Constraints on the IMF and the brown dwarf population of the young cluster IC 348

Abstract

We use a deep near-infrared census of the young stellar cluster IC 348 to construct and analyze its luminosity function. Our mosaic image of IC 348 covers the full extent of the cluster with a completeness limit of J ∼ 19.5 and is therefore sensitive for 2 Myr old cluster members with masses as low as M ≥ 0.005 M⊙ for the mean extinction of the known cluster members (AV ∼ 3.5 mag). By using information on stellar ages, extinctions, and the binary population in IC 348 from several recent studies, we can derive statistical constraints on the stellar and sub-stellar mass function of the cluster by modeling the observed luminosity function. We find that the stellar part of the mass function in IC 348 is well described by the galactic field star IMF. While several brown dwarfs have recently been identified in IC 348, our data show that the cluster harbors only a relatively small population of sub-stellar objects. We find that brown dwarfs in the mass range 0.02-0.075 M⊙ constitute at most ∼10% of the total cluster population, in contrast to recent results suggesting much larger brown dwarf populations in other young clusters and also the galactic field. Our results suggest that IC 348 has ∼2× fewer brown dwarfs than the Orion Trapezium cluster. A similar brown dwarf "deficit" was recently found in the Taurus star forming region. We speculate about the possible causes for this result, including the presence or absence of nearby massive stars and their influence on the formation of low-mass young stellar objects.