PROSAC: A Submillimeter Array Survey of Low‐Mass Protostars. I. Overview of Program: Envelopes, Disks, Outflows, and Hot Cores

Abstract

This paper presents a large spectral line and continuum survey of 8 deeply\nembedded, low-mass protostellar cores using the Submillimeter Array. Each\nsource was observed in high excitation lines of some of the most common\nmolecular species, CO, HCO+, CS, SO, H2CO, CH3OH and SiO. Line emission from 11\nspecies originating from warm and dense gas have been imaged at high angular\nresolution (1-3"; typically 200-600 AU) together with continuum emission at 230\nGHz (1.3 mm) and 345 GHz (0.8 mm). Compact continuum emission is observed for\nall sources which likely originates in marginally optically thick circumstellar\ndisks, with typical lower limits to their masses of 0.1 M_sun (1-10% of the\nmasses of their envelopes) and having a dust opacity law with beta\napproximately 1. Prominent outflows are present in CO 2-1 observations in all\nsources: the most diffuse outflows are found in the sources with the lowest\nratios of disk-to-envelope mass, and it is suggested that these sources are in\na phase where accretion of matter from the envelope has almost finished and the\nremainder of the envelope material is being dispersed by the outflows. Other\ncharacteristic dynamical signatures are found with inverse P Cygni profiles\nindicative of infalling motions seen in the 13CO 2-1 lines toward\nNGC1333-IRAS4A and -IRAS4B. Outflow-induced shocks are present on all scales in\nthe protostellar environments and are most clearly traced by the emission of\nCH3OH in NGC1333-IRAS4A and -IRAS4B. These observations suggest that the\nemission of CH3OH and H2CO from these proposed "hot corinos" are related to the\nshocks caused by the protostellar outflows. Only one source, NGC1333-IRAS2A,\nhas evidence for hot, compact CH3OH emission coincident with the embedded\nprotostar.\n