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 (CO)-C-12 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 greater than or similar to 10(4) cm(-3)), star forming gas. The (CO)-C-12/(CO)-C-13 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. (c) 2006 Elsevier B.V. All rights reserved.