2020ApJ...900..170Z

We calculate the dispersion measures (DMs) contributed by host galaxies of fast radio bursts (FRBs). Based on a few host galaxy observations, a large sample of galaxies with similar properties to observed ones has been selected from the IllustrisTNG simulation. They are used to compute the distributions of host galaxy DMs for repeating and nonrepeating FRBs. For repeating FRBs, we infer the DM_host for FRBs like FRB 121102 and FRB 180916 by assuming that the burst sites are tracing the star formation rates in host galaxies. The median DMs_host are 35 (1 + z)^1.08 and 96(1 + z)^0.83 pc cm^–3 for FRBs like FRB 121102 and FRB 180916, respectively. In another case, the median of DM_host is about 30-70 pc cm^–3 for nonrepeating FRBs in the redshift range z = 0.1-1.5, assuming that the burst sites are the locations of binary neutron star mergers. In this case, the evolution of the median DM_host can be calculated by 33(1 + z)^0.84 pc cm^–3. The distributions of DM_host of repeating and nonrepeating FRBs can be well fitted with the log-normal function. Our results can be used to infer redshifts of nonlocalized FRBs.