ASCA OBSERVATIONS OF DEEP ROSAT FIELDS - II - THE 2-10KEV AGN LUMINOSITY FUNCTION

We present additional optical spectroscopic identifications of sources identified in three deep ASCA GIS fields which also form part of a de ep ROSAT survey. in total, 26 ASCA sources have been detected down to a 2-10keV flux limit of S2-10 = 5 X 10(-14) erg cm(-2) s(-1). Low Disp ersion Survey Spectrograph observations have increased the spectroscop ic completeness of the survey to between 65 and 85 per cent, with iden tifications for up to 13 QSOs with broad emission lines and six object s with narrow emission lines. Combining these objects with the AGN ide ntified in the HEAO A-1 sample by Grossan, we find evidence for signif icant cosmological evolution in the 2-10 keV band ((V-e/V-a) = 0.63 +/ - 0.03), fitted by a pure luminosity evolution model: L proportional t o (1 + z)(k), k = 2.04(-0.22)(+0.16). The present-epoch 2-10 keV AGN X -ray luminosity function, Phi(L-X), is best represented by a two-power -law function: Phi(L-X) proportional to L-3.0, L > 10(44.1) erg s(-1) ; Phi(L-X) proportional to L-1.9, L < 10(44.1) erg s(-1). Depending o n the extent to which we extrapolate the z = 0 AGN luminosity function , we predict a total contribution to the 2-10 keV X-ray background fro m QSOs and narrow-emission-line galaxies which ranges from 48 per cent (for AGN with L-X > 10(42) erg s(-1)) to 80 per cent(L-X > 10(39) erg s(-1)).