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Published October 20, 2009 | Published
Journal Article Open

A 31 GHz Survey of Low-Frequency Selected Radio Sources


The 100 m Robert C. Byrd Green Bank Telescope and the 40 m Owens Valley Radio Observatory telescope have been used to conduct a 31 GHz survey of 3165 known extragalactic radio sources over 143 deg^2 of the sky. Target sources were selected from the NRAO VLA Sky Survey in fields observed by the Cosmic Background Imager (CBI); most are extragalactic active galactic nuclei (AGNs) with 1.4 GHz flux densities of 3-10 mJy. The resulting 31 GHz catalogs are presented in full online. Using a maximum-likelihood analysis to obtain an unbiased estimate of the distribution of the 1.4-31 GHz spectral indices of these sources, we find a mean 31-1.4 GHz flux ratio of 0.110 ± 0.003 corresponding to a spectral index of α = –0.71 ± 0.01 (S_ν ∝ ν^α); 9.0% ± 0.8% of sources have α > –0.5 and 1.2% ± 0.2% have α > 0. By combining this spectral-index distribution with 1.4 GHz source counts, we predict 31 GHz source counts in the range 1 mJy < S_(31) < 4 mJy, N(>S_(31)) = (16.7 ± 1.7) deg^(-2)(S_(31)/1 mJy)^(–0.80±0.07). We also assess the contribution of mJy-level (S_(1.4 GHz) < 3.4 mJy) radio sources to the 31 GHz cosmic microwave background power spectrum, finding a mean power of ℓ(ℓ + 1)C^(src)_ℓ /(2π) = 44 ± 14 μK^2 and a 95% upper limit of 80 μK^2 at ℓ = 2500. Including an estimated contribution of 12 μK^2 from the population of sources responsible for the turn-up in counts below S_(1.4 GHz) = 1 mJy, this amounts to 21% ± 7% of what is needed to explain the CBI high-ℓ excess signal, 275 ± 63 μK^2. These results are consistent with other measurements of the 31 GHz point-source foreground.

Additional Information

© 2009 American Astronomical Society. Received 2009 February 2; accepted 2009 August 26; published 2009 October 2. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We thank the GBT and OVRO science and engineering staff for outstanding contributions to both survey projects and acknowledge support from NSF grants AST-9413935, AST-9802989, AST-0098734, and AST0206416. We thank Gianfraco deZotti for providing us with his most recent 30 GHz source count model; Dan Marrone for providing the SZA window functions; Jim Condon, Bill Cotton, Mike Jones, and Angela Taylor for helpful discussions; and Rachel Rosen for carefully proofreading the manuscript. We thank Liz Waldram and Guy Pooley for providing unpublished source size information from the 9C survey. Finally, we thank an anonymous referee for thorough comments which helped to improve the paper.

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Published - Mason2009p6133Astrophys_J.pdf


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