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Session 19 - Source Surveys, Galaxy Surveys, Distance Scale II.
Display session, Wednesday, January 07
Exhibit Hall,

[19.06] Observations of Radio Sources towards Galaxy Clusters at 28.5 GHz

A. R. Cooray (U. Chicago), L. Grego (U. Chicago/Caltech), W. L. Holzapfel (U. Chicago), M. Joy (NASA MSFC), J. E. Carlstrom (U. Chicago)

We present serendipitous observations of radio sources at 28.5 GHz (1 cm), which resulted from our program to image thermal Sunyaev-Zeldovich (SZ) effect in 55 galaxy clusters. In a total area of \sim 0.8^\circ sq., we find \sim 60 radio sources with fluxes down to \sim 0.4 mJy (> 4 \sigma), and within 250'' from the cluster center. Typical synthesized beam sizes in our images range from 12" to 25". The spectral indices (S \propto \nu^-\alpha) of 42 sources with published low frequency flux densities range from -0.8 \lesssim \alpha \lesssim 1.7 with a mean of 0.74 \pm 0.10. We find 3 to 5 times more sources than one would expect based on a low frequency survey in areas without galaxy clusters, which cannot be accounted through gravitational lensing of a background radio population by cluster potentials. Therefore, a large number of sources in our sample should be associated with galaxy clusters. For the 28.5 GHz radio source sample, the differential source count is flatter than what is expected for a nonevolving Euclidean population. For the cluster Abell 2218, the presence of unsubtracted radio sources with S_28.5 GHz \leq 1 mJy (\sim 9 \sigma), only contribute to temperature fluctuations at a level of \Delta T \sim 10 to 25 \muK. The corresponding error due to radio point source contamination in the Hubble constant derived through a combined analysis of 28.5 GHz SZ images and X-ray emission observations ranges from 1% to 6%.

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