A new way of detecting intergalactic baryons

TL;DR

This paper proposes a novel method to detect intergalactic baryons by analyzing short-timescale intensity variations in quasar light caused by plasma dispersion effects, enabling 3D mapping of ionized matter.

Contribution

It introduces a new observational technique using millisecond-scale intensity fluctuations to measure intergalactic plasma distribution along multiple lines of sight.

Findings

Dispersion causes detectable intensity fluctuations in quasar light.

Monitoring quasar light curves reveals intergalactic plasma distribution.

Method enables 3D mapping of baryonic matter in the universe.

Abstract

For each photon wave packet of extragalactic light, the dispersion by line-of-sight intergalactic plasma causes an increase in the envelope width and a chirp (drift) in the carrier frequency. It is shown that for continuous emission of many temporally overlapping wave packets with random epoch phases, such as quasars in the radio band, this in turn leads to quasi-periodic variations in the intensity of the arriving light on timescales between the coherence time (defined as the reciprocal of the bandwidth of frequency selection, taken here as of order 0.01 GHz for radio observations) and the stretched envelope, with most of the fluctuation power on the latter scale which is typically in the millisecond range for intergalactic dispersion. Thus, by monitoring quasar light curves on such short scales, it should be possible to determine the line-of-sight plasma column along the many directions and distances to the various quasars, affording one a 3-dimensional picture of the ionized baryons in the near universe.