n 8.0\% Determination of the Baryon Fraction in the Intergalactic Medium from Localized Fast Radio Bursts

he 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 baryonfraction in the IGM ($f_{\mathrm{IGM}}$) and its degeneracy with cosmologicalparameters impose restrictions on the cosmological applications of FRBs.Furthermore, DMs contributed by the IGM ($\mathrm{DM_{IGM}}$) and host galaxy($\mathrm{DM_{host}}$), important cosmological quantities, cannot be exactlyextracted from observations, which would bring uncontrolled systematicuncertainties in FRB cosmology. In this work, we use seventeen localized FRBsto constrain $f_{\mathrm{IGM}}$ and its possible redshift evolution. Othercosmological probes such as type Ia supernovae, baryon acoustic oscillations,and cosmic microwave background radiation are combined to break parameterdegeneracy. Taking into account the probability distributions of$\mathrm{DM_{IGM}}$ and $\mathrm{DM_{host}}$ derived from the the IllustrisTNGsimulation, we obtain a robust measurement of $f_{\mathrm{IGM}}=0.927\pm0.075$,representing a precision of 8.0\%. We find that there is no strong evidence forthe redshift dependence of $f_{\mathrm{IGM}}$ at the current observational datalevel. The rapid progress in localizing FRBs will significantly improve theconstraints on $f_{\mathrm{IGM}}$.