Guenther Hasinger
Max-Planck-Inst. Physik (Munich, Allemagne)
Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris
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| « The evolution of AGN and the X-ray background » |
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Guenther Hasinger |
| Deep X--ray surveys have shown that the cosmic X--ray background (XRB) is largely due to the accretion onto supermassive black holes, integrated over the cosmic time. These surveys have resolved more than 80% of the 0.1-10 keV X--ray background into discrete sources. Optical spectroscopic identifications show that the sources producing the bulk of the X--ray background are a mixture of obscured (type-1) and unobscured (type-2) AGNs, as predicted by the XRB population synthesis models. A class of highly luminous type-2 AGN, so called QSO-2s, has been detected in the deepest Chandra and XMM-Newton surveys. The ratio of obscured to unobscured objects, however, is a strong function of luminosity, with much fewer high-luminosity absorbed objects, calling the strong AGN unified model into question. The new Chandra AGN redshift distribution peaks at much lower redshifts (z around 0.7) than that based on ROSAT data, and the new X-ray luminosity function indicates that the space density of Seyfert galaxies peaks at significantly lower redshifts than that of QSOs. It is shown, that the low redshift peak applies both to absorbed and unabsorbed AGN and is also seen in the 0.5-2 keV band alone. Consequences for the formation and growth of supermassive black holes in galactic centers are discussed. |
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lundi 27 octobre 2003 - 11:00 Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris |
| Page web du séminaire / Seminar's webpage |