Q/W-band Observations toward Starless Cores in Orion (QWOSCO) I. Overview, Isotopologues, Isomers, and Complex Organics

TL;DR

This study presents wide-band spectral observations of 23 starless cores in Orion, detecting about 40 molecules, and analyzes their chemical compositions and isotopic ratios to understand early star formation chemistry.

Contribution

First comprehensive Q/W-band spectral survey of starless cores in Orion, identifying molecular inventories and isotopic ratios, and comparing chemical abundances across evolutionary stages.

Findings

Detected ~40 molecular species in starless cores.

Isotopologue and isomer ratios align with starless environment expectations.

Complex organic molecules are likely common in starless cores.

Abstract

Molecular inventories in starless cores are powerful tools for probing the physical and chemical structures at the earliest stages of star formation. Wide-band spectral scans are invaluable for obtaining a comprehensive view of the chemical composition. In this paper, we present the first results from the project Q/W-band Observations toward Starless Cores in Orion (QWOSCO), which uses the Yebes 40-m telescope to survey 23 starless cores in the Orion cloud at the Q (31.0--50.5 GHz) and W (71.1--91.4 GHz) bands with a total bandwidth of 40 GHz. We detect approximately 40 molecular species and derive their column densities, with each species exhibiting a characteristic spread of roughly one order of magnitude. The derived isomer and isotopologue column density ratios, including A/E, ortho/para, cyclic/linear, HNC/HCN, 12C/13C, 14N/15N, 16O/18O, 32S/34S, and D/H, are consistent with expectations for starless environments. Our results together with the literature suggest that the complex organic molecules (COMs) CH3OH and CH3CHO are both likely ubiquitous in starless cores. The column density ratio of CH3CHO with respect to CH3OH in starless cores are comparable or lower by a factor of around 25 than those in hot corinos at the protostellar stages if the CH3OH column density is directly derived or rescaled from that of 13CH3OH, respectively. Accordingly, we discuss the possible roles of methanol opacity and chemical mechanisms across the starless and protostellar stages.