We explore the connection between different classes of active galactic nuclei (AGNs) and the evolution of their host galaxies, by deriving host galaxy properties, clustering, and Eddington ratios of AGNs selected in the radio, X-ray, and infrared (IR) wavebands. We study a sample of 585 AGNs at 0.25 < z < 0.8 using redshifts from the AGN and Galaxy Evolution Survey (AGES). We select AGNs with observations in the radio at 1.4 GHz from the Westerbork Synthesis Radio Telescope, X-rays from the Chandra XBoötes Survey, and mid-IR from the Spitzer IRAC Shallow Survey. The radio, X-ray, and IR AGN samples show modest overlap, indicating that to the flux limits of the survey, they represent largely distinct classes of AGNs. We derive host galaxy colors and luminosities, as well as Eddington ratios, for obscured or optically faint AGNs. We also measure the two-point cross-correlation between AGNs and galaxies on scales of 0.3-10 h −1 Mpc, and derive typical dark matter halo masses. We find that: (1) radio AGNs are mainly found in luminous red sequence galaxies, are strongly clustered (with M halo ∼ 3 × 10 13 h −1 M ⊙ ), and have very low Eddington ratios (λ 10 −3 ); (2) X-rayselected AGNs are preferentially found in galaxies that lie in the "green valley" of color-magnitude space and are clustered similar to typical AGES galaxies (M halo ∼ 10 13 h −1 M ⊙ ), with 10 −3 λ 1; (3) IR AGNs reside in slightly bluer, slightly less luminous galaxies than X-ray AGNs, are weakly clustered (M halo 10 12 h −1 M ⊙ ), and have λ > 10 −2 . We interpret these results in terms of a simple model of AGN and galaxy evolution, whereby a "quasar" phase and the growth of the stellar bulge occurs when a galaxy's dark matter halo reaches a critical mass between ∼10 12 and 10 13 M ⊙ . After this event, star formation ceases and AGN accretion shifts from radiatively efficient (optical-and IR-bright) to radiatively inefficient (optically faint, radio-bright) modes.

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The XBoötes Survey is a 5-ks Chandra survey of the Boötes Field of the NOAO Deep Wide-Field Survey (NDWFS). This survey is unique in that it is the largest (9.3 deg 2 ), contiguous region imaged in X-ray with complementary deep optical and near-IR observations. We present a catalog of the optical counterparts to the 3,213 X-ray point sources detected in the XBoötes survey. Using a Bayesian identification scheme, we successfully identified optical counterparts for 98% of the X-ray point sources. The optical colors suggest that the optically detected galaxies are a combination of z <1 massive early-type galaxies and bluer star-forming galaxies whose optical AGN emission is faint or obscured, whereas the majority of the optically detected point sources are likely quasars over a large redshift range. Our large area, X-ray bright, optically deep survey enables us to select a large sub-sample of sources (773) with high X-ray to optical flux ratios (f x /f o >10). These objects are likely high redshift and/or dust obscured AGN. These sources have generally harder X-ray spectra than sources with 0.1

We obtained a 5 ksec deep Chandra X-ray Observatory ACIS-I map of the 9.3 square degree Boötes field of the NOAO Deep Wide-Field Survey. Here we describe the data acquisition and analysis strategies leading to a catalog of 4642 (3293) point sources with 2 or more (4 or more) counts, corresponding to a limiting flux of roughly 4(8) × 10 −15 erg cm −2 s −1 in the 0.5-7 keV band. These Chandra XBoötes data are unique in that they consitute the widest contiguous X-ray field yet observed to such a faint flux limit. Because of the extraordinarily low background of the ACIS, we expect only 14% (0.7%) of the sources to be spurious. We also detected 43 extended sources in this survey. The distribution of the point sources among the 126 pointings (ACIS-I has a 16 x 16 arcminute field of view) is consistent with Poisson fluctuations about the mean of 36.8 sources per pointing. While a smoothed image of the point source distribution is clumpy, there is no statistically significant evidence of large scale filamentary structure. We do find however, that for θ > 1 arcminute, the angular correlation function of these sources is consistent with previous measurements, following a power law in angle with slope ∼ −0.7. In a 1.4 deg 2 sample of the survey, approximately 87% of the sources with 4 or more counts have an optical counterpart to R∼ 26 -2mag. As part of a larger program of optical spectroscopy of the NDWFS Boötes area, spectra have been obtained for ∼ 900 of the X-ray sources, most of which are QSOs or AGN.

We present one of the most precise measurement to date of the spatial clustering of X-ray selected AGNs using a sample derived from the Chandra X-ray Observatory survey in the Boötes field. The real-space twopoint correlation function over a redshift interval from z = 0.17 to z ∼ 3 is well described by the power law, ξ(r) = (r/r 0 ) −γ , for comoving separations r 20 h −1 Mpc. We find γ = 1.84 ± 0.12 and r 0 consistent with no redshift trend within the sample (varying between r 0 = 5.5 ± 0.6 h −1 Mpc for z = 0.37 and r 0 = 6.9 ± 1.0 h −1 Mpc for z = 1.28). Further, we are able to measure the projections of the two-point correlation function both on the sky plane and in the line of sight. We use these measurements to show that the Chandra/Boötes AGNs are predominantly located at the centers of dark matter halos with the circular velocity v max > 320 km s −1 or M 180 > 4.1 × 10 12 h −1 M , and tend to avoid satellite galaxies in halos of this or higher mass. The halo occupation properties inferred from the clustering properties of Chandra/Boötes AGNs -the mass scale of the parent dark matter halos, the lack of significant redshift evolution of the clustering length, and the low satellite fraction -are broadly consistent with the Hopkins et al. (2006) scenario of quasar activity triggered by mergers of similarly-sized galaxies.