| Detection of a CMB decrement towards the (1997) | |||||||||||||||
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| In a 15-GHz Ryle-Telescope observation of PC1643+4631 A & B, a pair of quasars at redshifts z = 3:79 and 3.83 separated by 198 00 on the sky, we find a decrement in the cosmic microwave background (CMB) of Gamma380 Sigma 64 ¯Jy in a 110 00 Theta 175 00 beam. Assuming this to be a Sunyaev-Zel'dovich effect due to an intervening cluster, the minimum magnitude of the central temperature decrement is 560 ¯K. A serendipitous ROSAT observation shows that there is no X-ray-luminous cluster in the direction of the decrement at z ! 1. The implied gas mass is ¸ ? 2 Theta 10 14 M fi (assuming a temperature of ¸ 5 keV), indicating a total mass of ? 10 15 M fi . This result demonstrates the existence of a massive system too distant to be detected by its emission, but which can be found via its imprint on the CMB. Subject headings: Cosmic microwave background---quasars:individual:PC1643+4631 A & B---galaxies:clusters 1. Introduction Clusters of galaxies are difficult to identify opt... | |||||||||||||||
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