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

Free access article

Issue		A&A Volume 396, Number 2, December III 2002


Page(s)		L17 - L20
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20021613

A&A 396, L17-L20 (2002)
DOI: 10.1051/0004-6361:20021613

Letter

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

T. A. Enßlin

Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str.1, Postfach 1317, 85741 Garching, Germany
(Received 11 October 2002 / Accepted 31 October 2002 )

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 ( $\la$ 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.

Key words: intergalactic medium -- galaxies: cluster: general -- radio continuum: general -- radiation mechanism: thermal -- radiation mechanism: non-thermal -- cosmic microwave background

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