Predictions for dispersion measures of fast radio bursts through the epoch of reionization using CoDa II

Dispersion measures (DM) of fast radio bursts (FRBs) probe the density of electrons in the intergalactic medium along their lines of sight, including the average density versus distance to the source and its variations in direction. While previous study focused on low redshift (e.g.), FRBs are potentially detectable out to high redshift, where their DMs can, in principle, probe the epoch of reionization (EoR) and its patchiness. We combine the cosmic density and ionization fields from large-scale radiation-hydro simulation Cosmic Dawn (CoDa) II of fully coupled galaxy formation and reionization to (where reionization ended at), with those from N-body simulation CoDa II-Dark Matter for the fully ionized post-EoR, from to the present. By calculating the mean and standard deviation of FRB DMs as functions of their source redshift, we are able to quantify the combined effect of self-consistent inhomogeneous density and ionization fields on FRB DMs for the first time. The mean and standard deviation of DM increase with redshift, and, assuming the CoDa reionization history, both reach a plateau by, i.e. well above. The mean-DM asymptote reflects the end of the EoR and its duration. The standard deviation there is, reflecting inhomogeneities of both patchy reionization and density. Inhomogeneities in ionization during the EoR contribute per cent) of this value of from FRBs at redshifts. Current estimates of FRB rates suggest this may be detectable within a few years of observation.