Abstract

We characterize protostellar multiplicity in (20) Current address: Niels Bohr Institute, University of Copenhagen, oster Voldgade 5a euro "7, DK-1350, Copenhagen K, Denmark. the Orion molecular clouds using Atacama Large Millimeter/submillimeter Array 0.87 mm and Very Large Array 9 mm continuum surveys toward 328 protostars. These observations are sensitive to projected spatial separations as small as similar to 20 au, and we consider source separations up to 10(4) au as potential companions. The overall multiplicity fraction (MF) and companion fraction (CF) for the Orion protostars are 0.30 +/- 0.03 and 0.44 +/- 0.03, respectively, considering separations from 20 to 10(4) au. The MFs and CFs are corrected for potential contamination by unassociated young stars using a probabilistic scheme based on the surface density of young stars around each protostar. The companion separation distribution as a whole is double peaked and inconsistent with the separation distribution of solar-type field stars, while the separation distribution of Flat Spectrum protostars is consistent solar-type field stars. The multiplicity statistics and companion separation distributions of the Perseus star-forming region are consistent with those of Orion. Based on the observed peaks in the Class 0 separations at similar to 100 au and similar to 10(3) au, we argue that multiples with separations <500 au are likely produced by both disk fragmentation and turbulent fragmentation with migration, and those at greater than or similar to 10(3) au result primarily from turbulent fragmentation. We also find that MFs/CFs may rise from Class 0 to Flat Spectrum protostars between 100 and 10(3) au in regions of high young stellar object density. This finding may be evidence for the migration of companions from >10(3) au to <10(3) au, and that some companions between 10(3) and 10(4) au must be (or become) unbound.