Stellar Velocity Dispersion of the Leo A Dwarf Galaxy

We measure the first stellar velocity dispersion of the Leo A dwarf galaxy, \sigma = 9.3 ± 1.3 km/s. We derive the velocity dispersion from the radial velocities of ten young B supergiants and two HII regions in the central region of Leo A. We estimate a projected mass of 8 ± 2.7 x10^7 solar masses within a radius of 2 arcmin, and a mass to light ratio of at least 20 ± 6 M_sun/L_sun. These results imply Leo A is at least ~80% dark matter by mass.