Modification of the 21-cm power spectrum by quasars during the epoch of reionisation

TL;DR

This paper investigates how high-redshift quasars influence the 21-cm power spectrum during reionisation, showing they significantly alter its amplitude and shape, which must be considered in future models.

Contribution

It introduces a semi-numerical scheme incorporating quasars into 21-cm power spectrum simulations, highlighting their impact on reionisation signals.

Findings

Quasars modify the power spectrum amplitude and shape.

Quasar ionising photons are more biased than stellar photons.

Quasar effects are comparable to their fractional contribution to reionisation.

Abstract

We assess the effect of a population of high-redshift quasars on the 21-cm power spectrum during the epoch of reionisation. Our approach is to implement a semi-numerical scheme to calculate the three-dimensional structure of ionised regions surrounding massive halos at high redshift. We include the ionising influence of luminous quasars by populating a simulated overdensity field with quasars using a Monte Carlo Markov Chain algorithm. We find that quasars modify both the amplitude and shape of the power spectrum at a level which is of the same order as the fractional contribution to reionisation. The modification is found both at constant redshift and at constant global neutral fraction, and arises because ionising photons produced by quasars are biased relative to the density field at a level that is higher than steller ionising photons. Our results imply that quasar ionisation will need to be included in detailed modelling of observed 21-cm power spectra.