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Description
The 9C (9th Cambridge) survey of radio sources with the Ryle Telescope at 15.2 GHz was set up to survey the fields of the cosmic microwave background telescope, the Very Small Array (VSA). In their first paper (Waldram et al. 2003, MNRAS, 342, 915), the authors described three regions of the survey, constituting a total area of 529 deg<sup>2</sup> to a completeness limit of ~ 25 mJy. In this follow-up, they present results from a series of deeper regions, constituting a total area of 115 deg<sup>2</sup> complete to ~ 10 mJy and of 29 deg<sup>2</sup> complete to ~ 5.5 mJy. The authors have investigated the source counts and the distributions of the 1.4 to 15.2 GHz spectral indices for these deeper samples. The whole catalog of 643 sources is contained in the present table. Down to their lower limit of 5.5 mJy, the authors detect no evidence for any change in the differential source count from the earlier fitted count above 25 mJy, n(S) = 51(S/Jy)<sup>-2.15</sup> Jy<sup>-1</sup> sr<sup>-1</sup>. They matched both their new and earlier catalogues with the NRAO VLA Sky Survey (NVSS) catalogue at 1.4 GHz and selected flux-limited samples at both 15 and 1.4 GHz. As they expected, they found that the proportions of sources with flat and rising spectra in the samples selected at 15 GHz are significantly higher than those in the samples selected at 1.4 GHz. In addition, for 15-GHz samples selected in three flux density ranges, they detect a significant shift in the median value of the 1.4 to 15.2 GHz spectral index: the higher the flux densities, the higher the proportions of sources with flat and rising spectra. In the area complete to ~ 10 mJy, the authors find five sources between 10 and 15 mJy at 15 GHz, amounting to 4.3 per cent of sources in this range, with no counterpart in the NVSS catalogue. This implies that, had they relied on the NVSS for locating their sources, they could have missed a significant proportion of them at low flux densities. These results illustrate the problems inherent in using a low-frequency catalog to characterize the source population at a much higher frequency and emphasize the value of a blind 15.2-GHz survey. This table was created in November 2010 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/MNRAS/404/1005">CDS catalog J/MNRAS/404/1005</a> file 9c_cont.dat. This is a service provided by NASA HEASARC .
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