Substellar Objects in Nearby Young Clusters (SONYC) IV: A census of very low mass objects in NGC1333

TL;DR

This study conducts a comprehensive census of very low mass objects, including brown dwarfs, in the NGC1333 cluster, revealing a higher-than-expected number of substellar objects and their spatial distribution, with implications for star formation theories.

Contribution

It provides the most extensive survey of substellar objects in NGC1333, identifying the lowest mass objects and analyzing their spatial and disk properties, highlighting environmental effects on formation.

Findings

Identified 10 new likely brown dwarfs with spectral types M6 or later.

Discovered objects with masses as low as 0.006 M_sun, the lowest in this cluster.

Found that brown dwarfs are spatially clustered similarly to stars.

Abstract

SONYC -- Substellar Objects in Nearby Young Clusters -- is a program to investigate the frequency and properties of young substellar objects with masses down to a few times that of Jupiter. Here we present a census of very low mass objects in the ~1 Myr old cluster NGC1333. We analyze near-infrared spectra taken with FMOS/Subaru for 100 candidates from our deep, wide-field survey and find 10 new likely brown dwarfs with spectral types of M6 or later. Among them, there are three with >~M9 and one with early L spectral type, corresponding to masses of 0.006 to <~0.02 Msol, so far the lowest mass objects identified in this cluster. The combination of survey depth, spatial coverage, and extensive spectroscopic follow-up makes NGC1333 one of the most comprehensively surveyed clusters for substellar objects. In total, there are now 51 objects with spectral type M5 or later and/or effective temperature of 3200 K or cooler identified in NGC1333; 30-40 of them are likely to be substellar. NGC1333 harbours about half as many brown dwarfs as stars, which is significantly more than in other well-studied star forming regions, thus raising the possibility of environmental differences in the formation of substellar objects. The brown dwarfs in NGC1333 are spatially strongly clustered within a radius of ~1 pc, mirroring the distribution of the stars. The disk fraction in the substellar regime is <66%, lower than for the total population (83%) but comparable to the brown dwarf disk fraction in other 2-3 Myr old regions.