In Search of the Full AGN Population
The fact that AGN viewing orientation effects its appearance, and thus its classification has long been evident from the variety of radio structures. This, along with mounting mounting evidence from other wavebands has led to a variety of proposed Unification schemes as
well as the realization that common survey techniques are heavily biased, particularly against optically obscured AGN. The powerful
combination of radio, X-ray and IR surveys in this era of Great Observatories, both on the ground and in space, facilitating a potentially
unbiased view of AGN, has discovered many new candidate AGN including: red AGN, X-ray bright optically-normal galaxies (XBONGs), Type 2
quasars, X-ray detected Extremely Red Objects (V/EROs) and more. Their relations to one another and to AGN as a whole are not yet clear, but
the richness and variety of their properties offers us an unprecedented opportunity to test AGN models, Unification schemes and advance our understanding of AGN structure both by studying the new samples, well-defined subsets or extreme source types.
Red AGN are a promising subset because they are dominated by intermediate class sources in which weakened AGN emission competes with components which are too weak to study in blue, type 1 AGN. Red AGN are generally a mixed bag of sources with various reasons for their red color and including at least a few extremely unusual sources.
The wide variety of their observed spectral energy distributions (SEDs) reveals that Eddington ratio is a primary factor, but with
contributions from intrinsic circumnuclear and host galaxy obscuration, scattered AGN light and host galaxy emission. The X-ray spectra are
complex, including a combination of direct and reflected emission with variable obscuration and a soft excess. Applying this SED modelling to the X-ray sources in a 0.6 sq.deg. Chandra survey in the SWIRE, Lockman Hole region clearly demonstrates the prevalance of red sources in X-ray samples and leads to strong support for alternative definitions of radio-loudness for the bulk of the AGN population which is not optically bright.
I will close with preliminary results from a Chandra survey of high-redshift 3CR sources aimed at tracing the angular dependence of AGN multi-wavelength properties where the viewing angle can be independently estimated from the radio structure.
