Constraining the Cosmic Baryon Distribution with Fast Radio Burst Foreground Mapping

The dispersion measure of fast radio bursts (FRBs) encodes the integrated electron density along the line of sight, which is typically dominated by the intergalactic medium contribution in the case of extragalactic FRBs. In this paper, we show that incorporating wide-field spectroscopic galaxy survey data in the foreground of localized FRBs can significantly improve constraints on the partition of diffuse cosmic baryons. Using mock dispersion measures and realistic light-cone galaxy catalogs derived from the Millennium simulation, we define spectroscopic surveys that can be carried out with 4 and 8 m class wide-field spectroscopic facilities. On these simulated surveys, we carry out Bayesian density reconstructions in order to estimate the foreground matter density field. In comparison with the true matter density field, we show that these can help reduce the uncertainties in the foreground structures by similar to 2-3x compared to cosmic variance. We calculate the Fisher matrix to forecast that N = 30 (96) localized FRBs should be able to constrain the diffuse cosmic baryon fraction to similar to 10% (similar to 5%) and parameters governing the size and baryon fraction of galaxy circumgalactic halos to within similar to 20%-25% (similar to 8%-12%). From the Fisher analysis, we show that the foreground data increase the sensitivity of localized FRBs toward our parameters of interest by similar to 25x. We briefly introduce FLIMFLAM, an ongoing galaxy redshift survey that aims to obtain foreground data on similar to 30 localized FRB fields.

Automated summary

This paper shows that incorporating wide-field spectroscopic galaxy survey data in the foreground of localized FRBs can significantly improve constraints on the partition of diffuse cosmic baryons. By using mock dispersion measures and realistic light-cone galaxy catalogs, the authors perform Bayesian density reconstructions to estimate the foreground matter density field and demonstrate that these data can reduce uncertainties in foreground structures and increase the sensitivity of localized FRBs towards parameters of interest.