  Using the results of the IllustrisTNG simulation we estimate the dispersion
measure which may be attributed to halos of so called host galaxies of fast
radio bursts sources (FRBs). Our results show that in contradiction to
assumptions used to show the applicability of FRBs to cosmological tests, both
the dispersion measure and its standard deviation calculated for host galaxies
with given stellar mass in general increase with the redshift. The effect is
not strong and cosmological tests using FRBs will be possible, but to preserve
the level of statistical uncertainty the number of FRBs with known redshift in
a sample should be increased by 15%--35% depending on circumstances. We show
various statistical characteristics of ionized gas surrounding galaxies, the
resulting dispersion measure and their dependence on the host galaxy stellar
mass, redshift, and the projected distance of a FRB source from its host
center.
  Cosmology: theory -- Galaxies: halos -- large-scale structure of Universe
