The formation and evolution of galaxies depends strongly on the gas they contain. The surface density of neutral gas in particular, has been found to roughly correlate with the surface star-formation rate in nearby galaxies. However, we know that the underlying relation is between molecular gas and star-formation so that the conversion from neutral gas to molecular gas must play a fundamental role. All these processes are still to be investigated at high redshift. I will summarise our current knowledge of the neutral gas seen in the distant Universe through absorption towards quasars, and describe the challenges to understand its relation with molecular gas and star-formation.

Page created on September 22, 2017.