Volume 406, Number 2, August I 2003
|Page(s)||579 - 592|
|Published online||17 November 2003|
Multi-frequency study of the B3-VLA sample
III. Polarisation properties
Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
2 Istituto di Radioastronomia del CNR, Via Gobetti 101, 40129 Bologna, Italy
3 ASTRON, Postbus 2, 7990 AA Dwingeloo, The Netherlands
4 Dipartimento di Fisica, Università di Bologna, Via Irnerio 46, 40126 Bologna, Italy
Corresponding author: U. Klein, firstname.lastname@example.org
Accepted: 19 May 2003
This paper is the third of a series, and presents the results of the linear polarisation of the B3-VLA sample, at 1.4, 2.7, 4.8 and 10.5 GHz. We find that flat-spectrum sources are significantly less polarised than the steep ones at 10.5 GHz. A trend is seen for sources with larger linear size to be more strongly polarised. Compact steep-spectrum sources (CSSs) exhibit much stronger depolarisation than non-CSSs. Flat-spectrum sources are characterized by almost constant, and low, degrees of polarisation over the whole wavelength range studied here. We add 143 new Rotation Measures to the available database published by Wielebinski & Krause (1993). An important result is that the decrease of the degree of polarisation is almost linear with wavelength and does not drop to zero at lower frequencies. This behaviour cannot be fitted by any existing model of external depolarisation or intrinsic Faraday dispersion. We consider an intrinsic process producing the observed depolarisation, involving three source components with different emissivities and Faraday depths, while the Faraday rotation must arise from a foreground screen, most likely Galactic in origin.
Key words: polarisation / surveys / radio continuum: galaxies
© ESO, 2003
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