The following document lists the file abstract/IMCHARDY_1236.abs
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As the microwave background (MWB) photons travel towards us through rich clusters of galaxies, they are scattered to higher energies by the hot gas in the clusters. The resulting spectral distortion is called the Sunyaev-Zeldovich (SZ) effect and consists of a decrement in the MWB intensity in the direction of the cluster relative to the general background at wavelengths >1.4mm and an increment at wavelengths <1.4mm. The cosmological importance of the SZ effect is that, when coupled with X-ray observations of the hot scattering gas, it is possible to deduce the scale size of the universe, ie the Hubble constant, H_0. With the advent of the imaging sub-millimetre array, SCUBA, on the James Clerk Maxwell Telescope (JCMT) it will soon be possible to make observations of the SZ effect in the increment regime, where the spectral distortion should be large. However there have recently been some indications that clusters of galaxies may contain large amounts (10^9 solar massess) of very cool dust (temperatures of 10-30 K). Such dust would dominate the cluster emission at 200 microns and, although largely undetectable by IRAS, could also radiate noticeably in the sub-millimetre waveband and so could confuse observations of the SZ increment. We therefore propose ISOPHOT 200 observations, through 3 filters, to search for possible dust emission from a sample of SZ candidate clusters, and to measure its temperature, in order to determine whether dust may confuse future determinations of H_0.