# Estimates of Fast Radio Burst Dispersion Measures from Cosmological Simulations

## TL;DR

This paper uses cosmological simulations to estimate the intergalactic medium's dispersion measure contribution to fast radio bursts, providing insights into their redshifts and host galaxy contributions.

## Contribution

It introduces a novel method to calculate the IGM dispersion measure using large-scale cosmological simulations and applies it to real FRB observations.

## Key findings

- Estimated IGM DM at z=1: 800^{+7000}_{-170} pc cm^{-3}
- Most probable host galaxy DM for FRB 121102: ~310 pc cm^{-3}
- Consistent host galaxy DM estimate with spectral data

## Abstract

We calculate the dispersion measure (DM) contributed by the intergalactic medium (IGM) to the total measured DM for fast radio bursts (FRBs). We use the MareNostrum Instituto de Ciencias del Espacio (MICE) Onion Universe simulation (Fosalba et al. 2008) to track the evolution of the dark matter particle density over a large range of redshifts. We convert this dark matter particle number density to the corresponding free electron density and then integrate it to find the DM as a function of redshift. This approach yields an intergalactic DM of $\rm DM_{\rm IGM}(z = 1) = 800^{+7000}_{-170}$ pc cm$^{-3}$, with the large errors representative of the structure in the IGM. We place limits on the redshifts of the current population of observed FRBs. We also use our results to estimate the host galaxy contribution to the DM for the first repeater, FRB 121102, and show that the most probable host galaxy DM contribution, $\rm DM_{\rm host} \approx 310$ pc cm$^{-3}$, is consistent with the estimate made using the Balmer emission lines in the spectrum of the host galaxy, $\rm DM_{\rm Balmer} = 324$ pc cm$^{-3}$ (Tendulkar et al. 2017). We also compare our predictions for the host galaxy contribution to the DM for the observations of FRB 180924 (Bannister et al. 2019) and FRB 190523 (Ravi et al. 2019), both of which have been localized to a host galaxy.