Using UV luminosity functions, CMB reionization data, quasar absorption, and the soft X-ray background, the authors set upper limits on Pop-III star formation and show that the global 21-cm signal has a region uniquely accessible if Pop-III stars exist.
The nature of the unresolved extragalactic soft CXB
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abstract
In this paper we investigate the power spectrum of the unresolved 0.5-2 keV CXB with deep Chandra 4 Ms observations in the CDFS. We measured a signal which, on scales >30", is significantly higher than the Shot-Noise and is increasing with the angular scale. We interpreted this signal as the joint contribution of clustered undetected sources like AGN, Galaxies and Inter-Galactic-Medium (IGM). The power of unresolved cosmic sources fluctuations accounts for \sim 12% of the 0.5-2 keV extragalactic CXB. Overall, our modeling predicts that \sim 20% of the unresolved CXB flux is made by low luminosity AGN, \sim 25% by galaxies and \sim 55% by the IGM (Inter Galactic Medium). We do not find any direct evidence of the so called Warm Hot Intergalactic Medium (i.e. matter with 10^5K<T<10^7K and density contrast {\delta} <1000), but we estimated that it could produce about 1/7 of the unresolved CXB. We placed an upper limit to the space density of postulated X-ray-emitting early black hole at z>7.5 and compared it with SMBH evolution models.
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Closing in on Pop-III Stars: Constraints and Predictions Across the Spectrum
Using UV luminosity functions, CMB reionization data, quasar absorption, and the soft X-ray background, the authors set upper limits on Pop-III star formation and show that the global 21-cm signal has a region uniquely accessible if Pop-III stars exist.