Probing Diffuse Gas with Fast Radio Bursts

TL;DR

This paper explores the potential of using Fast Radio Bursts to probe diffuse gas in the universe, showing that current cosmological constraints can help measure the diffuse gas fraction and its evolution, which could address the missing baryon problem.

Contribution

The study demonstrates that FRB-based measurements can constrain the diffuse gas fraction and its redshift evolution, highlighting their role in resolving the missing baryon problem.

Findings

Current cosmological data can constrain the diffuse gas fraction to a few percent.

FRB observations can help measure the redshift evolution of diffuse gas.

Combining FRBs with other probes improves constraints on baryonic matter.

Abstract

The dispersion measure -- redshift relation of Fast Radio Bursts, $\mathrm{DM}(z)$, has been proposed as a potential new probe of the cosmos, complementary to existing techniques. In practice, however, the effectiveness of this approach depends on a number of factors, including (but not limited to) the intrinsic scatter in the data caused by intervening matter inhomogeneities. Here, we simulate a number of catalogues of mock FRB observations, and use MCMC techniques to forecast constraints, and assess which parameters will likely be best constrained. In all cases we find that any potential improvement in cosmological constraints are limited by the current uncertainty on the the diffuse gas fraction, $f_{\rm d}(z)$. Instead, we find that the precision of current cosmological constraints allows one to constrain $f_{\rm d}(z)$, and possibly its redshift evolution. Combining CMB + BAO + SNe + $H_0$ constraints with just 100 FRBs (with redshifts), we find a typical constraint on the mean diffuse gas fraction of a few percent. A detection of this nature would alleviate the "missing baryon problem", and therefore highlights the value of localisation and spectroscopic followup of future FRB detections.