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The miniatures on this page link to full-size radio images of quasars selected from the Revised 3C Catalogue of Radio Sources. The images were made with the NRAO Very Large Array (VLA) at 4.9 GHz (6cm) in its highest-resolution mode ("A" configuration). They are among the most detailed views ever obtained of the extended radio emission from radio-loud quasars.
Quasars are the brilliant, unresolved nuclei of active galaxies. Not all quasars are strong radio sources, but some are so powerful that their radio emission can be detected across the entire known Universe.
These images show the rich internal structures of radio "lobes" built up over millions of years by outflows from the nuclei of such "radio-loud" quasars. The outflows excavate enormous cavities in the intergalactic medium around the quasar, and refill these cavities with relativistic plasma and magnetic fields. The radiation from electrons spiralling in these magnetic fields makes the lobes visible to radio telescopes. The slender radio "jets" seen in these images reveal the paths of the outflows. The jets link pointlike radio sources in the active nuclei to "hot spots", bright emission complexes where the lobe plasma has recently been compressed by the passage of the outflow. We believe that a movie of a lobe growing over millions of years would show the end of the jet "thrashing" as the lobe grows, forming transient "hot spots" at many different places at different times. Thus each of these images is probably a "snapshot" of a dynamic, changing situation.
Although lobes form on both sides of each quasar, implying that there are two oppositely-directed flows in each case, the radio emission received from one jet is always much brighter than that from the other. We think this asymmetry is a consequence of flow speeds approaching that of light. A flow moving towards us at almost the speed of light catches up with its own radiation, which thereby appears boosted in intensity -- the brighter jet. In contrast, the radiation from a flow moving away from us is correspondingly dimmed, making a fainter "counterjet".
These images were obtained during a search for such brightness asymmetries, exploring how far from the quasar such high velocities persist. They provided evidence for outflows at a significant fraction of the speed of light many tens, even hundreds, of kiloparsecs from the quasar nucleus. For technical details, see Deep VLA Imaging of Twelve Extended 3CR Quasars, by Alan H. Bridle, David H. Hough, Colin J. Lonsdale, Jack O. Burns and Robert A. Laing, The Astronomical Journal, 108, 766-820 (1994).
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Last updated: 13 November 1996, 16:19 EST