Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21541119m&link_type=abstract
American Astronomical Society, AAS Meeting #215, #411.19; Bulletin of the American Astronomical Society, Vol. 42, p.243
Astronomy and Astrophysics
Astronomy
Scientific paper
According to the unified model of active galactic nuclei (AGN), the central engine is obscured by optically thick clouds in a toroidal geometry. A significant fraction of the energy from the central engine is absorbed by this torus, and re-emitted at mid-infrared (MIR) wavelengths. Since the composition and geometry of the torus remain uncertain, MIR observations provides valuable insight into unification theories. We present the results of our MIR spectroscopic observations of the radio loud AGN Cygnus A using COMICS on the Subaru 8.2m telescope. While MIR space-based observations afford greatly superior sensitivity, ground-based observations on 8m-class telescopes, achieve improved spatial resolution approaching 0.3''. Of particular interest in the 10 micron band are the 9.7 micron silicate feature and the 10.5 micron [S IV] line. Our diffraction limited observations measure the silicate feature's optical depth of 1.28±0.42, compared with the 0.49±0.15 measured from Spitzer data. Splitting the nuclear region into three 0.66'' apertures, the central aperture gives an optical depth of 0.99±0.22 while the east and west offsets show differences in the spectral shape and differences in optical depths, 1.76±3.18 and 2.04±1.19 respectively. We can not conclude where the maximum optical depth occurs because of the large errors present in the offset data. The [S IV] line has an equivalent width of 0.25 microns, a flux of 2.66 mJy, and a FWHM of 0.06 microns. This data is compared to clumpy torus models to help constrain the structure and composition. We also compare and contrast the mid-IR features with features seen in the radio, optical, and x-ray bands to gain a more complete picture of structures present in Cyg A.
Aretxaga Itziar
Imanishi Masatoshi
Levenson Nancy
Mason Rachel
Merlo Matthew J.
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