Sunyaev-Zel'dovich effect

The 2 mm window is optimal to detect gamma-ray burst afterglows and the SZ-effect towards galaxy clusters. The most interesting SZ-observations in the coming years will be large-area ($>$100 square degrees) surveys to study the distribution of galaxy clusters at high redshifts. Such surveys are best done with 10m-class telescopes at 2 mm, for which the arcminute beam matches the typical cluster size. Dedicated SZ survey cameras are now being built for APEX (MPIfR/U.C.Berkeley) and for a new South Pole telescope (Chicago). HUMBA, a 19-element 2 mm bolometer array, was developed by the MPIfR for the IRAM 30 m telescope. In November 2001 it was successfully tested with the detection of a SZ decrement towards two clusters. HUMBA still falls short of its theoretical performance limit, and we hope to improve upon this with further modifications. It is hoped that HUMBA will be fully operational by mid 2003, and that in the future the number of beams can be increased to fill the available focal plane.