The Host-Galaxy Dispersion Contribution Inferred from Localised Bursts

This paper subtracts modelled Galactic and computed intergalactic contributions from the dispersion measures of seven localised fast radio bursts with known redshifts, deriving the host-galaxy contribution for each under one uniform convention and characterising the resulting distribution and its consequences for dispersion-based distances. The headline results are as follows. Median observer-frame host dispersion of the sample: 121 pc cm-3; Median rest-frame host dispersion of the sample: 125 pc cm-3; Largest observer-frame host dispersion in the sample: 324 pc cm-3; Smallest observer-frame host dispersion in the sample: 42.9 pc cm-3; Intergalactic dispersion predicted at the sample median redshift: 251 pc cm-3; Host dispersion of the repeater FRB 180916 in its rest frame: 125 pc cm-3. All values are computed from the stated assumptions and published inputs; the study is simulated and computed, not measured.