Low mass pre-main sequence stars in the Large Magellanic Cloud - II. HST-WFPC2 observations of two fields in the 30 Doradus region

As a part of an ongoing effort to characterise the young stellar populations in the Large Magellanic Cloud, we present HST-WFPC2 broad and narrow band imaging of two fields with recent star formation activity in the Tarantula region. A population of objects with H alpha and/or Balmer continuum excess was identified. On account of the intense Ha emission (equivalent widths up to several tens of angstrom), its correlation with the Balmer continuum excess and the stars' location on the HR diagram, we interpret them as low mass (similar to 1- 2 M-circle dot) Pre-Main Sequence stars. In this framework, the data show that coeval high and low mass stars have significantly different spatial distributions, implying that star formation processes for different ranges of stellar masses are rather different and/or require different initial conditions. We find that the overall slope of the mass function of the young population is somewhat steeper than the classical Salpeter value and that the star formation density of this young component is 0.2-0.4 M-circle dot yr(-1) kpc(-2), i.e. intermediate between the value for an active spiral disk and that of a starburst region. The uncertainties associated with the determination of the slope of the mass function and the star formation density are thoroughly discussed.