Cosmology-independent Estimate of the Fraction of Baryon Mass in the IGM from Fast Radio Burst Observations

Zhengxiang Li,Bing Zhang,He Gao,Yuan-Pei Yang,Zong-Hong Zhu,Jun-Jie Wei

doi:10.3847/1538-4357/ab18fe

Abstract

Abstract The excessive dispersion measure (DM) of fast radio bursts (FRBs) has been proposed to be a powerful tool to study intergalactic medium (IGM) and to perform cosmography. One issue is that the fraction of baryons in the IGM, f IGM, is not properly constrained. Here, we propose a method of estimating f IGM using a putative sample of FRBs with the measurements of both DM and luminosity distance d L. The latter can be obtained if the FRB is associated with a distance indicator (e.g., a gamma-ray burst or a gravitational-wave event), or the redshift z of the FRB is measured and d L at the corresponding z is available from other distance indicators (e.g., SNe Ia) at the same redshift. As d L/DM essentially does not depend on cosmological parameters, our method can determine f IGM independent of cosmological parameters. We parameterize f IGM as a function of redshift and model the DM contribution from a host galaxy as a function of star formation rate. Assuming f IGM has a mild evolution with redshift with a functional form and by means of Monte Carlo simulations, we show that an unbiased and cosmology-independent estimate of the present value of f IGM with a ∼12% uncertainty can be obtained with 50 joint measurements of d L and DM. In addition, such a method can also lead to a measurement of the mean value of DM contributed from the local host galaxy.

Highlights

Fast radio bursts (FRBs) are a class of bright transients with millisecond durations detected at ∼GHz (Lorimer et al 2007; Thornton et al 2013; Petroff et al 2015, 2016)
Even if FRBs are not associated with distance indicators, as long as its z is measured, one may obtain its dL using that of other indicators at the same redshift
The intergalactic medium (IGM) portion of the dispersion measure (DM), i.e., DMIGM depends on the cosmological distance scale the burst passes through and the fraction of ionized electrons in hydrogen (H, χe,H(z)) and helium (He, χe,He(z)) on the path, which are closely related to the present-day baryon density parameter Ωb and fraction of baryons in the IGM (Deng & Zhang 2014)

Summary

Introduction

Fast radio bursts (FRBs) are a class of bright transients with millisecond durations detected at ∼GHz (Lorimer et al 2007; Thornton et al 2013; Petroff et al 2015, 2016). Mass of the photon (Wu et al 2016; Shao & Zhang 2017), measuring the cosmic proper distance (Yu & Wang 2017), as well as constraining the magnetic fields in the IGM (Akahori et al 2016) Thanks to another two properties of these mysterious transients, i.e., narrow durations (∼(1–10) ms; Lorimer et al 2007; Keane et al 2011; Thornton et al 2013; Spitler et al 2014; Petroff et al 2015; Ravi et al 2015; Champion et al 2016; Petroff et al 2016; Spitler et al 2016) and a high event rate (∼103–104 per day all sky; Thornton et al 2013; Champion et al 2016), lensed FRBs have been proposed as a probe of compact dark matter (Muñoz et al 2016; Wang & Wang 2018), motion of the FRB source (Dai & Lu 2017), as well as precision cosmology (Li et al 2018). Through Monte Carlo simulations, we show that both the fraction of baryons in the IGM and the mean value of the local host galaxy DM can be unbiasedly inferred from such joint measurements in a cosmological-model-independent way

Luminosity Distance versus Dispersion Measure

Redshift Distribution and Uncertainties of the Parameters

Monte Carlo Simulations and Fitting Results

Conclusions and Discussions