Dispersion Distance and the Matter Distribution of the Universe in Dispersion Space

TL;DR

This paper explores using dispersion measurements from fast radio bursts as a novel way to map the universe's large-scale structure, accounting for dispersion space distortions caused by electron density inhomogeneities.

Contribution

It introduces the concept of dispersion space as a new cosmological distance measure and models how FRB clustering can reveal large-scale structure despite dispersion distortions.

Findings

Dispersion-space power spectra can be measured with around 10,000 FRB events.

Clustering signals in dispersion space are detectable with upcoming radio telescopes.

Dispersion distortions can be modeled to recover large-scale structure information.

Abstract

We propose that "standard pings", brief broadband radio impulses, can be used to study the three-dimensional clustering of matter in the Universe even in the absence of redshift information. The dispersion of radio waves as they travel through the intervening plasma can, like redshift, be used as a cosmological distance measure. Because of inhomogeneities in the electron density along the line of sight, dispersion is an imperfect proxy for radial distance and we show that this leads to calculable dispersion-space distortions in the apparent clustering of sources. Fast radio bursts (FRBs) are a new class of radio transients that are the prototypical standard ping and, due to their high observed dispersion, have been interpreted as originating at cosmological distances. The rate of fast radio bursts has been estimated to be several thousand over the whole sky per day and, if cosmological, the sources of these events should trace the large-scale structure of the Universe. We calculate the dispersion-space power spectra for a simple model where electrons and FRBs are biased tracers of the large-scale structure of the Universe and we show that the clustering signal could be measured using as few as 10 000 events. Such a survey is in line with what may be achieved with upcoming wide-field radio telescopes.