The 100-m Robert C. Byrd Green Bank Telescope ( GBT ) and the 40-m Owens Valley Radio Observatory ( OVRO ) telescope have been used to conduct a 31 GHz survey of 3 , 165 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 ( AGN ) with 1.4 GHz flux densities of 3 to 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 to 31 GHz spectral indices of these sources , we find a mean 31 to 1.4 GHz flux ratio of 0.110 \pm 0.003 corresponding to a spectral index of \alpha = -0.71 \pm 0.01 ( S _ { \nu } \propto \nu ^ { \alpha } ) ; 9.0 \pm 0.8 \% of sources have \alpha > -0.5 and 1.2 \pm 0.2 \% have \alpha > 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 \pm 1.7 ) { deg ^ { -2 } } ( S _ { 31 } / { 1 mJy } ) ^ { -0.80 \pm 0.07 } .
We also assess the contribution of mJy-level ( S _ { 1.4 GHz } < 3.4 { mJy } ) radio sources to the 31 GHz CMB power spectrum , finding a mean power of \ell ( \ell + 1 ) C ^ { src } _ { \ell } / ( 2 \pi ) = 44 \pm 14 { \mu K ^ { 2 } } and a 95 \% upper limit of 80 { \mu K ^ { 2 } } at \ell = 2500 .
Including an estimated contribution of 12 { \mu K ^ { 2 } } from the population of sources responsible for the turn-up in counts below S _ { 1.4 GHz } = 1 { mJy } this amounts to 21 \pm 7 \% of what is needed to explain the CBI high- \ell excess signal , 275 \pm 63 { \mu K ^ { 2 } } .
These results are consistent with other measurements of the 31 GHz point source foreground .