This week at AIMS we were all set to hear about recent progress in the formation and evolution of galaxies from Guinevere Kauffman who was visiting us from Max-Planck-Institut für Astrophysik. However, after a quick poll of the audience and a gauge of our interests Guinevere deftly switched to a more detailed discussion of her recent work on modelling the evolution of HI and H2 in galaxies with Jian Fu, Qi Guo, Cheng Li and the COLD GASS and GASS teams.
Guinevere began by explaining how the data with which the model was compared was collected. The data came from two sources: GASS (Galax Arecibo SDSS Survey) which provided measurements of HI and COLD GASS (CO Legacy Database for GASS) which looked for molecular gas.
After summarizing the criteria for selecting galaxies for the survey, Guinevere moved on to tell about the semi-analytic model of gas that was examined. This model combined merger tree data from N-body simulations (the MILLENNIUM simulations) with differential equations describing the evolution of cold gas into stars into hot gas into stars etc. By adding in radial information about the location of the gas to this model Guinevere and her collaborators produced a more detailed model, which they then (mostly) confirmed by comparing the predicted gas profiles with a sample from THINGS/HERACLES data.
Guinevere then told us how the model could be used to explain some of the global scaling relations between the stellar mass, atomic gas mass and molecular gas mass in an ensemble of galaxies. After explaining various physical drivers of the scaling, (including the halo mass, the spin parameter and the fraction of recent accretion), Guinevere moved on to tell us how the models held up against data.
The galaxies with and without detected gas were analysed separately, with the former testing the disk formation model and the latter testing “quenching” processes. Guinevere explained to us that while the disk formation model matched the detected data very well, this was not the case for those galaxies with undetected gas. This in turn, she suggested, meant that internal processes (e.g. black holes or bulges) rather than the halo were responsible for shutting down galaxies.
Guinevere finished her talk by discussing how future measurements of gas might be improved, using as an example work with her collaborator Cheng Li on measuring HI by looking at photometric predictors, in particular UV emission.