Extracting host galaxy dispersion measure and constraining cosmological parameters using fast radio burst data

TL;DR

This paper proposes a new method to extract host galaxy dispersion measures and constrain cosmological parameters using fast radio burst data, relying on a slope parameter that can be directly measured from FRB samples with known redshifts.

Contribution

The study introduces a novel slope parameter $eta(z)$ that enables direct measurement of host galaxy DM contributions and cosmological parameters from FRB data without heavy assumptions.

Findings

The slope parameter $eta(z)$ can be measured from FRB samples with known redshifts.

Monte Carlo simulations show that host galaxy DM and cosmological parameters can be independently constrained.

The method allows estimation of local host galaxy DM and key cosmological parameters through MCMC fitting.

Abstract

The excessive dispersion measures (DMs) and high Galactic latitudes of fast radio bursts (FRBs) hint toward a cosmological origin of these mysterious transients. Methods of using measured DM and redshift $z$ to study cosmology have been proposed, but one needs to assume a certain amount of DM contribution from the host galaxy (DM$_{\rm HG}$) in order to apply those methods. We introduce a slope parameter $\beta(z) \equiv d \ln \left< {\rm DM}_{\rm E} \right> / d \ln z$ (where DM$_{\rm E}$ is the observed DM subtracting the Galactic contribution), which can be directly measured when a sample of FRBs have $z$ measured. We show that $\left< {\rm DM_{HG}}\right>$ can be roughly inferred from $\beta$ and the mean values, $\overline{\rm \left<DM_{\rm E}\right>}$ and $\bar z$, of the sample. Through Monte Carlo simulations, we show that the mean value of local host galaxy DM, $\left<\rm{DM_{HG,loc}}\right>$, along with other cosmological parameters (mass density $\Omega_m$ in the $\Lambda$CDM model, and the IGM portion of the baryon energy density $\Omega_b f_{\rm IGM}$) can be independently measured through MCMC fitting to the data.