The Initial Mass Function toward the Low-Mass End in the Large Magellanic Cloud with Hubble Space Telescope WFPC2 Observations

Abstract

We present V- and I-equivalent Hubble Space Telescope (HST) WFPC2 photometry of two areas in the Large Magellanic Cloud: the southern part of the stellar association LH 52, located on the western edge of the supershell LMC 4, and a field between two associations, which is located on the southwestern edge of the shell and accounts for the general background field of the galaxy. The HST WFPC2 observations reach magnitudes as faint as V=25 mag, much deeper than have been observed earlier in stellar associations in the LMC. We determine the mass function (MF) for main-sequence stars in the areas. Its slope in both areas is steeper for stars with masses M<~2 M_solar (-4<~Γ<~-6) than for stars of M>~2 M_solar (-1<~Γ<~-2). Thus, as far as the field of the LMC is concerned, the MF does not have a uniform slope throughout its observed mass range. The MF of the general field of the LMC was found previously to be steeper than the MF of a stellar association for massive stars with M>~5 M_solar. We conclude that this seems to also be the case toward lower masses down to M~1 M_solar. Our data allow us to construct the field-subtracted, incompleteness-corrected, main-sequence MF of the southwestern part of the young stellar association LH 52, which accounts for the initial mass function (IMF) of the system. Its mean slope is found to be comparable to, but more shallow than, a typical Salpeter IMF (Γ~=-1.12+/-0.24) for masses down to ~1 M_solar. We found indications that the IMF of the association probably is ``top heavy,'' owing to the large number of intermediate-mass stars in the field of the system, while the general LMC field is found to be responsible for the low-mass population, with M<~2 M_solar, observed in both fields. This finding suggests that the local conditions seem to favor the formation of higher mass stars in associations, and not in the background field. No evidence for flattening of the IMF toward the low-mass regime or for a lower mass cutoff in the IMF was detected in our data.