The Distribution of Atomic Hydrogen in the Host Galaxies of FRBs

TL;DR

This study investigates the atomic hydrogen properties of FRB host galaxies, revealing that most are massive and star-forming, but do not show a significant excess of disturbance compared to typical galaxies, challenging previous assumptions.

Contribution

It provides the first comprehensive analysis showing that HI disturbance is not a universal feature of FRB hosts, contrasting earlier suggestions of a connection to merger activity.

Findings

Most FRB hosts are HI-massive and star-forming.

Disturbed HI morphology is not universal among FRB hosts.

No significant excess of HI disturbance compared to general galaxy population.

Abstract

We probe the atomic hydrogen (HI) emission from the host galaxies of fast radio bursts (FRBs) to investigate the emerging trend of disturbance and asymmetry in the population. Quadrupling the sample size, we detect 16 out of 17 new hosts in HI, with the single non-detection arising in a galaxy known to be transitioning towards quiescence. With respect to typical local Universe galaxies, FRB hosts are generally massive in HI ($M_{HI}>10^9 M_\odot$), which aligns with previous studies reporting that FRB hosts also tend to have high stellar masses and are star-forming. However, they span a broad range of other HI derived properties. Using visual inspection alongside various asymmetry metrics, we identify six unambiguously settled host galaxies, demonstrating for the first time that a disturbed HI morphology is not a universal feature of FRB host galaxies. However, we find another six that show clear signs of disturbance, one borderline case, and three which require deeper or more targeted observations to reach a conclusion; this brings the confirmed ratio of disturbed-to-settled FRB hosts to 11:6. Given that roughly a 1:1 ratio is expected for random background galaxies of similar type, our observed ratio yields a p-value of 0.222. Therefore, we conclude that contrary to earlier indications, there is no statistically significant excess of HI disturbance in this sample of FRB host galaxies with respect to the general galaxy population, and hence we find no evidence for a fundamental connection between FRB progenitor formation and merger-induced star formation activity.