Testing the role of environmental effects on the initial mass function of low-mass stars

Abstract

ABSTRACT In the star-formation process, the vital impact of environmental factors such as feedback from massive stars and stellar density on the form of the initial mass function (IMF) at the low-mass end is yet to be understood. Hence a systematic highly sensitive observational analysis of a sample of regions under diverse environmental conditions is essential. We analyse the IMF of eight young clusters (<5 Myr), namely IC 1848-West, IC 1848-East, NGC 1893, NGC 2244, NGC 2362, NGC 6611, Stock 8, and Cygnus OB2, which are located at the Galactocentric distance (Rg) range ∼6–12 kpc along with the nearby cluster IC 348 using deep near-IR photometry and Gaia DR2. These clusters are embedded in massive stellar environments of radiation strength $\log(L_\mathrm{FUV}/\mathrm{L}_{\odot })\, \sim 2.6$–6.8, $\log(L_\mathrm{EUV})\, \sim$ 42.2–50.85 photon s−1, with stellar density in the range of ∼170–1220 star pc−2. After structural analysis and field decontamination we obtain an unbiased uniformly sensitive sample of pre-main-sequence members of the clusters down to the brown-dwarf regime. The lognormal fit to the IMF of nine clusters gives the mean characteristic mass (mc) and σ of 0.32 ± 0.02 M⊙ and 0.47 ± 0.02, respectively. We compare the IMF with that of low- and high-mass clusters across the Milky Way. We also check for any systematic variation with respect to the radiation field strength and the stellar density as well with Rg. We conclude that there is no strong evidence for an environmental effect in the underlying form of the IMF of these clusters.