The low-mass content of the massive young star cluster RCW 38

Koraljka Mužić, Rainer Schödel, Alexander Scholz, Vincent C. Geers, Ray Jayawardhana, Joana Ascenso, Lucas A. Cieza

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23 Citations (Scopus)


RCW 38 is a deeply embedded young (∼1 Myr), massive star cluster located at a distance of 1.7 kpc. Twice as dense as the Orion nebula cluster, orders of magnitude denser than other nearby star-forming regions and rich in massive stars, RCW 38 is an ideal place to look for potential differences in brown dwarf formation efficiency as a function of environment. We present deep, high-resolution adaptive optics data of the central ∼0.5 × 0.5 pc2 obtained with NACO at the Very Large Telescope. Through comparison with evolutionary models, we determine masses and extinction for ∼480 candidate members, and derive the first initial mass function (IMF) of the cluster extending into the substellar regime. Representing the IMF as a set of power laws in the form dN/dMM−α, we derive the slope α = 1.60 ± 0.13 for the mass range 0.5–20 M,which is shallower than the Salpeter slope, but in agreement with results in several other young massive clusters. At the low-mass side, we find α = 0.71 ± 0.11 for masses between 0.02 and 0.5 M, or α = 0.81 ± 0.08 for masses between 0.02 and 1 M. Our result is in agreement with the values found in other young star-forming regions, revealing no evidence that a combination of high stellar densities and the presence of numerous massive stars affects the formation efficiency of brown dwarfs and very-low-mass stars. We estimate that the Milky Way galaxy contains between 25 and 100 billion brown dwarfs (with masses >0.03 M).
Original languageEnglish
Pages (from-to)3699-3712
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date27 Jul 2017
Publication statusPublished - 1 Nov 2017


  • Brown dwarfs
  • Stars: formation
  • Stars: luminosity function
  • Mass function
  • Stars: pre-main sequence
  • Open clusters and associations: individual: RCW 38


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