The cosmic abundance of molecular gas in the local universe
Thomas Fletcher
University College London (UCL)
Amelie Saintonge (UCL)
Galaxy evolution is closely tied to the abundance of gas. Cold molecular gas is accreted along cosmic filaments, into the dark matter halos of galaxies, where it collapses to form dense clouds of gas. It is in these conditions that star formation can occur. Galaxy growth is then regulated by outflows of gas due to supernovae explosions and active galactic nuclei, these processes deplete the galaxy of gas, thus slowing the rate of star formation. Hence, the history and evolution of a galaxy is closely linked to the history and evolution of gas and its conversion into stars.

It is therefore necessary to have a good understanding of the cosmic abundance of atomic and molecular gas (Ω_HI and Ω_H2 respectively) throughout the history of the Universe to understand galaxy growth and to constrain galaxy evolution models. Currently, there is no definitive value for Ω_H2 in the local Universe with previous research deriving this value using a biased sample, mostly comprised of irregular galaxies (spirals and mergers).

In this MSc project, Ω_H2 is derived at z = 0 using a non-biased sample of main sequence star forming galaxies from the COLD GASS survey. As the COLD GASS survey only contains galaxies with log (M/M*) > 9, empirical scaling relations are used to complete the hydrogen mass function at lower masses in a representative manner. Mock catalogues from cosmological simulations will also be used to complete the sample at lower masses.