The thermal Sunyaev–Zeldovich effect of primordial recombination radiation

Abstract

It is well known that recombination radiation of primordial hydrogen-helium plasma leads to the distortions of the planckian spectrum shape of the cosmic microwave background radiation (CMB). We discuss the thermal Sunyaev-Zeldovich (SZ) effect with taking into account primordial recombination radiation (PRR). Since in the thermal SZ effect the redistribution of the photons depends on the derivatives of the spectrum, the value of relative correction to SZ effect due to PRR significantly higher than relative corrections due to PRR in the initial spectrum. Calculations of corrections to the thermal SZ effect due to PRR show that depending on the cluster parameters: 1) in the range of frequencies $\nu$ = 0.3 - 700 GHz where the cosmic microwave background (CMB) dominates and spectrum is very close to the planckian one the relative corrections due to PRR have an order of $10^{-9} - 10^{-6}$ of "pure" SZ effect (i.e. SZ effect for pure planckian spectrum). The difference of intensities of PRR coming from different directions (through intracluster and near intercluster medium) reaches values up to 22 mJy/ster at $\nu\simeq 337$ GHz (maximum in considered range). 2) In the range of frequencies $\nu$ = 700 - 5000 GHz where cosmic infrared background (CIB) becomes significant or even dominates the relative corrections due to PRR can reach $10^{-8}$ - $10^{-5}$ of "pure" SZ effect. Corresponding intensity difference reaches values up to 25 mJy/ster (at $\nu\simeq 1700$ GHz). In addition we suggest a modification of the method of electron gas temperature determination using corrections of the SZ effect due to PRR. Such modification allows one to simplify the determination of the cluster electron gas temperature in comparison with known methods.