Abstract
We report millimeter-wavelength observations of the Sunyaev-Zeldovich (S-Z) effect in two distant galaxy clusters. A relativistically correct analysis of the S-Z data is combined with the results of X-ray observations to determine the radial peculiar velocities (vr) of the clusters. We observed Abell 2163 (z = 0.201) in three millimeter-wavelength bands centered at 2.1, 1.4, and 1.1 mm. We report a significant detection of the thermal component of the S-Z effect seen as both a decrement in the brightness of the CMB at 2.1 mm and as an increment at 1.1 mm. Including uncertainties due to the calibration of the instrument, distribution and temperature of the intracluster gas, and astrophysical confusion, a simultaneous fit to the data in all three bands gives vr=+490−880+1370 km s-1 at 68% confidence. We observed Abell 1689 (z = 0.181) in the 2.1 and 1.4 mm bands. Including the same detailed accounting of uncertainty, a simultaneous fit to the data in both bands gives vr=+170−630+815 km s-1. The limits on the peculiar velocities of A2163 and A1689 correspond to deviations from the uniform Hubble flow of ≲2%-3%.