Studying the leptonic structure of galaxy cluster atmospheres from the spectral properties of the SZ effect

TL;DR

This paper analyzes the spectral properties of the Sunyaev-Zel'dovich effect around the crossover frequency to distinguish between thermal and non-thermal electron populations in galaxy cluster atmospheres, proposing a method to obtain unbiased electron distribution information.

Contribution

It provides analytical expressions for the crossover frequency and spectral slope of the SZE for different electron populations, highlighting the slope's robustness against kinematic effects.

Findings

Crossover frequency depends on cluster velocity V_r.

Spectral slope is unaffected by kinematic SZE in the optimal frequency range.

Spectral slope measurements can reveal electron distribution properties.

Abstract

We study the energetics of galaxy cluster atmospheres by analyzing the SZ effect spectra around the crossover frequency. We calculated analytically the expressions of both the crossover frequency and the spectral slope of the SZE around the crossover frequency in various cases: a thermal electron population; a power-law, non-thermal electron population; and a population of electrons experiencing a stochastic acceleration. We find that the value of the crossover frequency X_0 of the SZE depends significantly on the cluster peculiar velocity V_r (which determines the amplitude of the kinematic SZE), while the value of the slope of the SZE does not depend on the kinematic SZE spectrum in the optimal frequency range around the crossover frequency of the thermal SZE, i.e. in the (a-dimensional) frequency range x = 3.5 - 4.5. Thus, while the amplitude of the kinematic SZE produces a systematic bias in the position of the crossover frequency, it does not affect significantly the spectral slope of the SZE. We therefore propose to use measurements of the spectral slope of the SZE to obtain unbiased information about the specific properties of various electron distributions in galaxy clusters as well as in other cosmic structures in which a SZE can be produced.