Modification of cluster radio halo appearance by the thermal Sunyaev-Zeldovich effect

Abstract

We discuss the consequences of the spectral and morphological modification of galaxy cluster radio halos due to the Sunyaev-Zeldovich (SZ) effect for the interpretation of existing and upcoming high frequency radio observations. Likely these modifications have affected the interpretation of the existing Coma cluster radio data. The radio halo emission visible at low (< 5 GHz) frequencies is at higher (> 10 GHz) frequencies completely over-compensated by the thermal SZ decrement. Thus, the total radio emission of a galaxy cluster goes through zero (in comparison to the constant cosmic microwave background (CMB) emission) at a frequency of several GHz. Since the radio halo brightness has a narrow radial profile compared to the SZ decrement, a central emission region is surrounded by a decrement within the intermediate frequency range of several GHz. The size of this emission regions shrinks with increasing frequency until the decrement dominates everywhere in the cluster.