Heating and Ionization of the Primordial Intergalactic Medium by High Mass X-ray Binaries

TL;DR

This study models how High Mass X-ray Binaries influence the ionization and temperature of the early intergalactic medium, finding they have limited impact on reionization but can sustain partial ionization and cooling.

Contribution

It provides the first detailed radiative transfer simulations of HMXBs' effects on high-redshift environments considering different density profiles.

Findings

HMXBs produce negligible ionization in uniform density environments.

HMXBs help maintain partial ionization behind recombination fronts in NFW halos.

X-ray escape fractions are high, potentially affecting distant IGM over time.

Abstract

We investigate the influence of High Mass X-ray Binaries on their high redshift environments. Using a one-dimensional radiative transfer code, we predict the ionization and temperature profiles surrounding a coeval stellar population, composed of main sequence stars and HMXBs, at various times after its formation. We consider both uniform density surroundings, and a cluster embedded in a 10^8 solar mass NFW halo. HMXBs in a constant density environment produce negligible enhanced ionization because of their high-energy SEDs and short lifetimes. In this case, HMXBs only marginally contribute to the local heating rate. For NFW profiles, radiation from main sequence stars cannot prevent the initially ionized volume from recombining since it is unable to penetrate the high density galactic core. However, HMXB photons stall recombinations behind the front, keeping it partially ionized for longer. The increased electron density in these partially ionized regions promotes further cooling, resulting in lower IGM temperatures. In the context of this starburst model, we have shown that HMXBs do not make a major contribution to reionization or IGM heating. However, X-ray escape fractions are high in both density profile cases. Continuous star formation may result in the build up of X-rays over time, reducing the ionization timescale and potentially leading to low level ionization of the distant IGM.