The Complete Initial Mass Function Down to the Sub-Solar Regime in the Large Magellanic Cloud with Hubble Space Telescope ACS Observations

Abstract

In this photometric study of the stellar association LH 95 in the Large Magellanic Cloud (LMC) we focus on the pre-main Sequence (PMS) population in order to construct, for the first time, the sub-solar initial mass function (IMF) in the LMC. We use the deepest photometry ever performed in the LMC with the Advanced Camera for Surveys (ACS) on-board the Hubble Space Telescope(HST). We carry out a Monte Carlo technique to subtract the contribution of the general field of LMC and we isolate the central region in the observed area of the association. We study the mass function of its field-subtracted population. For this purpose, we introduce a new set of evolutionary models, derived from the calculations on the evolution of PMS stars by Siess et al. We use these models with our observations of LH 95 to derive the IMF of the system, which is reliably constructed down to 0.43 M_sun, the lowest mass ever observed within reasonable completeness in the Magellanic Clouds. Consequently, its construction offers an outstanding improvement in our understanding of the low-mass star formation in the LMC. The system IMF of LH 95 shows a definite change in its slope at 1 M_sun, where it becomes more shallow. In general, the shape of this IMF agrees very well with the average Galactic IMF, down to the sub-solar regime. As far as the slope of this system IMF is concerned, it is found to be somewhat more shallow than the corresponding classical Galactic IMF in the sub-solar regime, probably due to unresolved binarity, while for stars with M>1M_sun it becomes slightly steeper. We do not find significant differences in the shape of the overall IMF of LH 95 from that of each of the three individual sub-clusters, suggesting that the IMF of LH 95 is not subject to local variability.

19 pages, 13 figures. Accepted for publication to ApJ

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