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
CB3 0HA)
Accepted 1991 December 12. Received 1991 December 2; in original form
1991 August 20.
SUMMARY
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 v
0.2c.
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.
Contents:
- Introduction
- Models of the depolarization asymmetry
- Fitting the depolarization data
- Spectral index asymmetry
- Hotspot asymmetries
- Conclusions
This article appeared in Monthly Notices of the Royal Astronomical
Society, vol 256, pp. 281-290 (1992). Copyright Royal Astronomical
Society.
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Peter Tribble, peter.tribble@gmail.com