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The near-infrared radiation background, gravitational wave background and star formation rate of Pop III and Pop II during cosmic reionization

In this paper, we obtain the NIRB and SBGWs from the early stars, which are constrained by the observation of reionization and star formation rate. We study the transition from Pop III to Pop II stars via the star formation model of different population, which takes into account the reionization and the metal enrichment evolution. We calculate the two main metal pollution channels arising from the supernova-driven protogalactic outflows and "genetic channel". We obtain the SFRs of Pop III and Pop II and their NIRB and SBGWs radiation. We predict that the upper limit of metallicity in metal-enriched IGM (the galaxies whose polluted via "genetic channel") reaches $Z_{\rm crit}=10^{-3.5}Z_{\odot}$ at $z\sim13$ ($z\sim11$), which is consistent with our star formation model. We constrain on the SFR of Pop III stars from the observation of reionization. The peak intensity of NIRB is about $0.03-0.2~nW m^{-2}{sr}^{-1}$ at $\sim 1 μm$ for $z>6$. The prediction of NIRB signal is consistent with the metallicity evolution. We also obtain the gravitational wave background from the black holes formed by these early stars. The predicted gravitational wave background has a peak amplitude of $Ω_{GW}\simeq8\times10^{-9}$ at $ν=158$ Hz for Pop II star remnants. However, the background generated by Pop III.2 stars is much less than Pop II stars, with a peak amplitude of $Ω_{GW}\simeq1.2\times10^{-11}$ at $ν=28~Hz$. The background of Pop III.1 shifts to lower frequencies, and the amplitude of $Ω_{GW}$ for Pop III.1 stars shows a minimum value at $ν\simeq 10$ Hz, due to the lack of gravitational wave signals from the stars with $140~M_{\odot}<M_\ast<260~M_{\odot}$.