科研之友
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摘要
We present polarization data for 180 extragalactic sources extracted from the Australia Telescope 20 GHz (AT20G) survey catalogue and observed with the Australia Telescope Compact Array during a dedicated, high sensitivity run (sigma(P) similar to 1 mJy). For the sake of completeness, we extracted the polarization information for seven extended sources from the 9 yr Wilkinson Microwave Anisotropy Probe co-added maps at 23 GHz. The full sample of 187 sources constitutes a similar or equal to 99 per cent complete sample of extragalactic sources brighter than S-20GHz = 500 mJy at the selection epoch with declination delta %26lt; -30 degrees. The sample has a 91.4 per cent detection rate in polarization at similar to 20 GHz (94 per cent if considering the subsample of point-like sources). We have measurements also at 4.8 and 8.6 GHz within similar to 1 month of the 20 GHz observations for 172 sources to reconstruct the spectral properties of the sample in total intensity and in polarization: 143 of them have a polarization detection at all three frequencies. %26lt;br%26gt;We find that there is no statistically significant evidence of a relationship either between the fraction of polarization and frequency or between the fraction of polarization and the total intensity flux density. This indicates that Faraday depolarization is not very important above 4.8 GHz and that the magnetic field is not substantially more ordered in the regions dominating the emission at higher frequencies (up to 20 GHz). We estimate the distribution of the polarization fraction and the polarized flux density source counts at similar to 20 GHz.
- 出版日期2013-12
- 单位CSIRO
