Probing the evolution of oxygen-bearing complex organic molecules (O-COMs) from ice to gas

Complex organic molecules (COMs), usually defined as carbon-containing molecules with at least six atoms, have attracted great interest serving as the first step from simple species toward the building blocks of life. So far, more than 100 COMs have been firmly or tentatively detected in space, and most of the detections were made toward protostellar cores (also called 'hot cores'). However, the transition from case studies (e.g., on Sgr B2 and IRAS 16293-2422) to large-sample surveys has only come forth in the recent five years or so. Here we report systematic studies on ten O-COMs in the gas phase toward a dozen high-mass protostars as a subsample of the Complex Chemistry in hot Cores with ALMA (CoCCoA) survey. In particular, our attention is drawn not only to those abundant O-COMs with 1-2 carbon atoms, but also those less studied larger molecules such as acetone (CH3COCH3) and propanal (C2H5CHO). We found intriguing trends that aldehydes (i.e., molecules with the CHO group) are overall less abundant than O-COMs of other types, while CH3-bearing molecules (such as CH3OCH3, CH3OCHO, and CH3COCH3) are generally the most abundant among the species with the same amount of C atoms. In the meantime, the gas abundances of some of the O-COMs are compared to their ice abundances, which have recently been derived from JWST/MIRI observations. By conducting gas-to-ice comparisons of O-COMs in the same sources, we can shed some light on their chemical evolution from ice to gas.