1. INTRODUCTION

Seyfert galaxies have been recognized as highly interesting, though rare, galaxies with active nuclei since the isolation of this class of objects by Seyfert [1] and their discussion in physical terms by Woltjer [2]. Basically they may be described as galaxies with unusually bright nuclei having strong, broad emission lines extending to high stages of ionization in their spectra. An additional criterion often stated is that the nuclei have relatively strong nonstellar blue or ultraviolet continuous spectra. With the first identifications of radio galaxies by Baade and Minkowski [3] it became clear that a large number of these objects have emission-line spectra similar in many ways to the spectra of Seyfert galaxies. For instance, in a survey by Schmidt [4] about twelve years ago, among 35 radio galaxies for which he obtained optical spectra all but three were found to have [O II] 3727 in their spectrum, and about 23 of these objects, or two-thirds of the sample, also show [O II] 4959, 5007 in emission. About one-half the objects in this sample also have additional detectable emission lines and spectra which may be described qualitatively as at least one-third as strong as the emission-line spectrum of Cygnus A. In a more recent survey by Smith, Spinrad, and Smith [5], optical identifications are listed for 139 radio galaxies in the revised 3C catalog of radio sources. Brief descriptive information is given in this reference on the spectra of 97 of these radio galaxies, of which 49 have strong emission-line spectra, 18 have intermediate-strength emission lines, 12 have weak emission lines, and 18 have pure absorption-line spectra without detectable emission features. The fraction of these objects with emission-line spectra is clearly much higher than in normal galaxies, and it is evident that although the presence of emission lines is neither a necessary nor sufficient condition that a galaxy be an observable radio source, a very large proportion of radio galaxies do contain ionized gas in their nuclei.

Many descriptions have been published of the spectra of radio galaxies, largely concerned with identifications, measurements of redshifts, and lists of lines observed. However as much remains unknown about the physics of radio galaxies it seemed worthwhile to use the Lick Observatory image tube-image dissector spectrograph developed by Wampler, Robinson, and Miller [6 - 8] for a spectrophotometric survey of radio galaxies with emission lines in their spectra. Because of the sky-subtraction feature of this instrument, it is possible to detect and measure fairly accurately even weak emission lines, and the program was designed to provide information on the emission-line strength and profiles, as well as the absorption-line equivalent widths and the continuous spectra of a large number of radio galaxies. It is this material that I will describe in the present paper, although it must be realized that I am omitting many references to earlier work, chiefly photographic and image-tube spectra by Burbidge, Lynds, Sandage, Schmidt, Spinrad, Strittmatter and others, which led us to obtain spectra of objects described in this paper.

First a brief word on the observational techniques, which are described in more detail in the individual references cited below, and in two earlier summaries of the results obtained [9, 10]. All the spectrograms are taken with a 2".7 x 4" slit centered on the nucleus, and generally speaking a large fraction but (particularly in poor seeing) not all of the light of the nucleus is measured. The spectra have a resolution (measured full-width at half-maximum of a much narrower comparison line) of about 10 Å, and cover approximately 2400 Å, so we generally take a blue spectrum and a red spectrum of each object, covering together the range 3400-7500, with a considerable overlap in the middle. The spectra are calibrated into energy units by spectra of standard stars taken the same night, and the effects of atmospheric extinction are removed using standard extinction coefficients supplemented by measurement of the H₂0 and strong O₂ bands in the standard stars the same night. These bands often strongly affect the H region for galaxies with redshifts in the range we can observe.