The Australia Telescope 20-GHz ( AT20G ) Survey : the Bright Source Sample 2 O B S E RVAT I O N S
Massardi, Marcella ; Ekers, Ronald D ; Murphy, Tara ; et al. ; - ASI Sponsor
Jan - 2008
journal : Mon. Not. R. Astron. Soc
type: Article Journal
Abstract
The Australia Telescope 20GHz (AT20G) Survey is a blind surv ey of the whole South- ern sky at 20GHz (with follow-up observations at 4.8 and 8.6G Hz) carried out with the Australia Telescope Compact Array (ATCA) from 2004 to 20 07. The Bright Source Sample (BSS) is a complete flux-limited sub -sample of the AT20G Survey catalogue comprising 320 extragalactic ( | b | > 1 . 5 ◦ ) radio sources south of \delta = − 15 ◦ with S 20GHz > 0 . 50Jy. Of these, 218 have near simultaneous observations at 8 and 5GHz. In this paper we present an analysis of radio spectral proper ties in total inten- sity and polarisation, size, optical identifications and re dshift distribution of the BSS sources. The analysis of the spectral behaviour shows spect ral curvature in most sources with spectral steepening that increases at higher f requencies (the median spec- tral index \alpha , assuming S ∝ \nu \alpha , decreases from \alpha 8 . 6 4 . 8 = 0 . 11 between 4.8 and 8.6 GHz to \alpha 20 8 . 6 = − 0 . 16 between 8.6 and 20 GHz), even if the sample is dominated by fl at spectra sources (85 per cent of the sample has \alpha 20 8 . 6 > − 0 . 5). The almost simultaneous spectra in total intensity and polarisation allowed us a com parison of the polarised and total intensity spectra: polarised fraction slightly i ncreases with frequency, but the shapes of the spectra have little correlation. Optical i dentifications provided an estimation of redshift for 186 sources with a median value of 1.20 and 0.13 respectively for QSO and galaxies
keywords : active,cosmic microwave background,galaxies,radio continuum,surveys