Journal Article

‘Normal’ Fanaroff–Riley type II radio galaxies as a probe of the nature of X-shaped radio sources

Dharam V. Lal, Martin J. Hardcastle and Ralph P. Kraft

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 390, issue 3, pages 1105-1116
Published in print November 2008 | ISSN: 0035-8711
Published online October 2008 | e-ISSN: 1365-2966 | DOI:
‘Normal’ Fanaroff–Riley type II radio galaxies as a probe of the nature of X-shaped radio sources

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We present a multiwavelength radio study of a sample of nearby Fanaroff–Riley type II (FR II) radio galaxies, matched with the sample of known X-shaped radio sources in size, morphological properties and redshift, using new Giant Metrewave Radio Telescope (GMRT) data and archival data from the Very Large Array. Our principal aim in this paper is to provide a control sample for earlier studies of samples of ‘X-shaped’ radio sources, which have similar luminosities and small-scale radio structures to our targets but exhibit large-scale extensions to their lobes that more typical FR II sources lack; earlier spectral work with the GMRT has suggested that these ‘wings’ sometimes have flat spectral indices at low frequencies, in contrast to the expectations from models in which the wings are formed hydrodynamically or by jet reorientation. In our new observations, we find that almost all of our target FR II radio galaxies show standard spectral steepening as a function of distance from the hotspot at the low frequencies (610 and 240 MHz) provided by the GMRT data, even when transverse extensions to the lobes are present. However, one source, 3C 321, has a low-surface-brightness extension to one lobe that shows a flatter spectral index than the high-surface-brightness hotspots/lobes, as found in X-shaped sources.

Keywords: galaxies: active; galaxies: formation; radio continuum: galaxies

Journal Article.  7949 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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