Daily Image
04-03-2010
Today's colloquium: Resolving the dusty cores of nearby AGN with mid-infrared interferometry (Konrad Tristram, MPIfR)
| Submitter: | Stefanie Muehle |
| Description: | A geometrically thick component of dust and gas is a key component of active galactic nuclei (AGN). This so-called "dusty torus" is thought to provide the material for feeding the supermassive black hole as well as to cause the viewing-angle dependent obscuration towards the central engine. The energy absorbed by the torus is mainly reemitted at infrared wavelengths. A direct study of the torus has been difficult because it is essentially unresolved at these wavelengths even by the largest single dish telescopes. A great breakthough in the study of the nuclear material has been obtained by infrared interferometry, mostly in the mid-infrared with the MIDI instrument at the Very Large Telecope Interferometer (VLTI). With MIDI it has been possible to directly confirm the existence of parsec-scaled warm dust structures in the nuclei of several nearby Seyfert galaxies and to show that the size of the dust structures roughly scale with the square root of the AGN luminosity. Between individual nuclei, however, there are significant differences in the torus orientation, in its temperature profile and in the behaviour of the silicate feature. Thus it seems that there is no such thing as a standard dusty torus in Seyfert galaxies but rather that there are significant differences between the dust distributions in individual objects. This and the upcoming results from new observations are a great step towards understanding the role of the nuclear gas and dust distribution for the appearance and the functioning of AGN. The figure above shows the parsec-scaled dust distributions in the nuclei of NGC 1068 and the Circinus galaxy in the context of their immediate environment, such as ionisation cones and jets. |
| Copyright: | K. Tristram |
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