The initial mass function of the rich young cluster NGC 1818 in the Large Magellanic Cloud

TL;DR

This study derives the initial mass function of the young star cluster NGC 1818 in the Large Magellanic Cloud using deep Hubble data, providing insights into stellar populations in low-metallicity environments.

Contribution

First robust measurement of the low-mass stellar mass function in an extragalactic, low-metallicity cluster down to 0.15 solar masses.

Findings

IMF well described by lognormal and broken power-law models

IMF consistent with Kroupa and Chabrier distributions

Derived IMF slopes: Gamma=0.46 for low masses, Gamma~-1.35 for higher masses

Abstract

We use deep Hubble Space Telescope photometry of the rich, young (~20-45 Myr-old) star cluster NGC 1818 in the Large Magellanic Cloud to derive its stellar mass function (MF) down to ~0.15 Msun. This represents the deepest robust MF thus far obtained for a stellar system in an extragalactic, low-metallicity ([Fe/H]~-0.4 dex) environment. Combining our results with the published MF for masses above 1.0 Msun, we obtain a complete present-day MF. This is a good representation of the cluster's initial MF (IMF), particularly at low masses, because our observations are centred on the cluster's uncrowded half-mass radius. Therefore, stellar and dynamical evolution of the cluster will not have affected the low-mass stars significantly. The NGC 1818 IMF is well described by both a lognormal and a broken power-law distribution with slopes of Gamma=0.46+/-0.10 and Gamma~-1.35 (Salpeter-like) for masses in the range from 0.15 to 0.8 Msun and greater than 0.8 Msun, respectively. Within the uncertainties, the NGC 1818 IMF is fully consistent with both the Kroupa solar-neighbourhood and the Chabrier lognormal mass distributions.