MEASUREMENT OF THE HUBBLE CONSTANT FROM X-RAY AND 2.1 MILLIMETER OBSERVATIONS OF ABELL 2163

摘要

We report 2.1 mm observations of the Sunyaev-Zeldovich (S-Z) effect; these observations confirm our previous detection of a decrement in the cosmic microwave background intensity toward the cluster Abell 2163. The S-Z data are analyzed using the relativistically correct expression for the Comp-tonization. We begin by assuming the intracluster (IC) gas to be isothermal at the emission-weighted average temperature determined by a combined analysis of the ASCA and Ginga X-ray satellite observations. The results of ROSAT/PSPC observations are used to determine an isothermal model for the S-Z surface brightness. Fitting to this model, we determine the peak Comptonization to be y_0 = 3.73_(-0.61)~(+0.47)x10~(-4). The uncertainty includes contributions due to statistical uncertainty in the detection, instrumental baseline, calibration, and density model. Combining the X-ray and S-Z measurements, we determine the Hubble constant to be H_0(q_0 = 1/2) = 60_(-23)~(+40) km s~(-1) Mpc~(-1), where the uncertainty is dominated by the systematic difference in the ASCA- and Ginga-determined IC gas temperatures. ASCA observations suggest the presence of a significant thermal gradient in the IC gas. We determine H_0 as a function of the assumed IC gas thermal structure. Using the ASCA-determined thermal structure and keeping the emission-weighted average temperature the same as in the isothermal case, we find H_0(q_0 = 1/2) = 78_(-28)~(+54) km s~(-1) Mpc~(-1). Including additional uncertainties due to cluster asphericity, peculiar velocity, IC gas clumping, and astrophysical confusion, we find H_0(q_0 =1/2) = 78_(-40)~(+60) km s~(-1) Mpc~(-1).