Cosmology-insensitive estimate of IGM baryon mass fraction from five localized fast radio bursts

Abstract

Five fast radio bursts (FRBs), including three apparently non-repeating ones, FRB 180924, FRB 181112, and FRB 190523, and two repeaters, FRB 121102 and FRB 180916.J0158+65, have already been localized so far. We apply a method developed recently by us to these five localized FRBs to give a cosmology-insensitive estimate of the fraction of baryon mass in the intergalactic medium, f<inf>IGM</inf>. Using the measured dispersion measure (DM) and luminosity distance d<inf>L</inf> data (inferred from the FRB redshifts and d<inf>L</inf> of Type Ia supernovae at the same redshifts) of the five FRBs, we constrain the local $f-{rm IGM} = 0.84{+0.16}-{-0.22}$ with no evidence of redshift dependence. This cosmology-insensitive estimate of f<inf>IGM</inf> from FRB observations is in excellent agreement with previous constraints using other probes. Moreover, using the three apparently non-repeating FRBs only we get a little looser but consistent result: $f-{rm IGM} = 0.74{+0.24}-{-0.18}$. In these two cases, reasonable estimations for the host galaxy DM contribution (DM<inf>host</inf>) can be achieved by modelling it as a function of star formation rate. The constraints on both f<inf>IGM</inf> and DM<inf>host</inf> are expected to be significantly improved with the rapid progress in localizing FRBs.