Ubiquity of Methanol and its related Chemical Segregation in Orion Starless Cores: the ALMASOP Sample

TL;DR

The paper investigates how complex organic molecules manifest in starless cores within the Orion A and B clouds, addressing whether COM ubiquity and spatial segregation differ from better-studied regions like Taurus and Perseus. It reports a chemical survey of 16 cores (including five prestellar) targeting CH3OH, N2H+, CCS, and c-C3HD using the ALMA-ACA and the Yebes 40-m telescope. CH3OH is detected toward all targets, confirming ubiquity, while ACA imaging shows CH3OH, CCS, and c-C3HD tracing outer core layers delineated by N2H+, with an extended flattened CH3OH component seen in Yebes data. CCS and c-C3HD tend to co-occur or be absent together, and cores near dust-rich regions often lack both, suggesting environmental ISRF influences; within cores, CCS lies in the outer layer relative to c-C3HD. The study highlights the importance of high-resolution observations to understand the origins and spatial differentiation of COMs and carbon-chain molecules in cold, quiescent environments and to test desorption mechanisms under varying turbulence and radiation conditions.

Abstract

Complex organic molecules (COMs) in starless cores provide critical insights into the early stages of star formation and prebiotic chemistry. We present a chemical survey of 16 starless cores (including five prestellar cores) in the Orion A and B molecular clouds, targeting CH3OH, N2H+, CCS, and c-C3HD, using the Atacama Compact Array (ACA) and the Yebes 40-m telescope. CH3OH was detected toward all targets, confirming its ubiquity in starless cores, consistent with previous surveys in Taurus and Perseus. ACA imaging shows that CH3OH, CCS, and c-C3HD generally trace the outer layers of the dense cores outlined by N2H+, each exhibiting distinct spatial distributions. Meanwhile, Comparison with Yebes data reveals an extended, flattened CH3OH component. CCS and c-C3HD tend to be detected or non-detected together across cores, while cores near dust-rich regions on a large scale often lack both, suggesting environmental influences linked to the interstellar radiation field. Within individual cores, CCS typically resides in an outer layer relative to c-C3HD. Our findings underscore the importance of high-resolution studies for understanding the origins and spatial differentiation of COMs and carbon-chain molecules in cold, quiescent environments.