A Serendipitous XMM Survey of the SDSS: the evolution of the colour-magnitude diagram of X-ray AGN from z=0.8 to z=0.1

Abstract

A new serendipitous XMM survey in the area of the Sloan Digital Sky Survey is described (XMM/SDSS), which includes features such as the merging of overlapping fields to increase the sensitivity to faint sources, the use of a new parametrisation of the XMM point spread function for the source detection and photometry, the accurate estimation of the survey sensitivity. About 40,000 X-ray point sources are detected over a total area of 122deg2. A subsample of 209 sources detected in the 2-8keV spectral band with SDSS spectroscopic redshifts in the range 0.03<z<0.2, optical magnitudes r<17.77mag and logLx(2-10keV)>41.5 (erg/s) are selected to explore their distribution on the colour magnitude diagram. This is compared with the colour-magnitude diagram of X-ray AGN in the AEGIS field at z~0.8. We find no evidence for evolution of the rest-frame colours of X-ray AGN hosts from z=0.8 to z=0.1. This suggests that the dominant accretion mode of the AGN population, which is expected to imprint on the properties of their host galaxies, does not change since z=0.8. This argues against scenarios which attribute the rapid decline of the accretion power of the Universe with time (1dex since z=0.8) to changes in the AGN fueling/triggering mode.