Morphological peculiarities of high-redshift radio galaxies: The role of relativistic electrons

High-redshift radio galaxies are very powerful, extended, double radio sources; the radio emission from these systems indicates that the relativistic electrons have a significant amount of energy. The peculiar morphologies of high-redshift radio galaxies appear to be related to the relativistic electron populations since the optical continuum and emission-line regions are elongated and aligned with the radio axes. A close connection with the relativistic electron population is also indicated by the relationships between the radio power and the emission-line luminosity and between the radio spectral index and the optical to near-infrared colors of these systems. Five models (two new and three previously proposed) to explain the peculiar optical and emission-line morphologies of high-redshift radio galaxies are discussed in detail here: the inverse Compton scattering model, bremsstrahlung and the line emission from clumped hot gas, jet-induced star formation, Thomson scattering of anisotropic light emitted by the AGNs, and optical synchrotron radiation are considered; the models are summarized in § 10. Relativistic electrons are likely to play an important role in the optical and emission-line properties of high-redshift radio galaxies via interactions between the relativistic electrons and the ambient gas, and via inverse Compton scattering of microwave background photons with the relativistic electrons. In addition, the environments of the radio galaxies and constraints on the orientation unified model for radio galaxies and radio-loud quasars are discussed.