# Large host-galaxy dispersion measure of fast radio bursts

## TL;DR

This study develops a Bayesian method to estimate the mean host galaxy dispersion measure of FRBs, revealing a large average DM likely influenced by the host galaxy's ISM or local plasma, with implications for FRB host galaxy types.

## Contribution

The paper introduces a novel Bayesian approach to extract the mean host galaxy DM and luminosity of FRBs from observed data, assuming a narrow luminosity distribution.

## Key findings

- Mean host galaxy DM is approximately 270 pc cm^{-3}.
- Large host DM suggests non-Milky Way-like host galaxies.
- Possible contributions to DM include ISM, SNR, PWN, or HII regions.

## Abstract

Fast radio bursts (FRBs) have excessive dispersion measures (DMs) and an all-sky distribution, which point toward an extragalactic or even a cosmological origin. We develop a method to extract the mean host galaxy DM ($\left\langle{\rm DM_{HG,loc}}\right\rangle$) and the characterized luminosity ($L$) of FRBs using the observed DM-Flux data, based on the assumption of a narrow luminosity distribution. Applying Bayesian inference to the data of 21 FRBs, we derive a relatively large mean host DM, i.e. $\left\langle{\rm DM_{HG,loc}}\right\rangle \sim 270~\rm{pc~cm^{-3}}$ with a large dispersion. A relatively large ${\rm DM_{HG}}$ of FRBs is also supported by the millisecond scattering times of some FRBs and the relatively small redshift $z=0.19273$ of FRB 121102 (which gives ${\rm DM_{HG,loc}} \sim 210 ~\rm{pc~cm^{-3}}$). The large host galaxy DM may be contributed by the ISM or a near-source plasma in the host galaxy. If it is contributed by the ISM, the type of the FRB host galaxies would not be Milky Way (MW)-like, consistent with the detected host of FRB 121102. We also discuss the possibility of having a near-source supernova remnant (SNR), pulsar wind nebula (PWN) or HII region that gives a significant contribution to the observed ${\rm DM_{HG}}$.