Séminaire/Seminar Galaxies |
| « The weather around Active Galactic Nuclei - From X-rays to IR » |
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Robert Nikutta |
| The evidence for clumpiness of the gaseous, dusty medium surrounding the central AGN engine is mounting. There is growing consensus that the distribution of material is not smooth, at least not all of it. I will introduce the CLUMPY radiative transfer models for AGN tori (Nenkova et al. 2002,2008) and show how we use them to understand the observational evidence, both in X-rays and in the IR domain. Analyzing 16 years of X-ray observations in AGN with RXTE, we recently found 12 secure eclipse events and several candidates. In a recent paper (Markowitz, Krumpe, Nikutta, 2014) we show that these events are discrete gas+dust clouds crossing our line of sight. Due to RXTE"s long mission duration, it was sensitive to eclipses caused by clouds much further away from their AGN than previously reported events. Our clouds are located both in the BLR and also well into the dusty part of the cloud distribution, the ""torus"". Because the number of events found by RXTE is quite large, we were able to perform a statistical analysis and derive ""instantaneous"" probabilities to observe an AGN in an obscured state. In a follow-up (Nikutta, Krumpe, Markowitz, in prep.) we constrain the properties of the clouds further, and test the predictions of most recent AGN torus models. Using Bayesian inference together with the CLUMPY models, we can derive most of the parameters that govern the distribution of clouds in the BLR and in the torus. This provides a natural connection between the AGN X-ray light and the Infrared emission, a signature of the dusty AGN torus. I will show how using the large WISE catalog we can reliably identify type-1 and type-2 AGN through their IR properties, putting AGN unification to the test. |
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jeudi 4 septembre 2014 - 11:30 Salle 281 Institut d'Astrophysique de Paris |
| Page web du séminaire / Seminar's webpage |