and $F814W$ filters, we trace the GC population two magnitudes below the peak of the GC luminosity function. Employing Bayesian considerations, we find a total of 37$pm$5 GCs associated with the dwarf, which yields a large GC specific frequency of $S_N=84pm 12$. Due to the superior image quality of the HST, we are able to resolve the GCs and measure their sizes, which are consistent with the sizes of GCs from Local Group galaxies. Using the linear relation between the total mass of a galaxy and the total mass of GCs we derive a halo mass of $1.3pm0.2times10^{11}$ M$_odot$, corresponding to a mass-to-light ratio of over 1000. This suggests that either this UDG has an overly massive dark matter halo for its stellar mass, compared to other dwarfs -- though not as massive as the Milky Way -- or that the linear relation between the number of GCs and the dark matter halo mass breaks down for UDGs like MATLAS-2019. The high abundance of GCs, together with the small uncertainties, make MATLAS-2019 one of the most extreme UDGs, which likely sets an upper limit of the number of GCs for such objects.
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The MATLAS deep imaging survey has uncovered a plethora of dwarf galaxies in the low density environment it has mapped. A fraction of them are unusually extended and have a low-surface brightness. Among these so-called ultra-diffuse galaxies, a few s
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We present a photometric study of the dwarf galaxy population in the low to moderate density environments of the MATLAS (Mass Assembly of early-Type gaLAxies with their fine Structures) deep imaging survey. The sample consists of 2210 dwarfs, includi
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ted in galaxies with such low stellar density and mass. We have carried out a comprehensive study of GCs in both UDGs and classical dwarf galaxies at comparable stellar masses using HST observations of the Coma cluster. We present new imaging for 33 Dragonfly UDGs with the largest effective radii ($>2$ kpc), and additionally include 15 UDGs and 54 classical dwarf galaxies from the HST/ACS Coma Treasury Survey and the literature. Out of a total of 48 UDGs, 27 have statistically significant GC systems, and 11 have candidate nuclear star clusters. The GC specific frequency ($S_N$) varies dramatically, with the mean $S_N$ being higher for UDGs than for classical dwarfs. At constant stellar mass, galaxies with larger sizes (or lower surface brightnesses) have higher $S_N$, with the trend being stronger at higher stellar mass. At lower stellar masses, UDGs tend to have higher $S_N$ when closer to the center of the cluster, i.e., in denser environments. The fraction of UDGs with a nuclear star cluster also depends on environment, varying from $sim!40$% in the cluster core, where it is slightly lower than the nucleation fraction of classical dwarfs, to $lesssim20%$ in the outskirts. Collectively, we observe an unmistakable diversity in the abundance of GCs, and this may point to multiple formation routes.
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