SEMINAR ANNOUNCEMENT - OATS-DAUT Seminar - Wednesday, 19th December at 12:00 (Villa Bazzoni)

[Gabriella Schiulaz]

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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 (via Bazzoni, 2)

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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) 



The first 2008 seminar is scheduled on Wednesday 9th January as follows:
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               OATS-DAUT SEMINAR 
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Speaker: Marco Fulle (INAF/OATS) 
Title: Iron tails 

Date: Wednesday, January 9th, 2008 
Time: 12:00 
Venue: Villa Bazzoni 
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Abstract: 
In January 2007, at the heliocentric distance r < 0.3 Astronomical Units, comet McNaught 2006P1 became the brightest comet since C/Ikeya-Seki 1965S1 and was continuously monitored by space-based solar observatories. An arch-like tail observed by the Heliospheric Imager aboard the STEREO spacecraft is the first ever detected tail composed of neutral Fe atoms, providing the first estimate of the Fe lifetime, which results in 4.1 ± 0.4 104 s at r = 0.25 AU, in agreement with theoretical predictions of photo-ionization lifetime. The expected dust temperature is inconsistent with iron sublimation, suggesting that Fe atoms are coming from troilite evaporation, in agreement with Stardust samples which contain most iron in such sulfides. 
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contact: Marco Fulle (OATS) 


For additional information on OAT seminars see:
http://adlibitum.oats.inaf.it/seminari/

Gabriella Schiulaz
segreteria OAT
Phone: 040-3199241
schiulaz at oats.inaf.it
segreteria at oats.inaf.it