Spectra of compact and extended components of powerful extragalactic radio sources

High-resolution observations of six powerful extragalactic radio sources made between 327 MHz and 5 GHz have enabled separation of the compact and extended features and the determination of spectra of these features over a large frequency range. In four sources the outer components are connected by continuous bridges, three of which have spectra significantly steeper than those of the outer components. For at least two sources, brightness of the extended features is found to decrease rather sharply with distance from the compact 'heads' located near their outermost edges. In these sources, prominent long tails are not seen even at 327 MHz, contrary to expectation for models in which energetic particles escape continually from the heads. The observed similarity between spectra of the short tails and compact heads and between the extents of the short tails at widely separated frequencies seems to indicate that, apart from adiabatic and radiative losses, particles within the short tails may also be subject to some energy-gain processes. Compact heads in three sources contain scintillating components which are several hundred times smaller than the overall extents of these sources. Internal pressure within these components seems to be too high to be balanced by ram pressure of the intergalactic medium, suggesting that they represent the occurrence of some transient activity, resulting from instabilities or a recent input of energy. (author)