The Initial Mass Function and Young Brown Dwarf Candidates in NGC 2264. IV. The Initial Mass Function and Star Formation History

Abstract: We have studied the star formation history and the initial mass function (IMF) using the age and mass derived from spectral energy distribution (SED) fitting and from color-magnitude diagrams. We also examined the physical and structural parameters of more than 1,000 pre-main sequence stars in NGC 2264 using the on-line SED fitting tool (SED fitter) of Robitaille et al. The cumulative distribution of stellar ages showed a distinct difference among SFRs. The results indicate that star formation in NGC 2264 started at the surface region (Halo and Field regions) about 6 - 7 Myr ago, propagated into the molecular cloud and finally triggered the recent star formation in the Spokes cluster. The kind of sequential star formation that started in the low-density surface region (Halo and Field regions) implies that star formation in NGC 2264 was triggered by an external source. The IMF of NGC 2264 was determined in two different ways. The slope of the IMF of NGC 2264 for massive stars (log m >= 0.5) is -1.7 \pm 0.1, which is somewhat steeper than the so-called standard "Salpeter-Kroupa" IMF. We also present data for 79 young brown dwarf candidates.