RADIO BRIDGE STRUCTURE AND ITS APPLICATION TO ESTIMATE THE MACH NUMBER AND AMBIENT GAS TEMPERATURE OF POWERFUL SOURCES

摘要

The radio bridge shape of very powerful extended (FR II) radio sources has been studied in detail; the sample used here includes 12 radio galaxies and six radio-loud quasars with redshifts between 0 and 1.8. Specifically, the width and radio surface brightness of the radio bridge are measured as a function of distance from the radio hot spot on each side of each source. The width as a function of distance from the hot spot agrees very well with theoretical predictions based on the standard model of bridge growth, in which the bridge expands laterally because of a blast wave driven by the large pressure difference between the relativistic plasma in the radio hot spot and surrounding radio lobe and the adjacent ambient gas. The simple assumptions that go into the theoretical prediction are that the lobe radio power and width (measured in the vicinity of the radio hot spot) are roughly constant over the lifetime of a given source, and that the rate at which the bridge lengthens, referred to as the lobe propagation velocity, is roughly constant over the lifetime of a source. These three assumptions appear to be consistent with other independent studies of very powerful extended radio sources of the type studied here, within the present (rather large) observational uncertainties.