Ubiquity of Methanol and Its Related Chemical Segregation in Orion Starless Cores: The ALMASOP Sample

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 CH 3 OH, N 2 H + , CCS, and c-C 3 HD, using the Atacama Compact Array (ACA) and the Yebes 40 m telescope. CH 3 OH was detected toward all targets, confirming its ubiquity in starless cores, consistent with previous surveys in Taurus and Perseus. ACA imaging shows that CH 3 OH, CCS, and c-C 3 HD generally trace the outer layers of the dense cores outlined by N 2 H + , each exhibiting distinct spatial distributions. Meanwhile, comparison with Yebes data reveals an extended, flattened CH 3 OH component. CCS and c-C 3 HD tend to be detected or nondetected 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-C 3 HD. 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.