The Dynamics and Metallicity Distribution of the Distant Dwarf Galaxy
  VV124
  VV124 (UGC 4879) is an isolated, dwarf irregular/dwarf spheroidal (dIrr/dSph)
transition-type galaxy at a distance of 1.36 Mpc. Previous low-resolution
spectroscopy yielded inconsistent radial velocities for different components of
the galaxy, and photometry hinted at the presence of a stellar disk. In order
to quantify the stellar dynamics, we observed individual red giants in VV124
with the Keck/DEIMOS spectrograph. We validated members based on their
positions in the color-magnitude diagram, radial velocities, and spectral
features. Our sample contains 67 members. The average radial velocity is <v_r>
= -29.1 +/- 1.3 km/s, in agreement with the previous radio measurements of HI
gas. The velocity distribution is Gaussian, indicating that VV124 is supported
primarily by velocity dispersion inside a radius of 1.5 kpc. Outside that
radius, our measurements provide only an upper limit of 8.6 km/s on any
rotation in the photometric disk-like feature. The velocity dispersion is
sigma_v = 9.4 +/- 1.0 km/s, from which we inferred a mass of M_1/2 = (2.1 +/-
0.2) x 10^7 M_sun and a mass-to-light ratio of (M/L_V)_1/2 = 5.2 +/- 1.1
M_sun/L_sun, both measured within the half-light radius. Thus, VV124 contains
dark matter. We also measured the metallicity distribution from neutral iron
lines. The average metallicity, <[Fe/H]> = -1.58 +/- 0.06, is consistent with
the mass-metallicity relation defined by dwarf spheroidal galaxies. The
dynamics and metallicity distribution of VV124 appear similar to dSphs of
similar stellar mass.
