Spectroscopic Survey of Red Giants in the Small Magellanic Cloud. I. Kinematics

Abstract

We present a spectroscopic survey of 2046 red giant stars, distributed over the central 4 kpc×2 kpc of the Small Magellanic Cloud (SMC). After fitting and removing a small velocity gradient across the SMC (8.3 km s -1 deg -1 oriented at 23.4d east of north), we measure an rms velocity scatter of 27.5+/-0.5 km s -1. The line-of-sight velocity distribution is well-characterized by a Gaussian, and the velocity dispersion profile is nearly constant as a function of radius. We find no kinematic evidence of tidal disturbances. Without a high-precision measurement of the SMC's proper motion, it is not possible to constrain its true rotation speed from our measured radial velocity gradient. However, even with conservative assumptions, we find that v 9 M solar and a less well-constrained mass within 3 kpc of between 2.7 and 5.1×10 9 M solar. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.