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4. RELATIVE ORIENTATIONS OF RADIO AND HOST OPTICAL AXES AND THE FR CLASSIFICATION

Saripalli & Subrahmanyan (2009) studied the relative orientations of radio and host optical axes of the 3CRR FR-II sample and found that there was no preferred relation; the radio axes are distributed over a wide range of angles from 0 to 90 with respect to the major axes. Several previous studies also reported the same lack of relation between the radio and host optical axes for FR-IIs (Palimaka et al. 1979, Guthrie 1980, Sansom et al. 1987). Curiously, it was only more recently that this study was performed for FR-I type radio galaxies. Browne & Battye (2011) used a large sample of FIRST radio sources identified with SDSS galaxies for which they derived the radio and host optical axes orientations and they reported a strong tendency for radio axes in their (largely FR-I radio galaxies) to be oriented along the host minor axis. Interestingly, this commonality of radio and host minor axes position angles is not shown by the stronger of their FR-I sources.

Once again these clear differences between the relative orientations of radio and host optical axes need to be brought within any wider framework seeking to understand the two FR types.