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A Clash of Clusters Provides New Clue to Dark Matter
Special ACKS Seminar: Dragan Huterer
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ACKS Seminar: Belinda Wilkes (Chandra X-ray Center,Smithsonian Astrophysical Observatory)
| What | seminar ACKS |
|---|---|
| When |
25 October 06 from 10:00 am to 11:00 am |
| Where | SLAC FKB 2nd Floor Conference Room |
| Contact Name | Kirk Gilmore |
| Contact Email | dkg@slac.stanford.edu |
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An Unobscured View of the Quasar Population with Chandra and Spitzer
Abstract
The powerful combination of X-ray and Infrared (IR) surveys to study the Active Galaxies (AGN) population relatively unaffected by bias due to obscuration in the optical and soft-X-ray is proving successful in discovering, along with more normal AGN, unusual ones that make up a significant fraction of the population. As well as the type 2 AGN and quasars expected from models of the Cosmic X-ray Background (CXRB), the sources include other varieties: X-ray bright, normal galaxies (XBONGS), red, broad-lined AGN and low-luminosity AGN. Numbers of known sources remain sufficiently small that the relative importance of the various types remains to be determined and their potential to provide information on the geometry of AGN and to probe the obscuring material responsible for their unusual properties is yet to be realised. We need large area, relatively deep surveys to obtain sufficiently large samples to quantify their relative importance.
I summarise the AGN samples resulting from three X-ray and/or IR surveys: SWIRE/Chandra, ChaMP and 2MASS. The ChaMP X-ray sample, including 5500 sources in 9.6 sq. degs., provides the best determined X-ray logN vs logS to date and concludes that ~80% of the 0.2-8 keV CXRB is resolved by current surveys. Multi-wavelength studies reveal subsets of AGN which are obscured by material with column densities ranging from 22 < log N_H < 24, with a few being Compton thick. The observed spectral energy distributions (SEDs) of the red AGN can be explained by combining an unobscured AGN SED with both emission and obscuration from the host galaxy, plus polarised AGN emission in the optical/IR and a combination of direct and reflected emission with variable obscuration and a soft excess in the X-ray. These are all components known to be present in the emission from nearby, Seyfert galaxies. Obscuration allows galaxy, reflected and scattered components to contribute significantly to the emission in these higher luminosity AGN. But the extent to which they are also present in higher redshift and luminosity quasars remains a question.
KIPAC tea talk, Speaker: Gary Godfrey
Powerpoint presentation
Powerpoint presentation available here:
http://kipac.stanford.edu/collab/seminars/acks/06Fall/2006Oct25_BelindaWilkes.ppt/view