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

We present amultiwavelength radio study of a sample of nearby Fanaroff-Riley class II (FRII) 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 (VLA). 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 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 FRII radio galaxies show standard spectral steepening as a function of distance from the hotspot at the low frequencies (610 MHz and 240 MHz) provided by the GMRT data, even when transverse extensions to the lobes are present. However, one source, 3C321, 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.