HERA bound on x-ray luminosity when accounting for population III stars
arXiv:2307.15577
Abstract
Recent upper bounds from the Hydrogen Epoch of Reionization Array (HERA) on the cosmological 21-cm power spectrum at redshifts , have been used to constrain , the soft-band X-ray luminosity measured per unit star formation rate (SFR), strongly disfavoring values lower than . This conclusion is derived from semi-numerical models of the 21-cm signal, specifically focusing on contributions from atomic cooling galaxies that host PopII stars. In this work, we first reproduce the bounds on and other parameters using a pipeline that combines machine learning emulators for the power spectra and the intergalactic medium characteristics, together with a standard Markov chain Monte Carlo parameter fit. We then use this approach when including molecular cooling galaxies that host PopIII stars in the cosmic dawn 21-cm signal, and show that lower values of are hence no longer strongly disfavored. The revised HERA bound does not require high-redshift X-ray sources to be significantly more luminous than high-mass X-ray binaries observed at low redshift.
22 pages, 13 figures, 2 tables. Version accepted for publication in PRD