Speaker
Description
Recently, the Hydrogen Epoch of Reionization Array (HERA) has placed upper bounds on the cosmological 21-cm power spectrum at redshifts $\approx8$ and $10$. These bounds have been instrumental in constraining $L_{\rm X<2 \, keV}/{\rm SFR}$, the soft-band X-ray luminosity per unit star formation rate (SFR). Results suggest that values below $\approx 10^{39.5}\, {\rm erg} \;{\rm s}^{-1} \;{\rm M}_{\odot}^{-1} \;{\rm yr}$ are strongly disfavored. This assessment stems from analyzing semi-numerical models of the 21-cm signal which considers contributions only from atomic cooling galaxies hosting PopII stars. In this study, we reproduce these bounds on $L_{\rm X<2 \, keV}/{\rm SFR}$ and other relevant parameters by incorporating molecular cooling galaxies hosting PopIII stars into the simulation of the cosmic dawn 21-cm signal. We demonstrate that with the inclusion of molecular cooling galaxies, the lower values of $L_{\rm X<2 \, keV}/{\rm SFR}$ are no longer strongly disfavored. Consequently, this suggests that high-redshift X-ray sources may not necessarily need to exhibit significantly higher X-ray luminosity than high-mass X-ray binaries observed at lower redshifts.
