On the origin of planetary-mass objects in NGC 1333

The dominant formation mechanism of brown dwarfs and planetary-mass objects (PMOs) in star-forming regions is presently uncertain. Do they form like stars, via the collapse and fragmentation of cores in giant molecular clouds, or do they form like planets in the discs around stars and are ejected via dynamical interactions? In this paper, we quantify the spatial distribution of substellar objects in NGC 1333, in particular focusing on PMOs that have been the target of recent deep imaging observations. We find that these objects have a spatial distribution that is indistinguishable from the stars, and more massive brown dwarfs. We also analyse N-body simulations and find that a population of ejected planets would have a significantly different spatial and kinematic distribution from stars, and brown dwarfs that also formed through gravitational collapse and fragmentation. We therefore conclude that the low-mass substellar objects in NGC 1333 formed more like stars than planets, although we predict that a population of hitherto undetected ejected PMOs may be lurking in this and other star-forming regions.