XMM-Newton Surveys of the CFRS Fields - I: The Sub-mm/X-ray relation

Abstract

First results from XMM-Newton observations of the Canada France Redshift Survey (CFRS) 3hr, 10hr and 14hr fields are presented. Limited regions of two of the XMM surveys (3 and 14hr) are compared to the Canada UK Deep sub-mm Surveys (CUDSS) undertaken with SCUBA. None of the 27 SCUBA sources in the 3hr field are detected by XMM, while one of the 23 SCUBA sources in the 14hr field is found to coincide with an X-ray source. The SCUBA population as a whole is not significantly detected in either the 0.5-2 keV or the 2-10 keV X-ray bands, even after coadding the X-ray flux at the SCUBA positions, in both fields. The 18 X-ray sources within the CUDSS 3hr map yield a mean sub-mm flux of 0.48+-0.27 mJy after coadding the sub-mm flux at the X-ray positions. Using this result we place an upper limit on the contribution of AGN to the sub-mm background at 850 microns of ~7 per cent. Conversely we estimate the contribution of sub-mm sources to the 0.5-2 keV X-ray background to be <16.5 per cent. These results strongly support the conclusion that the two backgrounds are caused by different processes, in the one case nucleosynthesis in stars, in the other accretion onto black-holes. We conclude that it is possible for SCUBA sources in general to contain AGN, as long as they are Compton-thick and are at z>2.3. The ratio of the X-ray to sub-mm flux for the X-ray sources however, implies that even when a galaxy does contain an AGN, most of the energy heating the dust is from young stars and not from the active nucleus.