LIMITS ON THE PECULIAR VELOCITIES OF 2 DISTANT CLUSTERS USING THE KINEMATIC SUNYAEV-ZELDOVICH-EFFECT

We report millimeter-wavelength observations of the Sunyaev-Zeldovich (S-Z) effect in two distant galaxy clusters. A relativistically correc t analysis of the S-Z data is combined with the results of X-ray obser vations to determine the radial peculiar velocities (v(r)) of the clus ters. We observed Abell 2163 (z = 0.201) in three millimeter-wavelengt h bands centered at 2.1, 1.4, and 1.1 mm. We report a significant dete ction of the thermal component of the S-Z effect seen as both a decrem ent 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 astrophysica l confusion, a simultaneous fit to the data in all three bands gives v (r) = +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 detai led accounting of uncertainty, a simultaneous fit to the data in both bands gives v(r) = +170(-630)(+815) km s(-1). The limits on the peculi ar velocities of A2163 and A1689 correspond to deviations from the uni form Hubble flow of less than or similar to 2%-3%.