NEATH IV: an early onset of complex organic chemistry in molecular clouds

TL;DR

This study demonstrates that complex organic molecules form early in molecular clouds, prior to core formation, suggesting that chemical complexity begins well before star and planet formation, impacting models of astrochemical evolution.

Contribution

It reveals that COMs form at modest densities before core formation, emphasizing the importance of early dynamical phases in astrochemical models.

Findings

COMs form at densities of a few 10^3 cm^-3 before core formation

Much COM-enriched material remains at modest densities for several Myr

Models should incorporate early dynamical evolution for accurate chemistry predictions

Abstract

Complex organic molecules (COMs) are widely detected in protostellar and protoplanetary systems, where they are thought to have been inherited in large part from earlier evolutionary phases. The chemistry of COMs in these earlier phases, namely starless and prestellar cores, remains poorly understood, as models often struggle to reproduce the observed gas-phase abundances of these species. We simulate the formation of a molecular cloud, and the cores within it, out of the diffuse interstellar medium, and follow the chemical evolution of the cloud material starting from purely-atomic initial conditions. We find that the formation of both gas- and ice-phase COMs precedes the formation of cores as distinct objects, beginning at gas densities of a few $10^3 \,{\rm cm}^{-3}$. Much of this COM-enriched material remains at these relatively modest densities for several Myr, which may provide a reservoir for accretion onto planet-forming discs in later evolutionary stages. We suggest that models of core and disc chemistry should not ignore the complex dynamical evolution which precedes these structures, even when studying supposedly late-forming molecules such as CH$_3$OH and CH$_3$CN.