Does the AGN Unified Model Evolve with Redshift? Using the X-Ray Background to Predict the Mid-Infrared Emission of AGNs
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Deep X-ray surveys by Chandra and XMM-Newton have resolved about 80% of the 2-10 keV cosmic extragalactic X-ray background (CXRB) into point sources, the majority of which are obscured AGNs. The obscuration might be connected to processes within the host galaxy, possibly the star formation rate. Here we use the results of CXRB synthesis calculations as input to detailed CLOUDY simulations in order to predict the evolution of AGN properties at several mid-IR wavelengths. Computations were performed for three different evolutions of the AGN type 2/type 1 ratio betweenz = 0 and 1, where the ratio increased as (1 + z)0.9, as (1 + z)0.3, and with one model having no redshift evolution. Models were calculated with the inner radius of the absorbing gas and dust at 1 or at 10 pc. Comparing the results of the calculations to combined X-ray and Spitzer data of AGNs show that the predicted spectral energy distributions are a good description of average AGNs found in the deep surveys. The existing data indicate that the mid-IR emission from an average AGN is best described by models in which the attenuating material is 10 pc from the central engine. We present the expected Spitzer cumulative number count distributions and the evolution of the total AGN (type 1+type 2) luminosity function (LF) between z = 0 and 1 at rest frame 8 and 30 m for the three evolutionary scenarios. The mid-IR AGN LF will be an excellent tool to measure the evolution of the covering factor of the gas and dust from z 0 to 1. 2006. The American Astronomical Society. All righls reserved.
