Magellan/IMACS Spectroscopy of Grus I: A Low Metallicity Ultra-faint Dwarf Galaxy*
Abstract

We present a chemodynamical study of the Grus I ultra-faint dwarf galaxy (UFD) from medium-resolution (R∼ 11,000) 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 〈[Fe/H]〉 = −2.62 ± 0.11 dex, making it one of the most metal-poor UFDs. Grus I has a systemic radial velocity of −143.5 ± 1.2 km s−1and a velocity dispersion of$σrv=2.5−0.8+1.3$km s−1, which results in a dynamical mass of$M1/2(rh)=8−4+12×105$Mand a mass-to-light ratio ofM/LV=$440−250+650$M/L. Under the assumption of dynamical equilibrium, our analysis confirms that Grus I is a dark-matter-dominated UFD (M/L> 80M/L). However, we do not resolve a metallicity dispersion (σ[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 more »

Authors:
; ; ; ; ;
Publication Date:
NSF-PAR ID:
10378528
Journal Name:
The Astrophysical Journal
Volume:
939
Issue:
1
Page Range or eLocation-ID:
Article No. 41
ISSN:
0004-637X
Publisher:
DOI PREFIX: 10.3847
National Science Foundation
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