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, S. F. Beaulieu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)1665-1674
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - Jul 2009
Externally publishedYes


  • stars: low-mass, brown dwarfs
  • stars: luminosity function, mass function
  • stars: pre-main-sequence
  • Magellanic Clouds
  • galaxies: star clusters


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