ALMA Observations of Starless Core Substructure in Ophiuchus
Di Francesco, J.; Sadavoy, S. I.; Johnstone, D.; Bourke, T. L.; Pineda, J. E.; Kirk, H.; Mairs, S.; Myers, P. C.; Shirley, Y. L.; Schnee, S.; Offner, S. S. R.; Arce, H. G.; Dunham, M. M.; Tobin, J. J.
Canada, United States, United Kingdom, Germany
Abstract
Compact substructure is expected to arise in a starless core as mass becomes concentrated in the central region likely to form a protostar. Additionally, multiple peaks may form if fragmentation occurs. We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations of 60 starless and protostellar cores in the Ophiuchus molecular cloud. We detect eight compact substructures which are > 15\prime\prime from the nearest Spitzer young stellar object. Only one of these has strong evidence for being truly starless after considering ancillary data, e.g., from Herschel and X-ray telescopes. An additional extended emission structure has tentative evidence for starlessness. The number of our detections is consistent with estimates from a combination of synthetic observations of numerical simulations and analytical arguments. This result suggests that a similar ALMA study in the Chamaeleon I cloud, which detected no compact substructure in starless cores, may be due to the peculiar evolutionary state of cores in that cloud.