Scientific Seminars

A Census of the AGN population in the SWIRE/Chandra Survey

Mari Polletta
University of California

2006-03-22    14:00    Brera -

The high sensitivity and spatial resolution of the Spitzer Space Telescope and of the Chandra X-ray Observatory provide a unique opportunity to investigate the properties of large samples of Active Galactic Nuclei (AGN) over large cosmic volumes. We present a census of the AGN population in the Chandra/SWIRE survey. The survey, part of the Spitzer Wide-Area InfraRed Extragalactic (SWIRE) Survey Legacy Project, covers a 0.6 square degrees field in the northern Lockman Hole SWIRE field and combines medium-depth X-ray data from Chandra, deep infrared data in all seven Spitzer bands, deep optical data from KPNO, and extremely deep VLA 20cm. We use this rich multi-wavelength dataset to identify three independent samples of AGN, based on their X-ray, radio and infrared properties. Once the selection effects of each method are taken into account, an unbiased view of all AGN in the field can be derived. We estimate that more than 60% of AGN are missed by the three selection methods. The spectral energy distributions (SEDs), luminosities, redshifts of each AGN sample are discussed. The optical and infrared SEDs of the identified AGN show a wide variety of shapes, with about 70% being similar to normal and starburst galaxies, and only 30% being characterized by AGN-like SEDs. Our results are compared to models for the joint properties of deep IR and X-ray selected AGN samples. A comparison between the estimated surface density of AGN detected in the Spitzer bands with predictions from those models shows a large disagreement among the models themselves and with the mid-infrared observations. The implications of our results are discussed in the context of AGN evolutionary models.