Past and Present Star Formation in the SMC: NGC 346 and its Neighborhood

In the quest of understanding how star formation occurs and propagates in thelow metallicity environment of the Small Magellanic Cloud (SMC), we acquireddeep F555W (~V), and F814W (~I) HST/ACS images of the young and massive starforming region NGC 346. These images and their photometric analysis provide uswith a snapshot of the star formation history of the region. We find evidencefor star formation extending from ~10 Gyr in the past until ~150 Myr in thefield of the SMC. The youngest stellar population (~3 +/- 1 Myr) is associatedwith the NGC 346 cluster. It includes a rich component of low mass pre-mainsequence stars mainly concentrated in a number of sub-clusters, spatially co-located with CO clumps previously detected by Rubio et al. (2000). Within ouranalysis uncertainties, these sub-clusters appear coeval with each other. Themost massive stars appear concentrated in the central sub-clusters, indicatingpossible mass segregation. A number of embedded clusters are also observed.This finding, combined with the overall wealth of dust and gas, could implythat star formation is still active. An intermediate age star cluster, BS90,formed ~4.3 +/-0.1 Gyr ago, is also present in the region. Thus, this region ofthe SMC has supported star formation with varying levels of intensity over muchof the cosmic time.Comment: 38 pages, 13 figures, 3 tables; AJ accepte