The star formation history of the Large Magellanic Cloud

Abstract

Deep photometric observations of stars in three fields of the LMC are presented, and these data are interpreted using synthetic CMDs and LFs generated from overshoot models. The field CMDs and LFs with a star formation rate that experienced a large increase (4 +/- 0.5) x 10 exp 9 yr ago is successfully modeled. The precise age of this 'burst' depends sensitively on the characteristics of the models. Classical (i.e., nonovershoot) models yield a burst age about 2 x 10 exp 9 yr younger than the value obtained. An initial mass function with slope of 2.35 (the Salpeter value) and a mean field star metallicity of Fe/H of about -0.7 are consistent with the photometric data and LFs. It is suggested that the star formation rate in the LMC was globally quite low during at least the first half of its lifetime, and that a major event triggered a substantial and relatively sudden increase in the star formation rate throughout the entire LMC which persisted for several 10 exp 9 yr and even up to the present epoch in some parts of that galaxy.