A Study of the Luminosity and Mass Functions of the Young IC 348 Cluster Using FLAMINGOS Wide-Field Near-Infrared Images

Abstract

We present wide-field near-infrared (JHK) images of the young, τ=2 Myr IC 348 cluster taken with FLAMINGOS. We use these new data to construct an infrared census of sources, which is sensitive enough to detect a 10 MJup brown dwarf seen through an extinction of AV~7. We examine the cluster's structure and relationship to the molecular cloud and to construct the cluster's K-band luminosity function. Using our model luminosity function algorithm, we derive the cluster's initial mass function (IMF) throughout the stellar and substellar regimes and find that the IC 348 IMF is very similar to that found for the Trapezium cluster, with both cluster IMFs having a mode between 0.2-0.08 Msolar. In particular, we find that, similar to our results for the Trapezium, brown dwarfs constitute only one in four of the sources in the IC 348 cluster. We show that a modest secondary peak forms in the substellar IC 348 K-band luminosity function (KLF), corresponding to the same mass range responsible for a similar KLF peak found in the Trapezium. We interpret this KLF peak as either evidence for a corresponding secondary IMF peak at the deuterium burning limit or as arising from a feature in the substellar mass-luminosity relation that is not predicted by current theoretical models. Finally, we find that IC 348 displays radial variations of its subsolar (0.5-0.08 Msolar) IMF on a parsec scale. Whatever mechanism that is breaking the universality of the IMF on small spatial scales in IC 348 does not appear to be acting on the brown dwarf population, whose relative size does not vary with distance from the cluster center.