The Morphologies of the Small Magellanic Cloud

We compare the distribution of stars of different spectral types, and hence mean age, within the central SMC and find that the asymmetric structures are almost exclusively composed of young main-sequence stars. Because of the relative lack of older stars in these features and the extremely regular distribution of red giant and clump stars in the SMC central body, we conclude that tides alone are not responsible for the irregular appearance of the central SMC. The dominant physical mechanism in determining the current-day appearance of the SMC must be star formation triggered by a hydrodynamic interaction between gaseous components. These results extend the results of population studies (see Gardiner & Hatzidimitriou) inward in radius and also confirm the suggestion of the spheroidal nature of the central SMC based on kinematic arguments (Dopita et al.; Hardy, Suntzeff, & Azzopardi). Finally, we find no evidence in the underlying older stellar population for a "bar" or "outer arm," again supporting our classification of the central SMC as a spheroidal body with highly irregular recent star formation.