Determination of the hot intracluster gas temperature from submillimeter measurements

Abstract

Measurements of the Sunyaev-Zeldovich (hereafter SZ) distorsion of the cosmic microwave background can give interesting physical informations on clusters of galaxies, provided that the electronic temperature of the gas is known. Previous attempts to do so have used the electronic temperature determination obtained from the X-ray spectra. However, if the intergalactic gas is not homogeneous, the X-ray emission will trace the denser component, and the temperature determination may not be relevant for the lower density gas which is dominating the SZ measurements. Moreover, the X-ray brightness decreases very rapidly with the distance, which is not the case for the SZ effect. Distant clusters might be detected from SZ measurements, whereas they are inaccessible to X-ray observations. For these reasons, we have investigated the possibility to derive the electronic temperature of the gas from the SZ measurements in the submillimeter range (lambda ~ 300-600 micro-m). We show that given the sensitivities of the future submillimeter space missions Planck Surveyor and FIRST, the electronic temperature of massive clusters (Y_center=3*10^{-4}) can be determined with an accuracy ranging from 1 to 4 keV depending on its distance and the data avalaible.