The Star Formation History of the Large Magellanic Cloud

Abstract

Using WFPC2 on board the Hubble Space Telescope, we have created deep color-magnitude diagrams in the V and I passbands for approximately 10⁵ stars in a field at the center of the LMC bar and another in the disk. The main-sequence luminosity functions (LFs) from 19<=V<=23.5, the red clump and horizontal branch morphologies, and the differential Hess diagram of the two fields all strongly imply that the disk and bar have significantly different star formation histories (SFHs). The disk's SFH has been relatively smooth and continuous over the last ~15 Gyr, while the bar's SFH was dominated by star formation episodes at intermediate ages. Comparison of the LF against predictions based on Padova theoretical stellar evolution models and an assumed age-metallicity relationship allows us to identify the dominant stellar populations in the bar with episodes of star formation that occurred from 4 to 6 and 1 to 2 Gyr ago. These events accounted for ~25% and ~15%, respectively, of its stellar mass. The disk field may share a mild enhancement in SF for the younger episode, and thus we identify the 4 to 6 Gyr episode with the formation of the LMC bar. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract 5-26555.