Towards a consistent model for both the H I and stellar mass functions of galaxies

Using the L-Galaxies semi-analytic model we simultaneously fit the H I mass function, stellar mass function and the fraction of red galaxies.We find good fits to all three observations at z= 0 and to the stellar mass function and red fraction at z = 2. Using Markov Chain Monte Carlo (MCMC) techniques we adjust the L-Galaxies parameters to best fit the constraining data. In order to fit the H I mass function we must greatly reduce the gas surface density threshold for star formation, thus lowering the number of low H I mass galaxies. A simultaneous reduction in the star formation efficiency prevents the overproduction of stellar content. A simplified model in which the surface density threshold is eliminated altogether also provides a good fit to the data. Unfortunately, these changes weaken the fit to the Kennicutt–Schmidt relation and raise the star formation rate density at recent times, suggesting that a change to the model is required to prevent accumulation of gas on to dwarf galaxies in the local Universe.