Spectral Energy Distributions of Hard X-Ray Selected Active Galactic Nuclei in the XMM-Newton Medium Deep Survey

July 2007 • 2007ApJ...663...81P

Authors • Polletta, M. • Tajer, M. • Maraschi, L. • Trinchieri, G. • Lonsdale, C. J. • Chiappetti, L. • Andreon, S. • Pierre, M. • Le Fèvre, O. • Zamorani, G. • Maccagni, D. • Garcet, O. • Surdej, J. • Franceschini, A. • Alloin, D. • Shupe, D. L. • Surace, J. A. • Fang, F. • Rowan-Robinson, M. • Smith, H. E. • Tresse, L.

Abstract • We present the SEDs of a hard X-ray selected sample containing 136 sources with F_2-10keV>10^-14 erg cm^-2 s^-1 132 are AGNs. The sources are detected in a 1 deg² area of the XMM-Newton Medium Deep Survey where optical data from the VVDS and CFHTLS and infrared data from the SWIRE survey are available. Based on a SED fitting technique we derive photometric redshifts with σ(1+z)=0.11 and 6% of outliers and identify AGN signatures in 83% of the objects. This fraction is higher than derived when a spectroscopic classification is available. The remaining 17⁺⁹_-6% of AGNs show star-forming galaxy SEDs (SF class). The sources with AGN signatures are divided in two classes, AGN1 (33⁺⁶_-1%) and AGN2 (50⁺⁶_-11%). The AGN1 and AGN2 classes include sources whose SEDs are fitted by type 1 and type 2 AGN templates, respectively. On average, AGN1s show soft X-ray spectra, consistent with being unabsorbed, while AGN2s and SFs show hard X-ray spectra, consistent with being absorbed. The analysis of the average SEDs as a function of X-ray luminosity shows a reddening of the infrared SEDs, consistent with a decreasing contribution from the host galaxy at higher luminosities. The AGNs in the SF classes are likely obscured in the mid-infrared, as suggested by their low L_3-20μm/L^corr_0.5-10keV ratios. We confirm the previously found correlation for AGNs between the radio luminosity and the X-ray and the mid-infrared luminosities. The X-ray-radio correlation can be used to identify heavily absorbed AGNs. However, the estimated radio fluxes for the missing AGN population responsible for the bulk of the background at E>10 keV are too faint to be detected even in the deepest current radio surveys.

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Dave Shupe

Senior Scientist