Finding rare AGN: XMM-Newton and Chandra observations of SDSS Stripe 82
Nandra, Kirpal; Schawinski, Kevin; Comastri, Andrea; Stern, Daniel; Urry, C. Megan; Murray, Stephen S.; Cappelluti, Nico; Treister, Ezequiel; Green, Paul; Böhringer, Hans; Chon, Gayoung; Glikman, Eilat; Civano, Francesca; LaMassa, Stephanie M.; Ranalli, Piero; Richards, Gordon; Ballantyne, David; Cardamone, Carie
United States, Italy, Greece, Chile, Switzerland, Germany
Abstract
We have analysed the XMM-Newton and Chandra data overlapping ∼16.5 deg2 of Sloan Digital Sky Survey Stripe 82, including ∼4.6 deg2 of proprietary XMM-Newton data that we present here. In total, 3362 unique X-ray sources are detected at high significance. We derive the XMM-Newton number counts and compare them with our previously reported Chandra logN-logS relations and other X-ray surveys. The Stripe 82 X-ray source lists have been matched to multiwavelength catalogues using a maximum likelihood estimator algorithm. We discovered the highest redshift (z = 5.86) quasar yet identified in an X-ray survey. We find 2.5 times more high-luminosity (Lx ≥ 1045 erg s-1) AGN than the smaller area Chandra and XMM-Newton survey of COSMOS and 1.3 times as many identified by XBoötes. Comparing the high-luminosity active galactic nuclei (AGN) we have identified with those predicted by population synthesis models, our results suggest that this AGN population is a more important component of cosmic black hole growth than previously appreciated. Approximately a third of the X-ray sources not detected in the optical are identified in the infrared, making them candidates for the elusive population of obscured high-luminosity AGN in the early universe.