Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aj....118.1461t&link_type=abstract
The Astronomical Journal, Volume 118, Issue 4, pp. 1461-1467.
Astronomy and Astrophysics
Astronomy
12
Galaxies: Active, Galaxies: Individual (Cygnus A), Infrared Radiation
Scientific paper
We present optical and near-infrared spectroscopy of the luminous radio galaxy Cygnus A (3C 405). Optical (~6700-9300 Å) observations were obtained of the central region, including the region where most emission lines are strongest, about 1.5" northwest of the nucleus. However, high-ionization lines ([Ar XI] and [Fe XI]), as well as an unidentified feature at ~7608 Å, are stronger in the continuum-dominated southeast component. We detect the near-infrared Ca triplet in absorption, and we use it to obtain a new determination of the redshift and velocity dispersion of the stellar component of Cygnus A. The infrared (~1.9-2.5 μm) spectrum of the nucleus shows emission from [Si VI], [S XI], and possibly [Si XI]. A number of molecular hydrogen transitions were also detected; their ratios favor X-ray heating from the nuclear source over other possible origins (e.g., shocks) as the most likely excitation mechanism. We see no evidence for broad-line wings on the Paα line profile, confirming that the broad-line region in Cygnus A remains heavily obscured at 2 μm.
Ridgway Susan E.
Stockton Alan
Thornton Robert J. Jr.
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