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 ALMA Cycle 2 observations of 60 starless and protostellar cores in the Ophiuchus molecular cloud. We detect eight compact substructures which are >15 arcsec from the nearest Spitzer YSO. 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.
@article{arxiv.1703.00506,
title = {ALMA Observations of Starless Core Substructure in Ophiuchus},
author = {Helen Kirk and Michael M. Dunham and James Di Francesco and Doug Johnstone and Stella S. R. Offner and Sarah I. Sadavoy and John J. Tobin and Hector G. Arce and Tyler L. Bourke and Steve Mairs and Philip C. Myers and Jaime E. Pineda and Scott Schnee and Yancy L. Shirley},
journal= {arXiv preprint arXiv:1703.00506},
year = {2017}
}