Dust emission from clusters of galaxies: statistical detection

Centre d'Études Spatiales des Rayonnements, 9 avenue Colonel Roche, 31022 Toulouse, France e-mail: montier@cesr.fr

Received: 18 November 2004
Accepted: 3 March 2005

Abstract

The detection of the IR emission from individual galaxy clusters is a difficult task due to the extremely low level of this emission and the fluctuations of the IR sky, galactic cirrus and background galaxies. We have statistically detected a significant IR emission toward galaxy clusters at , , and by co-adding the IRAS maps toward a total of 11 507 galaxy clusters extracted from the CDS database. This process averages the sky fluctuations of the astrophysical sky and the survey noise to a very low level in all four bands. We have obtained an averaged central detection at all wavelengths, with an intensity of , , and respectively. These detections have been confirmed against possible spurious or systematic signals using different test methods. The origin of this detected IR emission is discussed. The free-free contribution to the IR emission can be ruled out. Both the level of the emission and its spectrum favor an interpretation in terms of dust emission. However the exact location of this dust remains unknown: is this emission due to intergalactic dust, or simply the dust included in the galaxies of the clusters? This last question will be discussed in a forthcoming paper.