The star formation history of the Small Magellanic Cloud

We present the spatially resolved star formation and chemical enrichment history of the Small Magellanic Cloud (SMC) across the entire central 4degrees x 4.degrees5 area of the main body, based on UBVI photometry from our Magellanic Clouds Photometric Survey. We find that ( 1) approximately 50% of the stars that ever formed in the SMC formed prior to 8.4 Gyr ago ( z > 1.2 for WMAP cosmology); (2) the SMC formed relatively few stars between 8.4 and 3 Gyr ago; ( 3) there was a rise in the mean star formation rate during the most recent 3 Gyr punctuated by bursts'' at ages of 2.5, 0.4, and 0.06 Gyr; ( 4) the bursts at 2.5 and 0.4 Gyr are temporally coincident with past perigalactic passages of the SMC with the Milky Way; ( 5) there is preliminary evidence for a large-scale annular structure in the 2.5 Gyr burst; and ( 6) the chemical enrichment history derived from our analysis is in agreement with the age-metallicity relation of the SMC's star clusters. Consistent interpretation of the data required an ad hoc correction of 0.1 - 0.2 mag to the B - V colors of 25% of the stars; the cause of this anomaly is unknown, but we show that it does not strongly influence our results.