Spectral Energy Distributions of Type 1 AGNs

The spectral energy distributions (SEDs) of active galactic nuclei (AGNs) are essential to understand the physics of supermassive black holes (SMBHs) and their host galaxies. This thesis present a detailed study of AGN SED shapes in the optical-near infrared bands (0.3--3microm) for 413 X-ray selected Type 1 AGNs from the XMM-COSMOS Survey. We define a useful near-IR/optical index-index ('color-color') diagram to investigate the mixture of AGN continuum, host galaxy and reddening contributions.;We found that ∼90% of the AGNs lie on mixing curves between the Elvis et al. (1994) mean AGN SED (E94) and a host galaxy, with only the modest reddening [E(B-V)=0.1--0.2] expected in type 1 AGNs. Lower luminosity and Eddington ratio objects have more host galaxy, as expected. The E94 template is remarkably good in describing the SED shape in the 0.3--3microrn decade of the spectrum over a range of 3.2 dex in LOPT, 2.7 dex in L/LEdd, and for redshifts up to 3. The AGN phenomenon is thus insensitive to absolute or relative accretion rate and to cosmic time.;However, 10% of the AGNs are inconsistent with any AGN+host+reddening mix. These AGNs have weak or non-existent near-IR bumps, suggesting a lack of the hot dust characteristic of AGNs. The fraction of these hot-dust-poor AGNs evolves with redshift from 6% at low redshift (z < 2) to 20% at moderately high redshift (2 < z < 3.5). A similar fraction of HDP quasars are found in the Elvis et al. 1994 (BQS) and Richards et al. 2006 (SDSS) samples.;The 1--3microm emission of the HDP quasars is a factor 2--4 smaller than the typical E94 AGN SED. The implied torus covering factor is 2%--29%, well below the 75% required by unified models. The weak hot dust emission seems to expose an extension of the accretion disk continuum in some of AGNs. For these, we estimate the outer edge of their accretion disks to lie at ∼104 Schwarzschild radii, more than ten times the gravitational stability radii. Either the host-dust is destroyed (dynamically or by radiation), or is offset from the central black hole due to recoiling. Alternatively, the universality of HDP quasars in samples with different selection methods and the continuous distribution of dust covering factor in type 1 AGNs, suggest that the range of SEDs could be related to the range of tilts in warped fueling disks, as in the model of Lawrence and Elvis (2010), with HDP quasars having relatively small warps.;A small number of other outliers are found with the help of the mixing diagram, which could represent quasars on different evolutionary stage. The proposed 'cosmic cycle' (Hopkins et al. 2006) of SMBH and galaxy co-evolution can be shown as tracks on the mixing diagram.