Abstract

Contributed Talk - Splinter ALMA2040   (MW-2235)

Decoding the molecular ISM: why multi-line, multi-transition spectroscopy is the key to ALMA2040

Lukas Neumann
ESO

The physical conditions of the cold, molecular interstellar medium such as density, temperature, radiation field are encoded in the emission of molecular lines, but any single line or simple ratios between lines are degenerate with a range of physical states. Breaking these degeneracies requires confronting observations with models, whether radiative transfer, astrochemistry, or machine learning, and the power of any such approach scales directly with the number of independent lines available. Today, faint multi-transition tracers beyond the basic low-J CO transitions remain observable only for small samples or at coarse resolution, especially beyond the Milky Way. I argue that the order-of-magnitude gains in sensitivity and bandwidth anticipated for ALMA2040 would make routine, resolved, multi-line spectroscopy feasible across environments — from Galactic clouds to nearby galaxies and the high-redshift Universe — finally providing the data that modelling approaches need to deliver robust constraints on the cold ISM. I will review the current state of this field and outline how ALMA2040 would transform it.