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

This paper presents a large spectral line and continuum survey of 8 deeplyembedded, low-mass protostellar cores using the Submillimeter Array. Eachsource was observed in high excitation lines of some of the most commonmolecular species, CO, HCO+, CS, SO, H2CO, CH3OH and SiO. Line emission from 11species originating from warm and dense gas have been imaged at high angularresolution (1-3"; typically 200-600 AU) together with continuum emission at 230GHz (1.3 mm) and 345 GHz (0.8 mm). Compact continuum emission is observed forall sources which likely originates in marginally optically thick circumstellardisks, with typical lower limits to their masses of 0.1 M_sun (1-10% of themasses of their envelopes) and having a dust opacity law with betaapproximately 1. Prominent outflows are present in CO 2-1 observations in allsources: the most diffuse outflows are found in the sources with the lowestratios of disk-to-envelope mass, and it is suggested that these sources are ina phase where accretion of matter from the envelope has almost finished and theremainder of the envelope material is being dispersed by the outflows. Othercharacteristic dynamical signatures are found with inverse P Cygni profilesindicative of infalling motions seen in the 13CO 2-1 lines towardNGC1333-IRAS4A and -IRAS4B. Outflow-induced shocks are present on all scales inthe protostellar environments and are most clearly traced by the emission ofCH3OH in NGC1333-IRAS4A and -IRAS4B. These observations suggest that theemission of CH3OH and H2CO from these proposed "hot corinos" are related to theshocks caused by the protostellar outflows. Only one source, NGC1333-IRAS2A,has evidence for hot, compact CH3OH emission coincident with the embeddedprotostar.Comment: Accepted for publication in ApJ (52 pages; 9 figures). Abstract abridge