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Published April 11, 2013 | Published
Journal Article Open

The radio source count at 93.2 GHz from observations of 9C sources using AMI and CARMA


We present results from follow-up observations of a sample of 80 radio sources, originally detected as part of the 15.2-GHz Ninth Cambridge (9C) survey. The observations were carried out, close to simultaneously, at two frequencies: 15.7 GHz, using the Arcminute Microkelvin Imager (AMI) Large Array, and 93.2 GHz, using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). There is currently little direct information on the 90-GHz-band source count for S ≲ 1 Jy. However, we have used the measured 15.7-to-93.2-GHz spectral-index distribution and 9C source count to predict the differential source count at 93.2 GHz as 26 ± 4(S/Jy)^(−2.15) Jy^(−1) sr^(−1); our projection is estimated to be most accurate for 10 ≲ S ≲ 100 mJy. Our estimated differential count is more than twice the 90-GHz prediction made by Waldram et al.; we believe that this discrepancy is because the measured 43-GHz flux densities used in making their prediction were too low. Similarly, our prediction is significantly higher than that of Sadler et al. at 95 GHz. Since our spectral-index distribution is similar to the 20-to-95-GHz distribution measured by Sadler et al. and used in making their prediction, we believe that the difference is almost entirely attributable to the dissimilarity in the lower frequency counts used in making the estimates.

Additional Information

© 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2013 January 3. Received 2012 December 30; in original form 2012 April 30. First published online: February 1, 2013. We would like to thank the staff of the Mullard Radio Astronomy Observatory for maintaining and operating AMI.We are also grateful to the University of Cambridge and STFC for funding and supporting the LA. We thank Gianfranco de Zotti for kindly supplying his 93-GHz model source counts. Support for CARMA construction was derived from the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the James S. McDonnell Foundation, the Associates of the California Institute of Technology, the University of Chicago, the states of California, Illinois and Maryland, and the National Science Foundation. Ongoing CARMA development and operations are supported by the National Science Foundation under a cooperative agreement, and by the CARMA partner universities. IIS acknowledges a bursary from the Nuffield Foundation. MO, CRG, MPS, TWS and IHW acknowledge support from STFC studentships. YCP acknowledges support from the Rutherford Foundation PhD Scholarship.

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Published - MNRAS-2013-Davies-1961-9.pdf


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