Trouble for blind SZ surveys?

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  • 24 February 2004
Abstract
The Sunyaev-Zel'dovich (SZ) effect of galaxy clusters is a tool to measure three quantities: Compton parameter, electron temperature, and cluster peculiar velocity. However, a major problem is non-removable (or non-removed) contamination by astrophysical sources which emit in the SZ frequencies. This includes interstellar dust emission, infra-red (IR) galaxies and radio sources. Such contaminations induce systematic shifts in the three SZ parameters. In the present study, we carefully analyse the non-removable dust, IR galaxies and radio sources, and estimate how big the induced systematic errors are for future planned SZ surveys (namely Planck Surveyor, ACT and SPT). We find that the interstellar dust emission is not a major contaminant for the SZ measurement. Unfortunately, the IR and radio source-induced systematic errors may be extremely large. In particular the intra-cluster temperature and peculiar velocity are determined completely incorrectly for Planck, ACT and SPT experiments, implying that the planned SZ surveys will not be able to extract the peculiar velocities and temperatures of clusters using SZ observations only. The Compton parameter is also affected by the astrophysical contaminations. The systematic errors in this case are a factor of 2 to 5 times larger than the expected statistical error-bar for Planck, and a factor of tens for SPT. For ACT, the statistical error-bars are larger than the previous two experiments, and therefore the systematic shifts remain within about 50% of the statistical errors. We have thus shown that the systematic errors due to contaminating astrophysical emissions can be significantly larger than the statistical errors, which potentially is disastrous for future survey experiments, and must be considered very seriously.

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