Optical and near-infrared spectroscopy of Cygnus A

We present optical and near-infrared spectroscopy of the luminous radio gal axy Cygnus A (3C 405). Optical (similar to 6700-9300 Angstrom) observations were obtained of the central region, including the region where most emiss ion lines are strongest, about 1." 5 northwest of the nucleus. However, hig h-ionization lines ([Ar XI] and [Fe XI]), as well as an unidentified featur e at similar to 7608 Angstrom, are stronger in the continuum-dominated sout heast component. We detect the near-infrared Ca triplet in absorption, and we use it to obtain a new determination of the redshift and velocity disper sion of the stellar component of Cygnus A. The infrared (similar to 1.9-2.5 mu m) spectrum of the nucleus shows emission from [Si VI], [S XI], and pos sibly [Si XI]. A number of molecular hydrogen transitions were also detecte d; their ratios favor X-ray heating from the nuclear source over other poss ible origins (e.g., shocks) as the most likely excitation mechanism. We see no evidence for broad-line wings on the Paa line profile, confirming that the broad-line region in Cygnus A remains heavily obscured at 2 mu m.