2004A&A...........R astro-ph/0312163
High-frequency polarization properties of southern Kuhr sources
R. Ricci, I. Prandoni, C. Gruppioni, R.J. Sault, G. De Zotti
We have carried out observations at 18.5 GHz with the Australia
Telescope Compact Array (ATCA) of 250 out of the 258 Southern
extragalactic sources in the complete 5 GHz 1 Jy sample by K\"uhr et
al. (1981). In this paper we focus on the polarization properties of
this sample, while other properties will be addressed in a future
paper. In our analysis we subdivide the sample into flat and steep
spectrum sources following Stickel et al. (1994) classification,
where spectral indices were measured between 2.7 and 5 GHz. The
polarized flux has been measured with a S/N > 5 for 170 sources (114
flat-spectrum and 56 steep-spectrum) and upper limits have been set
for additional 27 sources (12 flat-spectrum and 15 steep-spectrum).
The median polarization degree at 18.5 GHz for the flat-spectrum
sub-sample is \Pi_{18.5}\simeq 2.7%, about a factor of 2 higher than
at 1.4 GHz (\Pi_{1.4}\simeq 1.4%, based on NVSS data). For
flat-spectrum sources we find a weak correlation between \Pi_{18.5}
and the high frequency (5--18.5 GHz) spectral index. No evidences of
significant correlations of the polarization degree with other
source properties are found. The median value of \Pi_{18.5} for the
steep spectrum sources is \simeq 4.8%, but our sample might be
biased against extended sources. We find indications of a
correlation between \Pi_{18.5} and both the low frequency (1.4--5
GHz) and the high frequency (5--18.5 GHz) spectral indices. An
important application of this work is the possibility to estimate
the contamination of CMB polarization maps by extragalactic radio
sources. Our results indicate that such contamination is within the
range of estimates given by Mesa et al. (2002).