Atomic and molecular gas in simulated galaxies
Current hydrodynamical cosmological simulations such as Illustris cannot explicitly follow the complex chemical reaction network necessary to self-consistently compute the abundance of different species such as atomic (HI) and molecular (H2) gas. Those abundances, however, are key when comparing to observations which typically constrain either HI or H2 rather than the total gas content of galaxies.
Thus, the abundances are typically computed via post-processing (e.g., Lagos et al. 2015). The predictions can be based on observed correlations (e.g., Leroy et al. 2008), detailed simulations including a full reaction network (e.g., Gnedin & Kravtsov 2011), or analytical models of individual gas clouds (e.g., Krumholz 2013). I am currently testing and comparing the predictions of those and other models in order to understand the systematic uncertainties in the predictions and to compare Illustris TNG galaxies with HI observations. This project is in progress, a publication is in preparation.