2009/02/06 by R. E. Mason, Rachel Mason, N. A. Levenson +10
Physics and Astronomy · #Active galactic nucleus #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Geometry #Line (geometry) #Physics #Silicate #Spectral energy distribution #Spectral line #Stellar, planetary, and galactic studies #Torus #astro-ph.GA
paper · pdf · doi:10.1088/0004-637x/693/2/l136
ApJL, accepted
arxiv created 2009/02/06 · openalex publication_date 2009/02/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
The unified model of active galactic nuclei (AGNs) predicts silicate emission features at 10 and 18 μm in type 1 AGNs, and such features have now been observed in objects ranging from distant quasi-stellar objects to nearby LINERs. More surprising, however, is the detection of silicate emission in a few type 2 AGNs. By combining Gemini and Spitzer mid-infrared imaging and spectroscopy of NGC 2110, the closest known Seyfert 2 galaxy with silicate emission features, we can constrain the location of the silicate-emitting region to within 32 pc of the nucleus. This is the strongest constraint yet on the size of the silicate-emitting region in a Seyfert galaxy of any type. While this result is consistent with a narrow-line region origin for the emission, comparison with clumpy torus models demonstrates that emission from an edge-on torus can also explain the silicate emission features and 2–20 μm spectral energy distribution of this object. In many of the best-fitting models the torus has only a small number of clouds along the line of sight, and does not extend far above the equatorial plane. Extended silicate-emitting regions may well be present in AGNs, but this work establishes that emission from the torus itself is also a viable option for the origin of silicate emission features in active galaxies of both type 1 and type 2.