H I asymmetries in spatially resolved SIMBA galaxies

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 (A_flux) and morphological (A_mod) asymmetries of the galaxies and motivate standardizing the relative spatial resolution when comparing A_mod 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’ A_mod distributions than between their A_flux distributions. For the interacted and merged categories, we find an inverse correlation between baryonic mass and A_mod that is not observed between baryonic mass and A_flux. These results, coupled with the weak correlation found between A_flux and A_mod, highlight the limitations of only using A_flux to infer the H I distributions of spatially unresolved H I detections.