Dwarf Galaxies in the MATLAS Survey: Hubble Space Telescope Observations of the Globular Cluster System in the Ultra-diffuse Galaxy MATLAS-2019

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 HST+ACS observations for the UDG MATLAS-2019 in the NGC 5846 group. Using the F606W and F814W filters, we trace the GC population two magnitudes below the peak of the GC luminosity function (GCLF). Employing Bayesian considerations, we identify 26 ± 6 GCs associated with the dwarf, yielding a large specific frequency of S N = 58 ± 14. We use the turnover of the GCLF to derive a distance of 21 ± 2 Mpc, which is consistent with the NGC 5846 group of galaxies. 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 around Local Group galaxies. Using the linear relation between the total mass of galaxies and of GCs, we derive a halo mass of 0.9 ± 0.2 × 1011 M ⊙ (M ⊙/L ⊙ > 1000). 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 UDGs.

Boson dark matter halos with a dominant noncondensed component

We consider galaxy halos formed by dark matter bosons with mass in the range of about a few tens or hundreds eV. A major part of the particles is in a noncondensed state and described under the Thomas-Fermi approach. Derived equations are solved numerically to find the halo density profile. The noncondensed state is supported in the entire halo except compact gravitationally bounded Bose-Einstein condensates. Although the size of these compact objects, also known as Bose stars, depends on interactions between the particles, its upper limit is only about 100 astronomical units. The Bose stars collect the condensed bosons providing a density cusp avoidance in the halo as well as a natural mechanism to prevent overproduction of small halos. Clusters of the Bose stars can also contribute to the halo density profile. The model is analyzed by confronting its predictions with observations of galaxy rotation curves. We employ 22 low surface brightness galaxies and obtain that the model is consistent with the observational data when the particle mass is in the range above about 50 eV and the best fit corresponds to the mass m = 86 eV. This mass is appropriate for relic dark matter bosons, which decouple just after QCD phase transition.

Star Formation Rate of the Low Redshift Dwarf Galaxies J080947.50+213717.2 and J151839.94+220514.4

We performed a spectroscopic analysis of two low redshift dwarf galaxies, SDSSJ080947.50+213717.2, and SDSSJ151839.94+220514.4 selected from a catalogue of Paudel et al. 2018. The strong emission lines of the SDSS spectra of both galaxies were studied and the elements responsible were identified for those characteristic lines. The line ratio between Hα and Hβ (Hα/ Hβ) for the galaxies SDSSJ080947.50+213717.2 and SDSSJ151839.94+220514.4 was found to be 2.77 and 2.75, respectively, suggesting these are nearly dust free and star forming galaxies.. The star formation rate of the galaxies SDSSJ080947.50+213717.2 and SDSSJ151839.94+220514.4 was found to be 0.0232 M☉yr-1 and 0.05221 M☉yr-1, respectively. The ratio between NII and Hα was used to calculate the emission line metallicity, which was found to be 8.13 dex and 8.46 dex for the galaxies SDSSJ080947.50+213717.2 and SDSSJ151839.94+220514.4, respectively. From the comparison of our findings with the previous studies, slightly lower star formation rate than normal galaxies were noticed. The metallicity value for both of the galaxies were positioned in the group of low-surface-brightness galaxies of Bargvell's dwarfs..