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 \langle v _ { r } \rangle = -29.1 \pm 1.3 km s ^ { -1 } , in agreement with the previous radio measurements of H i 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 ^ { -1 } on any rotation in the photometric disk-like feature .
The velocity dispersion is \sigma _ { v } = 9.4 \pm 1.0 km s ^ { -1 } , from which we inferred a mass of M _ { 1 / 2 } = ( 2.1 \pm 0.2 ) \times 10 ^ { 7 } ~ { } M _ { \sun } and a mass-to-light ratio of ( M / L _ { V } ) _ { 1 / 2 } = 5.2 \pm 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 , \langle { [ Fe / H ] } \rangle = -1.58 \pm 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 .