Asymmetric HI 21 cm lines of fast radio burst hosts: connection with galaxy interaction

TL;DR

This study analyzes atomic gas properties of a small sample of FRB host galaxies, revealing their interaction and asymmetric HI lines, which suggest a link between galaxy interactions and the origins of fast radio bursts.

Contribution

First analysis of atomic gas in FRB hosts showing their interaction and asymmetric HI lines, indicating recent star formation and possible progenitor channels.

Findings

All three FRB hosts are interacting galaxies.

FRB hosts with HI data show highly asymmetric spectra.

One FRB host is gas-deficient, others have normal gas properties.

Abstract

Fast radio bursts (FRBs) are enigmatic transients with very short radio emission. Their nature is still widely debated. I provide the first analysis of atomic gas properties of a small sample of FRB hosts to constrain their nature. HI observations exist for NGC 3252, the host of FRB 181030A, M81, the host of FRB 200120E, and the Milky Way, the host of FRB 200428. I report three observables: i) all three FRB hosts are interacting galaxies; ii) the Hi spectra of both FRB hosts with such data available are highly asymmetric, several standard deviations above the general population of galaxies; iii) two FRB hosts have normal atomic gas properties and one is strongly deficient in atomic gas. This indicates that nearby and repeating FRBs are connected with a recent enhancement of star formation due to interaction. This supports fast FRB channels, for example a massive star with a short delay time so that interaction signatures giving rise to the birth of the progenitor are still visible. Long gamma-ray burst (GRB) and broad-lined type Ic supernova (SN) hosts exhibit much more symmetric spectra, even though they were claimed to experience gas inflow from the intergalactic medium. The difference can be explained by the interactions experienced by FRB hosts being more disruptive than these gas inflows, or by the mass effect, with GRB/SN hosts at lower masses having less organized gas motions, so with HI lines closer to a symmetrical Gaussian. This also suggests that the emission mechanisms of FRBs and GRBs are different.