Molecular gas properties in interacting and merging galaxies

Molecular line emission is a useful tool for probing the highly obscured inner kpc of starburst galaxies – and of galaxies that harbour an enshrouded active nucleus. Molecular line ratios will serve as diagnostic tools of the physical conditions of the gas – but also of its chemical properties. Both provide important clues to the type and evolutionary stage of the nuclear activity – and how it can be connected to the interaction history of the galaxy. While 12CO emission remains the main tracer for molecular distribution and dynamics, molecules such as HCN, HNC, HCO+ and CN are useful for probing the properties of the denser (n ≳ 104 cm−3), star forming gas. The 12CO/13CO 1–0 and 2–1 line ratio reveals the impact of the nuclear activity on the interstellar medium – as well as probing the effect of dynamics on the properties of the molecular gas.