OBSERVATIONS OF THE SUNYAEV-ZELDOVICH EFFECT AT HIGH ANGULAR RESOLUTION TOWARDS THE GALAXY CLUSTERS A665, A2163 AND CL0016+16

We report on the first observation of the Sunyaev-Zel'dovich (SZ) effe ct, a distortion of the Cosmic Microwave Background radiation (CMB) by hot electrons in clusters of galaxies, with the Diabolo experiment at the IRAM 30 m telescope. Diabolo is a dual-channel 0.1 K bolometer ph otometer dedicated to the observation of CMB anisotropies at 2.1 and 1 .2 mm. A significant brightness decrement in the 2.1 mm channel is det ected in the direction of three clusters (Abell 665, Abell 2163 and CL 0016+16). With a 30 arcsec beam and 3 arcmin beamthrow, this is the hi ghest angular resolution observation to date of the SZ effect. Interle aving integrations on targets and on nearby blank fields have been per formed in order to check and correct for systematic effects. Gas masse s can be directly inferred from these observations. (C) 1998 Elsevier Science B.V. All rights reserved.