FEASTS Compared with Simulations: Abnormally Irregular and Extended HI Morphologies at a Column Density of $10^{18}\,\text{cm}^{-2}$ in TNG50 and Auriga

TL;DR

This study compares low-column density HI morphologies between observations from FEASTS and simulations from TNG50 and Auriga, revealing discrepancies influenced by stellar feedback and magnetic fields, and highlighting the potential for observational constraints on galaxy simulations.

Contribution

It provides the first statistical comparison of HI morphology at low column densities between observations and cosmological simulations, identifying key feedback processes affecting morphology.

Findings

Over one-third of TNG50 galaxies show irregular HI morphology.

Stellar feedback correlates with morphological deviations from observations.

Magnetic fields may help produce more regular HI morphologies.

Abstract

With new atomic-hydrogen (HI) observations of FAST Extended Atlas of Selected Targets Survey (FEASTS), we present the first statistical comparison of HI morphology between observations and cosmological simulations, focusing on low-column density ($10^{18}\,\text{cm}^{-2}$) regions of Milky Way-like central galaxies. We select a 330-galaxy sample from IllustrisTNG50 (TNG50) matched to 33 FEASTS galaxies by stellar and HI masses, and mock observe them to the FAST resolution and depth at corresponding inclinations and distances for a fair comparison. In contrast to FEASTS, abnormally irregular and extended morphology is found in more than one-third of TNG50 galaxies, especially those massive and HI poor. Stellar feedback is the property that most significantly correlates with the HI morphological deviation from observations, although these deviations mostly occur at a high stellar or black-hole mass. These results indicate that in TNG50, stellar feedback significantly influences the HI morphology at $10^{18}\,\text{cm}^{-2}$, while active galactic nucleus (AGN) feedback has not so direct a role as expected. With an additional sample from Auriga, we find that the magnetic field may help HI to be more regular in its morphology, while improving the mass resolution does not alleviate the discrepancy from observation. This study reveals the potential of constraining future simulations of galaxies by observing low-column density HI.