SONYC: Sub-stellar Objects in Nearby Young Clusters

The origin of the lowest mass free-floating objects, i.e. brown dwarfs (BDs) and planetary mass object, is one of the major unsolved questions in star formation. Various competing origin theories exist, such as turbulent fragmentation, dynamical decay of mini-clusters, ejection from protoplanetary disks, and these theories are increasingly capable of providing predictions for the frequency and properties of substellar objects. A fundamental prerequisite to test these theories is to establish a census of young brown dwarfs. Such a census allows us to probe the initial mass function (IMF), binary statistics, and properties of accretion disks. SONYC: Substellar Objects in Nearby Young Clusters, has been an ongoing survey program since 2007 to provide a substellar population census in nearby star forming regions. The survey is based on wide-field, deep optical and near-infrared imaging, combined with proper motions and archival catalogs, followed up by extensive spectroscopic campaigns with Subaru and VLT that resulted in more than 700 spectra of candidate objects in NGC1333, Rho Ophiuchi, Chamaeleon-I, Upper Sco, and Lupus-3. We present the major survey results: 1. The discovery and characterisation of 60+ new substellar objects, including a handful of objects with masses close to, or below the Deuterium burning limit. 2. Through SONYC and similar surveys by other groups, the substellar IMF is now well characterized down to 5-10 Mjup, with the number of BDs per 10 stars constrained to 2.5-5 in clusters. This is presently in disagreement with the results from the field population, where fewer BDs per star are found. 3. Down to ~5 Mjup, free-floating planetary mass objects are observed to be rare, 20-50 times less numerous than stars. This implies that their total contribution to the mass budget of the clusters can be neglected. Spectra, photometric catalogues, and links to the SONYC publications are available at: http:/browndwarfs.org/sonyc