Kavli Affiliate: Anna Frebel
| First 5 Authors: Anirudh Chiti, Joshua D. Simon, Anna Frebel, Andrew B. Pace, Alexander P. Ji
| Summary:
We present a chemodynamical study of the Grus I ultra-faint dwarf galaxy
(UFD) from medium-resolution ($Rsim11,000$) Magellan/IMACS spectra of its
individual member stars. We identify eight confirmed members of Grus I, based
on their low metallicities and coherent radial velocities, and four candidate
members for which only velocities are derived. In contrast to previous work, we
find that Grus I has a very low mean metallicity of $langle$[Fe/H]$rangle =
-2.62 pm 0.11$ dex, making it one of the most metal-poor UFDs. Grus I has a
systemic radial velocity of $-143.5pm1.2$ km s$^{-1}$ and a velocity
dispersion of $sigma_{text{rv}} = 2.5^{+1.3}_{-0.8}$ km s$^{-1}$ which
results in a dynamical mass of $M_{1/2}(r_h) = 8^{+12}_{-4} times 10^5$
M$_{odot}$ and a mass-to-light ratio of M/L$_V$ = $440^{+650}_{-250}$
M$_odot$/L$_odot$. Our analysis confirms that Grus I is a
dark-matter-dominated UFD (M/L $> 80$ M$_odot$/L$_odot$). However, we do not
resolve a metallicity dispersion ($sigma_{text{[Fe/H]}} < 0.44$ dex). Our
results indicate that Grus I is a fairly typical UFD with parameters that agree
with mass-metallicity and metallicity-luminosity trends for faint galaxies.
This agreement suggests that Grus I has not lost an especially significant
amount of mass from tidal encounters with the Milky Way, in line with its
orbital parameters. Intriguingly, Grus I has among the lowest central density
($rho_{1/2} sim 3.5_{-2.1}^{+5.7} times 10^7$ M$_odot$ kpc$^{-3}$) of the
UFDs that are not known to be tidally disrupting. Models of the formation and
evolution of UFDs will need to explain the diversity of these central
densities, in addition to any diversity in the outer regions of these relic
galaxies.
| Search Query: ArXiv Query: search_query=au:”Anna Frebel”&id_list=&start=0&max_results=10