Substellar Objects in Nearby Young Clusters (SONYC): The bottom of the Initial Mass Function in NGC1333

Abstract

SONYC -- Substellar Objects in Nearby Young Clusters -- is a survey program to investigate the frequency and properties of substellar objects with masses down to a few times that of Jupiter in nearby star-forming regions. Here we present the first results from SONYC observations of NGC1333, a ~1Myr old cluster in the Perseus star-forming complex. We have carried out extremely deep optical and near-infrared imaging in four bands (i', z', J, K) using Suprime-Cam and MOIRCS instruments at the Subaru telescope. The survey covers 0.25sqdeg and reaches completeness limits of 24.7mag in the i'-band and 20.8mag in the J-band. We select 196 candidates with colors as expected for young, very low-mass objects. Follow-up multi-object spectroscopy with MOIRCS is presented for 53 objects. We confirm 19 objects as likely brown dwarfs in NGC1333, seven of them previously known. For 11 of them, we confirm the presence of disks based on Spitzer/IRAC photometry. The effective temperatures for the brown dwarf sample range from 2500K to 3000K, which translates to masses of ~0.015 to 0.1Ms. For comparison, the completeness limit of our survey translates to mass limits of 0.004Ms for Av<~5mag or 0.008Ms for Av<~ 10mag. Compared with other star-forming regions, NGC1333 shows an overabundance of brown dwarfs relative to low-mass stars, by a factor of 2-5. On the other hand, NGC1333 has a deficit of planetary-mass objects: Based on the surveys in SOrionis, the ONC and Cha I, the expected number of planetary-mass objects in NGC1333 is 8-10, but we find none. It is plausible that our survey has detected the minimum mass limit for star formation in this particular cluster, at around 0.012-0.02Ms. If confirmed, our findings point to significant regional/environmental differences in the number of brown dwarfs and the minimum mass of the IMF. (abridged)

19 pages, 12 figures, accepted for publication in ApJ

References in corpus (29)

• Empirical Color Transformations Between SDSS Photometry and Other Photometric Systems
• Subaru Deep Survey V. A Census of Lyman Break Galaxies at z=4 and 5 in the Subaru Deep Fields: Photometric Properties
• Spitzer Observations of NGC 1333: A Study of Structure and Evolution in a Nearby Embedded Cluster
• Star formation through gravitational collapse and competitive accretion
• The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation
• The Stellar Population of the Chamaeleon I Star-Forming Region
• The COMPLETE Survey of Star-Forming Regions: Phase I Data
• Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
• Gravitational fragmentation and the formation of brown dwarfs in stellar clusters
• A Spitzer census of the IC 348 nebula
• The minimum mass for star formation, and the origin of binary brown dwarfs
• Consistent simulations of substellar atmospheres and non-equilibrium dust-cloud formation
• Near-infrared cross-dispersed spectroscopy of brown dwarf candidates in the Upper Sco association
• A Large-Area Search for Low Mass Objects in Upper Scorpius I: The Photometric Campaign and New Brown Dwarfs
• Young, Low-Mass Brown Dwarfs with Mid-Infrared Excesses
• Evidence for a Turnover in the IMF of Low Mass Stars and Sub-stellar Objects: Analysis from an Ensemble of Young Clusters
• New brown dwarfs in Upper Sco using UKIDSS Galactic Cluster Survey science verification data
• Direct evidence of a sub-stellar companion around CT Cha
• New Low-Mass Stars and Brown Dwarfs with Disks in the Chamaeleon I Star-Forming Region
• Infrared Spectroscopy and Analysis of Brown Dwarf and Planetary Mass Objects in the Orion Nebula Cluster
• A Large Scale Survey of NGC1333
• Contamination by field late-M, L and T dwarfs in deep surveys
• The lower mass function of the young open cluster Blanco 1: from 30 Mjup to 3 Mo
• Spectroscopy of planetary mass brown dwarfs in Orion
• New members in the Upper Sco association from the UKIDSS Early Data Release
• A Spectroscopic Study of Young Stellar Objects in the Serpens Cloud Core and NGC 1333
• A deep look into the cores of young clusters I. sigma-Orionis
• Planetesimals To Brown Dwarfs: What is a Planet?
• HST/NICMOS Observations of NGC 1333: The Ratio of Stars to Sub-Stellar Objects