Intergalactic medium dispersion measures of fast radio bursts estimated from IllustrisTNG simulation and their cosmological applications

TL;DR

This paper uses the IllustrisTNG simulation to estimate intergalactic medium dispersion measures of fast radio bursts up to high redshifts, enabling cosmological applications like probing reionization and CMB optical depth.

Contribution

It provides a realistic estimation of DM_IGM up to z~9 using simulations and explores its applications in constraining reionization history and measuring CMB optical depth.

Findings

DM_IGM at z=1 is 892^{+721}_{-270} pc cm^{-3}

DM distribution fits a quasi-Gaussian with a long tail

High-redshift DM_IGM constrains reionization redshift to z=5.95

Abstract

Fast radio bursts (FRBs) are millisecond-duration radio transients and can be used as a cosmological probe. However, the dispersion measure (DM) contributed by intergalactic medium (IGM) is hard to be distinguished from other components. In this paper, we use the IllustrisTNG simulation to realistically estimate the $DM_{\rm IGM}$ up to $z\sim 9$. We find $DM_{\rm IGM} = 892^{+721}_{-270}$ pc cm$^{-3}$ at $z=1$. The probability distribution of $DM_{\rm IGM}$ can be well fitted by a quasi-Gaussian function with a long tail. The tail is caused by the structures along the line of sight in IGM. Subtracting DM contributions from the Milky Way and host galaxy for localized FRBs, the $DM_{\rm IGM}$ value is close to the derived $DM_{\rm IGM}-z$ relation. We also show the capability to constrain the cosmic reionization history with the $DM_{\rm IGM}$ of high-redshift FRBs in the IllustrisTNG universe. The derived $DM_{\rm IGM}-z$ relation at high redshifts can be well fitted by a $tanh$ reionization model with the reionization redshift $z=5.95$, which is compatible with the reionization model used by the IllustrisTNG simulation. The $DM_{\rm IGM}$ of high-redshift FRBs also provides an independent way to measure the optical depth of cosmic microwave background (CMB). Our result can be used to derive the pseudo-redshifts of non-localized FRBs for $DM_{\rm IGM}<4000$ \ \ pc cm$^{-3}$.