A 7.0\% Determination of the Baryon Fraction in the Intergalactic Medium from Localized Fast Radio Bursts

Bao Wang and Jun-Jie Wei

Submitted on 3 November 2022


The dispersion measure (DM)--redshift relation of fast radio bursts (FRBs) has been proposed as a potential new tool for probing intergalactic medium (IGM) and for studying cosmology. However, the poor knowledge of the baryon fraction in the IGM (fIGM) and its degeneracy with cosmological parameters impose restrictions on the cosmological applications of FRBs. Furthermore, DMs contributed by the IGM (DMIGM) and host galaxy (DMhost), the important cosmological quantities, cannot be exactly extracted from observations, which would bring uncontrolled systematic uncertainties in FRB cosmology. In this work, we use seventeen localized FRBs to constrain fIGM and possibly its redshift evolution. Other cosmological probes such as Type Ia supernovae, baryon acoustic oscillations, and cosmic microwave background radiation are combined to break parameter degeneracy. Taking into account the probability distributions of DMIGM and DMhost derived from the the IllustrisTNG simulation, we obtain a robust measurement of fIGM=0.857±0.060, representing a precision of 7.0\%. We find that there is no strong evidence for the redshift dependence of fIGM at the current observational data level. The rapid progress in localizing FRBs will significantly improve the constraints on fIGM.


Comment: 9 pages, 3 figures, 2 tables

Subjects: Astrophysics - Cosmology and Nongalactic Astrophysics; Astrophysics - High Energy Astrophysical Phenomena


The $\mathrm{DM_{IGM}}$-$z$ relation for 17 localized FRBs. Data points are estimations of $\mathrm{DM_{IGM}}$ versus redshift measurements for 17 localized FRBs. The $\mathrm{DM_{IGM}}$ values are estimated by correcting the observed $\mathrm{DM_{obs}}$ for the contributions from our Galaxy and the FRB host galaxy (see text for details). The solid line shows model of Equation~(\ref{DMIGM}) with the inferred parameters $\Omega_{m}=0.309\pm0.006$, $\Omega_{b}h^2=0.02245\pm0.00013$, $H_{0}=67.73\pm0.44$ $\mathrm{km\;s^{-1}\;Mpc^{-1}}$, and $f_{\mathrm{IGM,0}}=0.857\pm0.060$. The shaded area, estimated by 1000 Monte Carlo simulations, represents the uncertainty of the theoretical $\mathrm{DM_{IGM}}$ value at 95\% confidence level due to the uncertainties of the inferred model parameters.