Long-Slit Spectroscopy of 3C 31, 3C 75, 3C 465, NGC 1265, and Cygnus A

We present results of long slit optical spectroscopy of five radio galaxies (3C 31, 3C 75, 3C 83.1B [NGC 1265], 3C 405 [Cygnus A], and 3C 465). We oriented the slit at various different positions with respect to the radio sources in order to look for emission from plasma in the radio jets and lobes, hypothetical dense clouds at bends in the jets, and emission from the general surrounding medium. In most cases no extra-nuclear emission was detected. This allows us to set temperature and density limits for gas in the various volumes studied assuming equilibrium with the pressures implied by Einstein X-ray observations. These limits were obtained mainly from the Hα, Fe X (λ6374), and Fe XIV (λ5303) lines. These results rule out or set constraints on a number of models for the radio sources. We rule out models involving cool deflecting clouds for bending 3C 465 and 3C 75, except with a very unlikely combination of parameters. We also find that our data is inconsistent with heavy jet models for 3C 31. The temperature in the interstellar medium of NGC 1265 is found to exceed 3 x 10^6^ K and that the interstellar magnetic field must exceed 0.08 μG. We also find that the large rotation measures seen in Cygnus A are probably produced in a foreground screen of hot gas rather than in a cool boundary layer between the radio source and the intercluster medium. In 3C 31, in addition to obtaining limits far from the nucleus, we detected extended emission apparently associated with a rotating disk of gas associated with a dust lane originally reported by Butcher, van Breugel, and Miley.