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

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(IGM). Using the measured dispersion measure (DM) and luminosity distance d(L) data (inferred from the FRB redshifts and d(L) of Type Ia supernovae at the same redshifts) of the five FRBs, we constrain the local f(IGM) = 0.84(-0.22)(+0.16) with no evidence of redshift dependence. This cosmology-insensitive estimate of f(IGM) 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(IGM) = 0.74(-0.18)(+0.24). In these two cases, reasonable estimations for the host galaxy DM contribution (DMhost) can be achieved by modelling it as a function of star formation rate. The constraints on both f(IGM) and DMhost are expected to be significantly improved with the rapid progress in localizing FRBs.