SIMBAD references

We have observed 250 of the 258 southern sources in the complete 5GHz 1Jy sample by Kuehr et al. (1981A&AS...45..367K) using the Australia Telescope Compact Array (ATCA) at 18.5GHz. This paper focuses on the polarization properties of this sample, while other properties will be addressed in a future paper. The analysis subdivides the sample into flat and steep spectrum sources using the classification of Stickel et al. (1994A&AS..105..211S), where spectral indices were measured between 2.7 and 5GHz. The polarized flux has been measured with a S/N>5 for 170 sources (114 flat-spectrum and 56 steep-spectrum). Upper limits have been set for additional 27 sources (12 flat-spectrum and 15 steep-spectrum). The median fractional polarization at 18.5GHz for the flat-spectrum sub-sample is Π_18.5≃2.7%, which is about a factor of 2 higher than at 1.4GHz (Π_1.4≃1.4%, based on NVSS data). No evidence was found of significant correlations of the fractional polarization with other source properties. The median value of Π_18.5 for the steep spectrum sources is ≃4.8%, but our sample might be biased against extended sources. We find some correlation between Π_18.5 and both the low-frequency (1.4-5GHz) and the high-frequency (5-18.5GHz) spectral indices. An important application of this work is in estimating the contamination of CMB polarization maps by extragalactic radio sources. Our results indicate that such contamination is within that estimated by Mesa et al. (2002A&A...396..463M).