The molecular diversity of the ISM in galaxies across cosmic time

TL;DR

The paper argues that our understanding of extragalactic ISM chemistry is currently limited by sensitivity- and area-restricted surveys that focus on a few bright galaxies. It advocates a next-generation, wide-field, multi-species, multi-transition observational program using facilities like AtLAST to map molecular gas across cosmic time, from the early universe to today. It outlines two central science cases—constructing molecular inventories across cosmic time and measuring the full molecular gas budget—supported by examples such as ALCHEMI and the need to calibrate tracers like [CII] and [CI] in low-metallicity environments. Together, these efforts will provide robust chemical diagnostics of ISM processes, enabling a deeper understanding of how gas responds to environment and how the baryon cycle drives galaxy formation and evolution.

Abstract

Submillimetre molecular lines (e.g., CO, HCN, SiO) provide a uniquely powerful view of the physical and chemical processes that govern star formation (SF) and galaxy evolution. Yet, our current picture of the molecular universe beyond the Milky Way remains strikingly incomplete: broad chemical inventories exist for only a handful of galaxies, typically more extreme than the Milky Way, constrained by sensitivity limits and narrow survey strategies. In the 2040s, surveying galaxies with multi-species, multi-transitions observations across diverse galactic environments will be crucial to establish effective chemical diagnostics of the various ISM processes from the early universe to $z=0$. Extragalactic astrochemistry provides a uniquely sensitive probe of the physical processes shaping galaxies, allowing us to understand, species by species, how gas responds to its local environment and how galaxies grow, transform, and recycle matter over cosmic time.

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