Quasar SEDs in XMM-COSMOS: 90% Uniform, 10% Hot-Dust-Poor - Low Covering Factors and Large Accretion Disk Outer Radii

Details Quasar SEDs in XMM-COSMOS: 90% Uniform, 10% Hot-Dust-Poor - Low Covering Factors and Large Accretion Disk Outer Radii Quasar SEDs in XMM-COSMOS: 90% Uniform, 10% Hot-Dust-Poor - Low Covering Factors and Large Accretion Disk Outer Radii

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21712504h&link_type=abstract

American Astronomical Society, AAS Meeting #217, #125.04; Bulletin of the American Astronomical Society, Vol. 43, 2011

Physics

Scientific paper

The spectral energy distributions (SEDs) of AGNs are essential to understand the physics of the supermassive black holes (SMBHs) and their host galaxies. We present a detailed study of AGN SED shapes in the optical-near infrared for 408 X-ray selected type 1 AGNs from the XMM-COSMOS Survey. We define an near-IR/optical index-index ('color-color') diagram to investigate the mixture of AGN continuum, reddening and host galaxy contribution.
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]. Lower luminosity and Eddington ratio objects have more host galaxy. The E94 is remarkably good in describing the SED shape in the 0.3-3 micron decade over a range of 3.2 dex in Lopt, 2.7 dex in L/LEdd, and for redshifts up to 3.
However, 10% of the AGNs are inconsistent with any AGN+host+reddening mix. These AGNs have weak or non-exist 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 z<2 to 20% at 2The 1-3micron emission 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. We estimate the outer edge of their accretion disks to lie at 104 Schwarzschild radii, more than ten times the gravitational stability radii. These 'hot-dust-poor' quasars may have 'tori' disrupted by mergers or may be recoiling black holes.

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