Effect of the non-thermal Sunyaev–Zel’dovich effect on the temperature determination of galaxy clusters

Marchegiani, P.
Colafrancesco, S.
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Oxford University Press (OUP)
A recent stacking analysis of Planck HFI data of galaxy clusters led to the derivation of the cluster temperatures using the relativistic corrections to the Sunyaev-Zel'dovich effect (SZE). However, the temperatures of high-temperature clusters, as derived from this analysis, were basically higher than the temperatures derived from X-ray measurements, at a moderate statistical significance of 1.5 sigma. This discrepancy has been attributed by Hurier to calibration issues. In this paper, we discuss an alternative explanation for this discrepancy in terms of a non-thermal SZE astrophysical component. We find that this explanation can work if non-thermal electrons in galaxy clusters have a low minimum momentum (p(1) similar to 0.5-1), and if their pressure is of the order of 20-30 per cent of the thermal gas pressure. Both these conditions are hard to obtain if the non-thermal electrons are mixed with the hot gas in the intracluster medium, but can be possibly obtained if the non-thermal electrons are mainly confined in bubbles with a high amount of non-thermal plasma and a low amount of thermal plasma, or are in giant radio lobes/relics in the outskirts of the clusters. To derive more precise results on the properties of the non-thermal electrons in clusters, and in view of more solid detections of a discrepancy between X-ray- and SZE-derived cluster temperatures that cannot be explained in other ways, it would be necessary to reproduce the full analysis done by Hurier by systematically adding the non-thermal component of the SZE.
Galaxies: clusters: general , Galaxies: clusters: intracluster medium , Cosmic background radiation , RADIO-EMISSION , PLASMA , SHOCKS , MATTER
Marchegiani, P. and Colafrancesco, S. 2017. Effect of the non-thermal Sunyaev–Zel’dovich effect on the temperature determination of galaxy clusters. Monthly Notices of the Royal Astronomical Society, 469(4), pp.4644-4648.