New IUE spectra for two nearby radio stations and reprocessing of archival data for four more

摘要

We obtained new IUE spectra for two nearby radio galaxies and reprocessed archival data for four more. In order to study the effects of spectral evolution in high redshift radio galaxies, we must compare these objects to the UV spectra of their most likely counterparts. We argue that their most likely low redshift counterparts are LINER's residing in giant elliptical radio galaxies. We therefore obtained and reprocessed short wavelength IUE spectra for half a dozen nearby elliptical galaxies (V less than 15 mag) with weak LINER's in their centers. Ly-alpha emission is common among local radio galaxies, at levels much weaker than those observed at high redshift. The ratio of Ly-alpha to H(alpha) in nearby objects falls well below the prediction for case B recombination, perhaps due to destruction of Ly-alpha photons by grains during resonant scattering. Many low-redshift systems show a characteristic upturn in the continuum shortward of 1500 A, which is lacking in recently studied high redshift galaxies. We extend previous comparisons and suggest that this general behavior is a direct consequence of the spectral evolution of these galaxies. The presence of this feature in nearby galaxies, and its absence in high redshift young galaxies, appears to be a general rule. We believe that this is a direct result of their spectral evolution.