The origin and nature of molecular emission in galactic and extragalactic gas

It is now well established that chemistry in our own galaxy as well as in external galaxies can be complex and well-developed. In particular,
molecular emissions can be used to explore the physical conditions and the likely evolutionary status of near and far away galaxies. In this talk, I will review recent developments in observational as well as theoretical molecular astrophysics in the context of galactic, nearby and more distant galaxies.

I will show how, even for the most distant galaxies, multi-species multi-transitions molecular emissions can be used as a tool to 'disentangle' the multiple and spatially unresolved gas components, with particular emphasis on tracing the dense star forming gas within a galaxy.