Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.245..408s&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. Vol. 245, No. 3, p. 408 - 426
Astronomy and Astrophysics
Astronomy
36
Radio Galaxies: Radio Structure, Radio Galaxies: Vla Observations, Quasars: Radio Structure, Quasars: Vla Observations, Quasars: Relativistic Beaming
Scientific paper
To investigate the nature of extragalactic radio sources with extended emission on only one side of the active nucleus, the authors have observed a sample of suspected candidates with both the VLA and MERLIN. In this paper, they present observations of 13 sources which were either suspected of being "one-sided" or were known to have lobes of very different surface brightnesses. Many of the candidates were found to have emission on both sides of the nucleus. Using their observations as well as those available in the literature, the authors have compiled a sample of 4C quasars having one-sided radio structure. They have then compared some of their properties with a sample of 4C quasars which are two-sided, in order to determine whether their apparently one-sided structure is due to relativistic beaming in sources inclined at small angles to the line-of-sight. The authors find that the median values of fc, the fraction of emission from the core used as a statistical measure of source orientation, and l, their projected linear sizes, are consistent with the hypothesis that the one-sided quasars are seen at smaller angles to the line-of-sight than the two-sided ones. The authors also suggest that the φ-fc relation for quasars, where φ is the angle between the core polarization vector and the overall radio axis, is consistent with this model, and discuss how the lobe depolarization properties may be useful for further investigations of this interpretation. The velocities required to explain the apparently one-sided quasars in the relativistic beaming framework are in the range of ˜0.2-0.8c. The scarcity of high-luminosity, Fanaroff-Riley class II radio galaxies with one-sided structure is consistent with the suggestion that they are at larger angles to the line-of-sight than quasars. In this case, the core-dominated radio galaxies are possibly the low-luminosity, Fanaroff-Riley class I radio galaxies seen at small angles to the line-of-sight, manifesting themselves as BL Lac objects in the more extreme cases.
Cornwell Tim J.
Junor William
Muxlow Thomas W. B.
Saikia D. J.
Shastri Prajval
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