Constraints on the star formation history of the Large Magellanic Cloud

Abstract

We present the analysis of deep colour-magnitude diagrams (CMDs) of 6 stellar fields in the LMC. The data were obtained using HST/WFPC2 in the I and V filters, reaching V=26.5. We discuss and apply a method of correcting CMDs for photometric incompleteness. A method to generate artificial CMDs based on a model star formation history is also developed. This method incorporates photometric error effects, unresolved binaries, reddening and allows use of different forms of the initial mass function and of the SFH itself. We use the Partial Models Method, as presented by Gallart and others, for CMD modelling, and include control experiments to prove its validity in a search for constraints on the Large Magellanic Cloud star formation history in different regions. Reliable star formation histories for each field are recovered by this method. In all fields, a gap in star formation with t=700 Myrs is observed. Field-to-field variations have also been observed. The two fields near the LMC bar present some significant star forming events, having formed both young (t < 1Gyr) and old (t > 10 Gyrs) stars, with a clear gap from 3-6 Gyrs. Two other fields display quite similar SFHs, with increased star formation having taken place at t=2-3 Gyrs and 6 < t < 10 Gyrs. The remaining two fields present star formation histories closer to uniform, with no clear event of enhanced star formation.