THE ENHANCEMENT AND DECREMENT OF THE SUNYAEV-ZELDOVICH EFFECT TOWARD THE ROSAT CLUSTER RX J0658-5557

摘要

We report simultaneous observations of the X-ray cluster RX J0658--5557 at l.2 and 2 mm made with a double-channel photometer on the Swedish ESO Submillimeter Telescope (SEST) in search of Sunyaev-Zeldovich (SZ) effect. The SZ data were analyzed using the relativistically correct expression for the Comptonization, and we find (2.60 +- 0.79) x 10~(-4) from the detected decrement, which is consistent with that computed using the X-ray (ROSAT and ASCA) observations. The uncertainty includes contri- butions from statistical uncertainties in the detection, systematics, and calibration. The 1.2 mm channel data alone give rise to a larger Comptonization parameter; this result is discussed in terms of contami- nation 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 determine an isothermal model for the SZ surface brightness. Since the cluster is asymmetrical and probably in a merging process, models are only approximate. 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 uncertainty on the Comptonization parameter. Combining the SZ and the X-ray measurements, we determine a value for the Hubble constant. The 2 mm data are consistent with Ho(qo = 0.5) = 53_28~38 km s~(-1) Mpc~(-1), where the uncertainty is dominated by the uncertainty in the models of the X-ray plasma halo.