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OATS-DAUT SEMINAR
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Speaker:
Maria Polletta (Institut d'Astrophysique de Paris)
Title:
Active Galactic Nuclei in the infrared: identification, energetic
and properties of the obscuring material
Date: Wednesday, December 19th, 2007
Time: 12:00
Venue: Villa Bazzoni
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Abstract:
The properties (spectral energy distributions, redshifts and
luminosities) of AGN samples selected using infrared, X-ray and radio
data, separately, are compared to asses the selection biases of each
sample. By taking into account those selection effects, we estimate
the total number of AGN present in infrared-selected samples and
compare it with predictions from various models. The analysis of the
properties of the various samples shows that a mid-infrared selection
can efficiently find obscured QSOs at high redshifts. By applying
such a selection technique, we collect a remarkable sample of
extremely luminous and heavily obscured AGNs at z~2. We model their
spectral energy distributions and infrared spectra with clumpy torus
models. The models indicate that optical and mid-infrared obscuration
is caused by dust in a torus or in the host galaxy. Overall we find
that the ratio between obscured and unobscured AGN at mid-infrared
luminosities >10^12 Lsun and z~2 is 1.5-1.9:1, but only 37-40% of
these QSOs are obscured by the torus, constraining the torus half
opening angle to be about 67 degrees. This value is significantly
larger than found in far-infrared selected samples of AGN at lower
luminosity (~46 degrees), supporting the receding torus scenario.
Large far-infrared luminosities, above the predictions of the torus
model, are measured in a sub-set of these obscured QSOs, implying
extreme star formation rates (600-3000 Msun/yr) if powered by a
starburst. The implications of our results on current AGN models are
discussed and predictions for future Herschel observations of these
objects are presented.
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contact: Paolo Tozzi (OATS)