Dust emission from a parsec-scale structure in the Seyfert 1 nucleus of NGC 4151
Burtscher, L.; Jaffe, W.; Raban, et al. 2009, D., The Astrophysical Journal Letters, Volume 705, Issue 1, pp. L53-L57
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0909.5191
Active Galactic Nuclei (AGN) are galaxies with an actively accreting supermassive black hole at the center. The main mechanism of the black holes consists of strong material accretion that results in the emission of broad emission lines which we can observe in the spectra (the area where the broad lines are emitted from is called the “broad line region”). This region is believed to be surrounded by a dusty torus which is a “doughnut”-shaped structure, consisting of gas and it is coplanar with the galactic plane.
The galaxies that are oriented “edge-on” relative to our line of sight (i.e. we cannot see the center directly, but we see it through this “doughnut”) are named “Seyfert type 2”, and the galaxies for which we have a direct (“top”) view are called “Seyfert type 1”. The unified model of these types of AGN states that for both type 1 and type 2 the dust distribution should be identical, and the differences observed in the detections should be caused only by the orientation relative to our line of sight. So far, though, there has not been enough supporting evidence for this theory.
The data used consists of observations made with MIDI (mid-infrared interferometric instrument) in the N energy band (radiation wavelengths between 8μm and 13μm) on the galaxy NGC 4151 (the closest Seyfert type 1). With the infrared data, Burtscher et al. 2009 were able to measure the thermal emission from the center of the galaxy.
What was found was that the temperature of the thermal emission and the diameter of the dust emission region are similar to what has been observed in the Seyfert type 2 galaxies. This is important because it is one of the first major findings that support the unification model, although numerous details need deeper analysis for a better understanding.
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