The enhancement and decrement of the Sunyaev-Zeldovich effect toward the ROSAT cluster RX J0658-5557

We report simultaneous observations of the X-ray cluster RX J0658-5557 at 1 .2 and 2 mm made with a double-channel photometer on the Swedish ESO Submil limeter Telescope (SEST) in search of Sunyaev-Zeldovich (SZ) effect. The SZ data were analyzed using the relativistically correct expression for the C omptonization, and we find (2.60 +/- 0.79) x 10(-4) from the detected decre ment, which is consistent with that computed using the X-ray (ROSAT and ASC A) observations. The uncertainty includes contributions from statistical un certainties in the detection, systematics, and calibration. The 1.2 mm chan nel data alone give rise to a larger Comptonization parameter; this result is discussed in terms of contamination from foreground sources and/or dust in the cluster or from a possible systematic effect. We then make use of a combined analysis of the ROSAT and ASCA X-ray satellite observations to det ermine an isothermal model for the SZ surface brightness. Since the cluster is asymmetrical and probably in a merging process, models are only approxi mate. The associated uncertainty can, however, be estimated by exploring a set of alternative models. We then find a factor of 1.3 for the global unce rtainty on the Comptonization parameter. Combining the SZ and the X-ray mea surements, we determine a value for the Hubble constant. The 2 mm data are consistent with H-0(q(0) = 1/2)= 53(-28)(+38) km s(-1) Mpc(-1), where the u ncertainty is dominated by the uncertainty in the models of the X-ray plasm a halo.