SLAC-PUB-14355 Three years Swift–BAT Survey of AGN: reconciling theory and observations?∗ D. Burlon1,
[email protected] M. Ajello2,
[email protected] J. Greiner1, A. Comastri3, A. Merloni1,4, and N. Gehrels5 ABSTRACT It is well accepted that unabsorbed as well as absorbed AGN are needed to explain the nature and the shape of the Cosmic X-ray background, even if the fraction of highly absorbed objects (dubbed Compton-thick sources) substan- tially still escapes detection. We derive and analyze the absorption distribution using a complete sample of AGN detected by Swift–BAT in the first three years of the survey. The fraction of Compton-thick AGN represents only 4.6% of the total AGN population detected by Swift–BAT. However, we show that once cor- rected for the bias against the detection of very absorbed sources the real intrinsic +9 fraction of Compton-thick AGN is 20−6 %. We proved for the first time (also in the BAT band) that the anti-correlation of the fraction of absorbed AGN and luminosity it tightly connected to the different behavior of the luminosity func- tions (XLFs) of absorbed and unabsorbed AGN. This points towards a difference between the two subsamples of objects with absorbed AGN being, on average, 1Max-Planck-Institut f¨ur Extraterrestrische Physik, Giessenbachstraße 1, 85740 Garching, Germany 2SLAC National Laboratory and Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park, CA 94025, USA 3INAF Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy 4Excellence Cluster Universe, TUM, Boltzmannstraße 2, 85748, Garching, Germany 5Astrophysics Science Division, Mail Code 661, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA *Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.