Characterizing fast radio bursts through statistical cross-correlations

TL;DR

This paper explores how cross-correlating fast radio bursts with galaxy catalogs can determine their redshift distribution without needing precise host galaxy identification, leveraging statistical methods and propagation effects.

Contribution

It introduces a forecasting method for estimating FRB redshift distribution through cross-correlation with galaxy surveys, bypassing the need for arcsecond localization.

Findings

Cross-correlation can constrain FRB redshift distribution with few-arcminute resolution.

Propagation effects from free electrons influence FRB-galaxy correlations.

Disentangling effects reveals insights into FRBs and free electron clustering.

Abstract

Understanding the origin of fast radio bursts (FRB's) is a central unsolved problem in astrophysics that is severely hampered by their poorly determined distance scale. Determining the redshift distribution of FRB's appears to require arcsecond angular resolution, in order to associate FRB's with host galaxies. In this paper, we forecast prospects for determining the redshift distribution without host galaxy associations, by cross-correlating FRB's with a galaxy catalog such as the SDSS photometric sample. The forecasts are extremely promising: a survey such as CHIME/FRB that measures catalogs of $\sim 10^3$ FRB's with few-arcminute angular resolution can place strong constraints on the FRB redshift distribution, by measuring the cross-correlation as a function of galaxy redshift $z$ and FRB dispersion measure $D$. In addition, propagation effects from free electron inhomogeneities modulate the observed FRB number density, either by shifting FRB's between dispersion measure (DM) bins or through DM-dependent selection effects. We show that these propagation effects, coupled with the spatial clustering between galaxies and free electrons, can produce FRB-galaxy correlations which are comparable to the intrinsic clustering signal. Such effects can be disentangled based on their angular and $(z, D)$ dependence, providing an opportunity to study not only FRB's but the clustering of free electrons.