H I asymmetries in spatially resolved simba galaxies

Abstract

We present a study of the neutral atomic hydrogen (H I) content of spatially resolved, low-redshift galaxies in the SIMBA cosmological simulations. We create synthetic H I data cubes designed to match observations from the Apertif Medium-Deep H I imaging survey, and follow an observational approach to derive the H I size–mass relation. The H I size–mass relation for sIMBA is in broad agreement with the observed relation to within 0.1 dex, but SIMBA galaxies are slightly smaller than expected at fixed H I mass. We quantify the H I spectral (Aflux) and morphological (Amod) asymmetries of the galaxies and motivate standardizing the relative spatial resolution when comparing Amod values in a sample that spans several orders of magnitude in H I mass. Galaxies are classified into three categories (isolated, interacted, or merged) based on their dynamical histories over the preceding ∼2 Gyr to contextualize disturbances in their H I reservoirs. We determine that the interacted and merged categories have higher mean asymmetries than the isolated category, with a larger separation between the categories’ Amod distributions than between their Aflux distributions. For the interacted and merged categories, we find an inverse correlation between baryonic mass and Amod that is not observed between baryonic mass and Aflux. These results, coupled with the weak correlation found between Aflux and Amod, highlight the limitations of only using Aflux to infer the H I distributions of spatially unresolved H I detections.