The initial mass function of the rich young cluster NGC 1818 in the Large Magellanic Cloud |
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Authors: | Q Liu R de Grijs L C Deng Y Hu I Baraffe S F Beaulieu |
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Institution: | National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, P. R. China;Graduate University of the Chinese Academy of Sciences, Beijing 100049, P. R. China;Department of Physics and Astronomy, The University of Sheffield, Sheffield S3 7RH;CRAL, École Normale Supérieure, 46 allée d'Italie, 69007 Lyon, France;Département de Physique, de Génie Physique et d'Optique and Centre de Recherche en Astrophysique du Québec, UniversitéLaval, Québec, QC G1V 0A6, Canada |
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Abstract: | 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. |
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Keywords: | stars: low-mass brown dwarfs stars: luminosity function mass function stars: pre-main-sequence Magellanic Clouds galaxies: star clusters |
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