| Abstract | Systemic velocities and distances of 61 Cepheids in three 40' diameter fields in the bar of the SMC have been measured using multiobject fiber-optic spectroscopy with the Anglo-Australian Telescope and IR photometry on the 2.3 m telescope at Siding Spring Observatory. The results of a high velocity resolution H I survey of this region with the Parkes 64 m radio telescope are also presented together with velocity data for other Population I components obtained by other workers. The Cepheid distance measurements confirm previous work that the SMC has a depth of about 20 kpc and the northeastern section of the bar is 10-15 kpc closer than the southern section. There are regions in the three fields where Cepheids cluster in groups of similar radial velocities and distances. These coincide with the groups identified by Maurice and coworkers from their CORAVEL radial velocity measurements of F-M supergiants, which in turn can be identified with particular velocity features of the H I maps. In the first field, southwest of the optical center, there are two such groups, which, when plotted on the H I velocity map, show a good correspondence with the regions of strong H I emission and mimic the velocity gradient of the gas. When combined with the interstellar absorption line data for OB stars, it appears that the Population I stars can be associated with the H I emission, and the low-velocity components are nearer than the high-velocity components. This velocity-distance correlation is also supported by the Cepheids which lie outside the zones of uniform radial velocity in the other two fields. This correlation agrees with the model of Murai and Fujimoto (1980), which predicts that the SMC collided with the LMC some 2 x 10^8^ years ago. The general picture of the structure and kinematics of the SMC supports the view that the SMC is a galaxy disrupted by this collision. |
