THE LUMINOSITY FUNCTION EVOLUTION OF SOFT X-RAY-SELECTED ACTIVE GALACTIC NUCLEI IN THE RIXOS SURVEY

A sample of 198 soft X-ray-selected active galactic nuclei (AGN) from the ROSAT International X-ray Optical Survey (RIXOS) is used to invest igate the X-ray luminosity function and its evolution. RIXOS, with a f lux limit of 3 x 10(-14) erg s(-1) cm(-2) (0.5 to 2.0 keV), samples a broad range in redshift over 20 deg(2) of sky, and is almost completel y identified; it is used in combination wtih the Einstein Extended Med ium Sensitivity Survey (EMSS) to give a total sample of over 600 AGN. We find the evolution of AGN with redshift to be consistent with pure luminosity evolution (PLE) models in which the evolution slows markedl y or stops at high redshifts (z > 1.8). We find that this result is no t affected by the inclusion, or exclusion, of narrow-emission-line gal axies at low redshift in the RIXOS and EMSS samples, and is insensitiv e to uncertainties in the conversion between flux values measured with ROSAT and Einstein. We confirm, using a model-independent [V-e/V-a] t est, that our survey is consistent with no evolution at high redshifts .