Stellar dynamics of powerful radio galaxies

We present new data and results on the stellar dynamics of powerful radio galaxies (P_178MHz_ > 10^24^ W Hz^-1^). These data were obtained with the KPNO 4 m using the R. C. spectrograph and a TI CCD. Rotation velocities and stellar velocity dispersions were determined using a Fourier quotient technique. These new data on 20 galaxies are combined with similar data in the literature to generate a total sample of 47 powerful radio galaxies. We compare the stellar kinematics of these strong radio source galaxies to those of normal, bright ellipticals to search for evidence of large galactic rotation velocities and/or unusual velocity dispersions. In addition, we compare the stellar kinematics of several different subgroups of powerful radio galaxies (normal/peculiar optical morphology, and presence/absence of optical emission lines) with one another. In agreement with previous investigations, we find little difference between the stellar dynamical properties of the powerful radio galaxies (when averaged over all subgroups) and those of normal elliptical galaxies. More detailed examination of the various subgroups in the sample reveals important distinctions, however. Our primary conclusion is that powerful radio galaxies with peculiar optical morphologies appear to be dynamically peculiar as well: their stellar velocity dispersions are lower than those of both elliptical galaxies and powerful radio galaxies with normal optical morphologies, and they show evidence for more rotational support. Furthermore, when we divide the sample into two subgroups, those with strong optical emission-lines and those without, similar distinctions are found. The strong emission-line galaxies tend to have lower velocity dispersions and to exhibit a larger degree of rotational support. Despite the many unusual properties powerful radio galaxies possess, they do, for the most part, appear to lie within the "fundamental plane" of elliptical galaxies defined by the parameters r_e_ <μ_e_), σ. We find that the stellar velocity dispersions and emission-line full widths at half- maxima are well correlated. This suggests that the kinematics of both the stars and the gas are dominated by the same gravitational potential. Mass- to-light ratios for the normal morphology radio galaxies are similar to those of bright elliptical galaxies. However, the mass-to-light ratios of the morphologically peculiar galaxies are a factor of ~ 2 smaller than their normal morphology counterparts. As with previous studies, we find no correlation between the stellar kinematics and the radio power of the galaxies in this sample. These results greatly strengthen the case for some fraction of powerful radio galaxies being the product of a merger of two galaxies, at least one of which was a disk system. Those powerful radio galaxies which are morphologically peculiar exhibit greater degrees of rotation, have increased optical emission-line strengths, show bluer than normal continuum colors, and exist in relative isolation from neighboring galaxies are most probably the result of such a merger.