3. BROAD-LINE RADIO GALAXIES

Although about two-thirds of the sample of radio galaxies that we observed have narrow-line spectra of the type described above, the other one-third have emission-line spectra with much broader H I, He I, and He II lines. An example of one of these broad-line radio galaxies is PKS 2349-01 whose spectrum is shown in Fig. 3. Note that although the recombination lines are broad, the forbidden lines have widths similar to the line widths in narrow-line radio galaxies. Spetrophotometric results on several of these objects including 3C 120, the brightest member of the group, have been published by Koski, Phillips and myself [16 - 18]. Within this group the widths of the H I lines cover a wide range, with full width at zero intensity ranging from 1.4 x 10⁴ km/s in 3C 227 and 3C 445 to 2.5 x 10⁴ km/s in 3C 382. The full widths at half maximum range from 2.0 x 10³ km/s up to 1.8 x 10⁴ km/s, but these are less meaningful, because in many cases the H I line profiles are composite, containing both a broad component and a narrow component, the latter having the same width and redshift as the forbidden lines. This can be seen very clearly for instance in the H emission line of PKS 2349-01. In some of these broad-line radio galaxies the strength of the broad components falls off much more rapidly with increasing n than the narrow component, so that H is often dominated by the broad component, at H the broad component is often easily seen while at H it is in some cases barely detectable. Our measurements show the profiles are often asymmetric, contain a good deal of real fine structure, and certainly differ in width from one broad-line radio galaxy to another. The narrow-line spectra of the broad-line radio galaxies are similar in measured relative intensities to the spectra of narrow-line radio galaxies, and it thus appears that all of these objects have similar physical conditions in the narrow-line emitting region, but the broad-line galaxies have an additional region unique to them in which the range of velocities is much higher.

Figure 3. Measured spectrum of broad-line radio galaxy PKS 2349-01 in relative energy per unit wavelength in interval versus wavelength. (The dip in the continuum near 5450 is not real.)

In the course of our spectral survey of radio galaxies with emission lines in their spectra it soon became evident that there is a good correlation between the widths of the recombination lines and the form of the galaxy. It was noted [10] that most of the broad-line radio galaxies tend to be N galaxies, characterized by having brilliant starlike nuclei containing most of the luminosity of the systems, together with faint nebulous envelopes of small visible extent. On the other hand most of the narrow-line radio galaxies tend to be E, D or DE galaxies. To test this conclusion we added to the program more radio galaxies known to have broad H I emission lines or known to be N galaxies. The results, published by Grandi and myself [19], show that there is a very high correlation between the broad-line spectral character and the N form classification. Of fifteen definite broad-line radio galaxies, ten are N galaxies, two may or may not be N galaxies (both classifications exist for these two objects in the published literature), and only three are definitely not N galaxies. Of three additional objects for which we could not get spectra at H because of their large redshifts, but which appear to be narrow-line radio galaxies at H, two are N galaxies while one is not an N galaxy. It would be most interesting to observe these three objects, 3C 99, 3C 171, and 4C 39.72, further in infrared than we can go, to see if they in fact show the broad component at H, as for instance 3C 234 and 3C 332 do. It would also be interesting to obtain spectra of a sample of N galaxies that are not radio galaxies, to see what fraction of them have emission- line spectra, and of these what fraction have the broad-line feature, but there apparently are no published lists of N galaxies that are not radio sources. One additional N radio galaxy known to be a broad-line radio galaxy is Pic A, observed by Danziger, Fosbury and Penston [20] with the Wampler-Robinson scanner formerly used on the 120inch telescope at Lick Observatory but later loaned to the Anglo-Australian Observatory.