Modeling the atomic-to-molecular transition in cosmological simulations of galaxy formation

Understand

Large-scale cosmological simulations of galaxy formation currently do not resolve the densities at which molecular hydrogen forms, implying that the atomic-to-molecular transition must be modeled either on the fly or in postprocessing.

• We present an improved postprocessing framework to estimate the abundance of atomic and molecular hydrogen and apply it to the IllustrisTNG simulations.
• We compare five different models for the atomic-to-molecular transition, including empirical, simulation-based, and theoretical prescriptions.
• Most of these models rely on the surface density of neutral hydrogen and the ultraviolet (UV) flux in the Lyman-Werner band as input parameters.