Journal Article

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

Q. Liu, R. De Grijs, L. C. Deng, Y. Hu, I. Baraffe and S. F. Beaulieu

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 396, issue 3, pages 1665-1674
Published in print July 2009 | ISSN: 0035-8711
Published online June 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14838.x
The initial mass function of the rich young cluster NGC 1818 in the Large Magellanic Cloud

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We use deep Hubble Space Telescope photometry of the rich, young (∼20– to 45–Myr old) star cluster NGC 1818 in the Large Magellanic Cloud to derive its stellar mass function (MF) down to ∼0.15 M. 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 M, 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 Γ= 0.46 ± 0.10 and Γ≃−1.35 (Salpeter–like) for masses in the range from 0.15 to 0.8 M and greater than 0.8 M, respectively. Within the uncertainties, the NGC 1818 IMF is fully consistent with both the Kroupa solar neighbourhood and the Chabrier lognormal mass distributions.

Keywords: stars: low–mass, brown dwarfs; stars: luminosity function, mass function; stars: pre–main–sequence; Magellanic Clouds; galaxies: star clusters

Journal Article.  8054 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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