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

TL;DR

This study reveals the widespread presence and distinct spatial distributions of methanol and related molecules in starless cores of Orion, highlighting environmental effects and the need for high-resolution observations to understand early star formation chemistry.

Contribution

It provides the first detailed spatial analysis of methanol and related molecules in Orion starless cores, demonstrating their ubiquity and environmental dependence.

Findings

Methanol detected in all cores, confirming its ubiquity.

Distinct spatial distributions of molecules suggest environmental influences.

Outer layer localization of CCS and c-C3HD relative to N2H+.

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.