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Cyg A = 3C 405 is one of the brightest radio sources in the sky, a cD galaxy known from the work of Baade and Minkowski [11] to have very strong emission lines. Miller and I [12] measured the relative intensities of 24 emission lines in its spectrum, the strongest being [O III] lambda5007 and [N II] lambda6583. A very wide range of ionization is observed from [O I], (N, I], and [S II] all the way to [Ne V], [Fe VII] and [Fe X]. The latter is represented by lambda6374, which was reported to be present by Baade and Minkowski because the wavelength of [O I] lambda6364 which they measured was too large. It can definitely be seen to be present in our scans, both from the asymmetric form of the blended profile and from its relative intensity with respect to [O I] lambda6300. [Fe XIV] lambda5303 could not be detected in our spectra, but the upper limit we could place on it is only a trifle smaller than the measured [Fe X] lambda6374 strength. In a general way, the emission lines detected in Cyg A, particularly those of intermediate ionization, are the same lines that are strong in planetary nebulae and H II regions, implying that the abundances of the elements, temperatures, and densities are not vastly different in these classes of objects, although this subject is treated in more detail in my other paper in this symposium.

The emission lines in Cyg A all have similar profiles, with full widths at half maximum of approximately 500km/s. The H I Balmer lines have a very steep gradient, and since for a very wide range of electron temperatures and densities we expect the emitted decrement to fall within the relatively narrow range predicted by the recombination theory, the only plausible interpretation is that the observed line strengths have been strongly modified by interstellar extinction. The amount of extinction derived from the H I line corresponds to about EB-V = 0.7 magnitudes, assuming the standard Whitford reddening curve. All the measured emission-line strengths were corrected with this reddening to derive the relative line intensities as emitted in Cyg A.

The continuous spectrum of Cyg A shows no detectable absorption lines whatsoever at our resolution. The observed continuous spectrum approximately fits a power-law

Fnu = C nu-n

with n = 2.7, or if the correction for interstellar extinction derived from the H I emission lines is also applied to the continuum, n = 1.6.

Figure 1

Figure 1. Upper - measured spectrum of narrow-line radio galaxy 3C 33; lower - measured spectrum of Seyfert 2 galaxy Mrk 348. Both spectra plotted in relative energy units per unit frequency interval versus wavelength.

Spectrophotometric measurements of several other "narrow-line radio galaxies" similar to Cyg A have been carried out and reported by Costero and myself [13] and by Koski [14, 15]. All these radio galaxies have emission lines with widths similar to the widths in Cyg A, ranging between about 400 km/s and 800km/s in various members of the group. Most of them have emission-line spectra similar to that of Cyg A, though weaker by various amounts with respect to their continuous spectra. A few of the narrow-line radio galaxies have emission-line spectra indicating a generally lower level of ionization, with [O III] lambda5007 weaker with respect to Hbeta, and [O II] lambda3727 stronger. An example is PKS 2322-12, whose spectrum is shown in Fig. 2. However this object, and other narrow-line radio galaxies we have observed with similar low average levels of ionization, could not be mistaken for typical H II regions or low-ionization planetary nebulae, because [O I] lambdalambda6300, 6364 and [S II] lambdalambda6717, 6731 are much stronger in the radio galaxies than in any H II region or planetary nebula.

Figure 2

Figure 2. Measured spectrum of narrow-line radio galaxy PKS 2322-12 in relative energy units per unit frequency intervarl versus wavelength.

All the narrow-line radio galaxies we have observed except Cyg A have detectable absorption lines in their spectra, the lines most easily seen being Mg I lambda5190 and Ca II H and K. In many cases a detailed comparison shows that many more lines of an underlying galaxy can be seen, but in general the equivalent widths of the absorption lines in the radio-galaxy spectra are smaller than in typical galaxies. Evidently the optical spectra of radio galaxies we have observed can be described as combining an emission-line spectrum, a featureless continuum, and an absorption-line galaxy spectrum. Quantitative measurements by Koski [14] indicate that the featureless ("power-law") continuum makes up from 0.1 to 0.7 of the total continuous spectrum at Hbeta in the objects he observed. In several of the narrow-line radio galaxy spectra, H I absorption lines can be seen in the near ultraviolet, indicating the presence of more early type stars than in typical galaxies. These features do not occur in all narrow-line radio galaxies; in some the absorption-line spectrum is a very good match indeed to the absorption-line spectrum of a normal elliptical galaxy.

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