# ALMA Observations of Starless Core Substructure in Ophiuchus

## TL;DR

This study uses ALMA observations to investigate substructure in starless cores within the Ophiuchus cloud, finding limited evidence of compact substructures and discussing implications for core evolution and comparison with other regions.

## Contribution

First ALMA survey of starless cores in Ophiuchus revealing the presence and rarity of compact substructures, informing core evolution models.

## Key findings

- Detected 8 compact substructures, mostly associated with protostellar activity.
- Number of detections aligns with simulation-based predictions.
- Differences with Chamaeleon I suggest evolutionary state influences core substructure.

## 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 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.