HI asymmetries in spatially resolved SIMBA galaxies

TL;DR

This study uses cosmological simulations to analyze the asymmetries in neutral hydrogen distributions of galaxies, comparing synthetic data with observations to understand the impact of galaxy interactions on HI morphology.

Contribution

It introduces a method to quantify HI asymmetries in simulated galaxies and compares these with observations, highlighting the limitations of using spectral asymmetry alone.

Findings

Interacted and merged galaxies show higher HI asymmetries than isolated ones.

SIMBA galaxies' HI size-mass relation closely matches observations, with slight size discrepancies.

Spectral asymmetry correlates weakly with morphological asymmetry, especially in disturbed galaxies.

Abstract

We present a study of the neutral atomic hydrogen (HI) content of spatially resolved, low-redshift galaxies in the SIMBA cosmological simulations. We create synthetic HI data cubes designed to match observations from the Apertif Medium-Deep HI imaging survey, and follow an observational approach to derive the HI size-mass relation. The HI 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 HI mass. We quantify the HI spectral ($A_{\mathrm{flux}}$) and morphological ($A_{\mathrm{mod}}$) asymmetries of the galaxies and motivate standardizing the relative spatial resolution when comparing values in a sample that spans several orders of magnitude in HI 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 HI reservoirs. We determine that the interacted and merged categories have higher mean asymmetries than the isolated category, with a larger separation between the categories' $A_{\mathrm{mod}}$ distributions than between their $A_{\mathrm{flux}}$ distributions. For the interacted and merged categories, we find an inverse correlation between baryonic mass and $A_{\mathrm{mod}}$ that is not observed between baryonic mass and $A_{\mathrm{flux}}$. These results, coupled with the weak correlation found between $A_{\mathrm{flux}}$ and $A_{\mathrm{mod}}$, highlight the limitations of only using $A_{\mathrm{flux}}$ to infer the HI distributions of spatially unresolved HI detections.