The radial velocity, velocity dispersion, and mass-to-light ratio of the Sculptor dwarf galaxy

Radial velocities for 16 K giants in the Sculptor dwarf spheroidal galaxy are presented. The velocities have been determined via cross-correlation techniques from spectra obtained at the calcium infrared triplet. They have a single-observation accuracy of 4.7 km/s. The mean velocity of the Sculptor stars is +107.4±2.0 km/s, a value that supports the adoption of a large mass for the Galaxy. The one-dimensional velocity dispersion of this sample is 6.3 (+1.1, -1.3) km/s, a value which, when combined with a new estimate of the core radius of the galaxy and the observed central surface brightness, yields a visual mass-to-light ratio of 6.0 in solar units. This value is more than twice current estimates of global mass-to-light ratios of globular clusters, and thus, if interpreted literally, indicates that Sculptor contains a substantial amount of additional mass not found in globular clusters.