Lyalpha versus X-ray heating in the high-z IGM

TL;DR

This study investigates the relative impact of X-ray and Lyalpha photons on heating the high-redshift intergalactic medium, highlighting conditions under which X-ray heating dominates and implications for 21 cm signals.

Contribution

It presents self-consistent cosmological simulations analyzing photon production from stars and micro-quasars, revealing the dominant heating mechanisms in the early universe.

Findings

X-ray heating generally dominates over Lyalpha unless low-mass star-forming objects significantly enhance Lyalpha emission.

Gas temperature surpasses the CMB temperature, leading to observable 21 cm emission at z<11.5.

The transition redshift from absorption to emission in 21 cm signals can constrain black hole accretion and feedback.

Abstract

In this paper we examine the effect of X-ray and Lyalpha photons on the intergalactic medium temperature. We calculate the photon production from a population of stars and micro-quasars in a set of cosmological hydrodynamic simulations which self-consistently follow the dark matter dynamics, radiative processes as well as star formation, black hole growth and associated feedback processes. We find that, (i) IGM heating is always dominated by X-rays unless the Lyalpha photon contribution from stars in objects with mass M<10^8 Msun becomes significantly enhanced with respect to the X-ray contribution from BHs in the same halo (which we do not directly model). (ii) Without overproducing the unresolved X-ray background, the gas temperature becomes larger than the CMB temperature, and thus an associated 21 cm signal should be expected in emission, at z<11.5. We discuss how in such a scenario the transition redshift between a 21 cm signal in absorption and in emission could be used to constraint BHs accretion and associated feedback processes.