SZ effect from radio-galaxy lobes: astrophysical and cosmological relevance

Abstract

ABSTRACT We derive the SZ effect arising in radio-galaxy lobes that are filled with high-energy,non-thermal electrons. We provide here quantitative estimates for SZ effect expectedfrom the radio galaxy lobes by normalizing it to the Inverse-Compton light, observedin the X-ray band, as produced by the extrapolation to low energies of the radioemitting electron spectrum in these radio lobes. We compute the spectral and spa-tial characteristics of the SZ effect associated to the radio lobes of two distant radiogalaxies (3C294 and 3C432) recently observed by Chandra, and we further discussits detectability with the next generation microwave and sub-mm experiments witharcsec and ∼ µK sensitivity. We finally highlight the potential use of the SZE fromradio-galaxy lobes in the astrophysical and cosmological context.Key words: Active galactic nuclei – SZ: cosmology – theory. 1 INTRODUCTIONThe Sunyaev-Zel’dovich effect (hereafter SZE, Sunyaev &Zel’dovich 1972, 1980) is a powerful probe of the physicalconditions of electronic plasmas in astrophysical and cosmo-logical context (see Birkinshaw 1999 for a review). A SZEcan be produced by thermal (hot and/or warm) electrons inthe atmospheres of galaxies and galaxy clusters (Birkinshaw1999, Itoh et al. 1998, Colafrancesco et al. 2003), by non-thermal (and relativistic) electrons in clusters and in thecavities produced by AGN radio lobes (Ensslin & Kaiser2000, Colafrancesco et al. 2003, Colafrancesco 2005) and bythe secondary electrons produced by Dark Matter annihila-tion in cosmic structures (Colafrancesco 2004), beyond thekinematic SZE related to the bulk motion of such plasmas.A SZE from the lobes of radio galaxies is also expected (En-sslin & Kaiser 2000, Colafrancesco et al. 2003, Blundell etal. 2006, Colafrancesco 2005, 2007) but it has not been de-tected yet. Nonetheless, several indirect limits can be set tothe SZE from radio-galaxy lobes using both the availableradio and X-ray information of these structures.In fact, detailed studies of radio-galaxy lobes (e.g.,Brunetti et al. 2002, Harris & Krawczynski 2002, Kataokaet al. 2003, Croston et al. 2005, Blundell et al. 2006 end ref-erences therein) have shown that these extended structurescontain electrons that have passed through the inner jets andthe hotspots and are diffusing on larger-scale lobes where