The complete census of molecular hydrogen in a simulated disc galaxy

TL;DR

This study uses high-resolution simulations to map molecular hydrogen distribution in a galaxy, revealing the importance of resolution for accurate H2 formation modeling and its complex interstellar medium behavior.

Contribution

It provides a comprehensive, multi-scale analysis of molecular hydrogen in a simulated galaxy, highlighting the impact of resolution on H2 formation and distribution.

Findings

High-resolution simulations are crucial for accurate H2 modeling.

A significant fraction of H2 exists in low-density, hard-to-observe regions.

Simulation results agree with observations where data is available.

Abstract

We present a multi-scale analysis of molecular hydrogen in a Milky Way-like simulated galaxy. Our census covers the gas content of the entire disc, to radial profiles and the Kennicutt-Schmidt relation, to a study of its molecular clouds, and finally down to a cell-by-cell analysis of the gas phases. Where observations are available we find agreement. A significant fraction of the H2 gas is in low-density regions mixed with atomic hydrogen and would therefore be difficult to observe. We use the molecular addition to ramses-rt, an adaptive mesh refinement grid code with the hydrodynamics coupled to moment-based radiative transfer. Three resolutions of the same galaxy detail the effects it has on H2 formation, with grid cells sized 97, 24, and 6.1 pc. Only the highest resolution yields gas densities high enough to host significant H2 fractions, and resolution is therefore key to simulating H2. Apart our pieces of galactic analysis are disparate, but assembled they provide a cohesive portrait of H2 in the interstellar medium. H2 chemistry on the atomic scale is sufficient to generate its dynamics throughout an entire galaxy.