Magellanic Cloud Periphery Carbon Stars. IV. The SMC

Abstract

The kinematics of 150 carbon stars observed at moderate dispersion on the periphery of the Small Magellanic Cloud are compared with the motions of neutral hydrogen and early-type stars in the intercloud region. The distribution of radial velocities implies a configuration of these stars as a sheet inclined at 73° ± 4° to the plane of the sky. The near side, to the south, is dominated by a stellar component; to the north, the far side contains fewer carbon stars and is dominated by the neutral gas. The upper velocity envelope of the stars is closely the same as that of the gas. This configuration is shown to be consistent with the known extension of the SMC along the line of sight and is attributed to a tidally induced disruption of the SMC that originated in a close encounter with the LMC some 0.3 to 0.4 Gyr ago. The dearth of gas on the near side of the sheet is attributed to ablation processes akin to those inferred in 1996 by Weiner & Williams to collisional excitation of the leading edges of Magellanic Stream clouds. Comparison with the 1989 kinematic data of Hardy, Suntzeff, & Azzopardi and Maurice, Martin, & Bouchet and the 1986 and 1988 data of Mathewson et al. leaves little doubt that forces other than gravity play a role in the dynamics of the H I.