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For refcode 1993A&A...267...31P:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1993A&A...267...31P Polarization properties at 1.4 GHz of low luminosity radio galaxies P. Parma, R. Morganti, A. Capetti, R.Fanti, and H.R. de Ruiter Istituto di Radioastronomia CNR, Via Irnerio 46, I-40126 Bologna, Italy Istituto di Fisica Generale, Universita di Torino, Via Giuria 1,I-10125 Torino, Italy Dipartimento di Fisica, Universita di Bologna, Via Irnerio 46,I-40126, Bologna, Italy Osservatorio Astronomico di Bologna, Via Zamboni, 33,I-40126 Bologna, Italy Received May 4, accepted July 17, 1992 Abstract. The 20 cm polarization properties of 65 low luminosity B 2 radio galaxies are discussed and in particular the polarization ratio of the radio lobes. It is argued that the polarization asymmetry at 20 cm can be used as a qualitative indicator of depolarization asymmetry. Thus, if the Laing-Garrington effect is also present in low luminosity radio galaxies, it may show up in the 20 cm data of the B 2 sample as an asymmetry in the lobe polarization. The polarization asymmetry we find in our sample is similar to that in the sample of radio galaxies of Garrington et al. with z < 1. Although the observed asymmetry is in general weak, it appears to be still present in the B 2 sample. This seems to imply that even at the low luminosities of B2 sources a small degree of beaming is required: in the Laing scenario the radio jet beamed towards the observer is seen through a smaller layer of a depolarizing halo than the radio jet pointed away from us. The jet velocities must be high enough to cause a Doppler difference in intensity between jet and counter jet. The inferred high velocities are in contrast with our current ideas about low luminosity galaxies (expected jet velocities are at most 10^4^km s^-1^). In most radio sources the radiojets are separated from the core by a gap in brightness. A statistically significant anti-correlation is found between the size of this gap and the fractional polarization of the corresponding lobe. It is difficult to find an explanation in the framework of Laing's beaming scenario, which leads us to suggest that a different mechanism (possibly intrinsic) is at work to produce depolarization asymmetries. Key words: radio galaxies - polarization
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