|
Description
We present results from a program of optical imaging of 265 radio galaxies in rich clusters. Using isophotal surface photometry, we investigate the optical properties such as the morphology, surface-brightness profiles, surface-brightness/size relationships, ellipticities, and the frequency of nonelliptical isophotes. The results are compared to a "normal" nonradio-selected sample of elliptical galaxies from the same clusters. The goal is to determine if the parent population of FR I radio galaxies can be distinguished optically from radio-quiet galaxies. The results of the analysis are that cluster ellipticals are a very homogeneous class of objects. The optical properties are consistent with a one-parameter family, where the optical luminosity is the fundamental parameter. In all tests considered, radio-loud FR I galaxies cannot be distinguished optically from radio-quiet galaxies selected from the same environment. The local density of nearby companions (<20kpc) and the frequency of morphological peculiarities or tidal interactions are not statistically different between the radio-loud and quiet samples. There is some suggestion from comparison to published samples of non-cluster radio galaxies, that the cluster environment is not condusive to long-lived tidal interactions, and that such events may be more important to galaxy evolution in poor groups and lower density environments. Such events appear to have little influence on the formation of FR I radio galaxies in rich clusters. The results are consistent with the idea that all elliptical galaxies may at some time (or many times) contain powerful (FR I) radio sources.
|
