Issue |
A&A
Volume 427, Number 2, November IV 2004
|
|
---|---|---|
Page(s) | 465 - 483 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20040460 | |
Published online | 28 October 2004 |
The B3–VLA CSS sample *
IV. kpc-scale polarization properties
1
Dipartimento di Fisica, Universitá di Bologna, via Irnerio 46, 40126 Bologna, Italy
2
Istituto di Radioastronomia del CNR, via Gobetti 101, 40129 Bologna, Italy e-mail: m.branchesi@ira.cnr.it
3
Dipartimento di Astronomia, Universitá di Bologna, via Ranzani 1, 40127 Bologna, Italy
4
National Radio Astronomy Observatory, Charlottesville, USA
5
INAF - Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Strada 54, 09012 Capoterra, Italy
6
Istituto di Radioastronomia del CNR, CP 141, 96017 Noto SR, Italy
Received:
17
March
2004
Accepted:
23
July
2004
We discuss VLA polarization measurements at 8.5, 4.9 and 1.4 GHz
for the B3-VLA sample of Compact Steep-spectrum Sources (CSS). The
measurements at the two higher frequencies were presented in a
previous paper (Fanti et al. [CITE]), while those at 1.4 GHz
are from the NVSS.
The study of the fractional polarization as a function of wavelength shows a variety of behaviours not always
accounted for by the current simple models.
In a large fraction of sources the integrated rotation angle appears
to follow the law down to 1.4 GHz, although this
conclusion has to be treated with some care due to the small number of
polarization measurements.
For sources resolved at the two higher frequencies we find that a
number exhibit asymmetries in the 8.5 GHz fractional polarization,
in depolarization and rotation angle.
We discuss depolarization effects and rotation of the polarization
angle.
We find that Faraday depth effects are very strong within 2-3 kpc
of the nucleus, as found earlier by Cotton et al. ([CITE]).
A simple model for an external Faraday screen is able to account for
the gross observed features. We also find that the Rotation Measure and the Faraday Dispersion
appear to increase with the source red-shift.
Key words: galaxies: active / polarization / radio continuum: galaxies / quasars: general / ISM: structure
© ESO, 2004
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