The effect of models of the interstellar media on the central mass distribution of galaxies

We compared the central mass distribution of dwarf and spiral galaxies simulated with three different models of the interstellar medium with increasing complexity: primordial (H+He) cooling, additional cooling via metal lines, and molecular hydrogen ( H₂) with shielding of atomic and molecular hydrogen, in addition to metal-line cooling. We followed the evolution of four high-resolution, simulated galaxies with V_peak < 120 km s^-1 to a redshift of zero in a fully cosmological Λ cold dark matter context. The spiral galaxies produced with either primordial cooling or H₂ physics had realistic, rising rotation curves. However, the simulations with metal-line cooling produced spiral galaxies with peaked rotation curves. These differences represent changes to the amount of low-angular-momentum baryons removed by stellar feedback. When there was only primordial cooling, the star-forming gas was hotter and the feedback-heated gas cooled relatively slowly so less energy was required to expel it. When H₂ was included, the accompanying shielding produced large amounts of clumpy, cold gas, and the supernova feedback was more highly concentrated. In contrast to the spiral galaxies, the dwarfs had similarly realistic concentrations and displayed similar behaviour across all models because their low metallicities resulted in smaller differences is the behaviour of the gas.