Depolarization and other asymmetries in double radio sources
Peter C. Tribble
Canadian Institute for Theoretical Astrophysics, 60 St. George
Street, Toronto M5S 1A1, Canada
(Present address: Institute of Astronomy, Madingley Road, Cambridge
Accepted 1991 December 12. Received 1991 December 2; in original form
1991 August 20.
The presence of a one-sided jet in double radio sources is often
interpreted as an orientation effect due to relativistic beaming. The
counterjet side is more depolarized, consistent with a larger path
length through a depolarizing medium. I consider this and other
asymmetries in detail. The polarization curves of a small sample are
shown to be consistent with the expected behaviour of a source behind a
partially resolved foreground screen. I model the depolarization
asymmetry and show how the orientation angles of the sources can be
found. There is a deficit of sources in the plane of the sky for the
Garrington et al. sample, although this may be a selection effect.
Depolarization is only correlated with arm-length for sources close to
the plane of the sky, such as radio galaxies. I show that the recently
observed spectral index asymmetry can also be interpreted as an
orientation effect if the hotspots advance at speeds of v0.2c.
This supports the idea that double sources are intrinsically two-sided
and that the depolarization and spectral asymmetries are primarily due
to orientation. High flow velocities in the hotspots give a natural
explanation for the compactness asymmetry, and imply a spectral index
asymmetry for the hotspots themselves.
Key words: polarization - galaxies: active - galaxies: jets
- radio continuum: galaxies.
- Models of the depolarization asymmetry
- Fitting the depolarization data
- Spectral index asymmetry
- Hotspot asymmetries
This article appeared in Monthly Notices of the Royal Astronomical
Society, vol 256, pp. 281-290 (1992). Copyright Royal Astronomical
Peter Tribble, firstname.lastname@example.org