Measurement of the Hubble Constant from X‐Ray and 2.1 Millimeter Observations of Abell 2163

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Abstract
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 Comptonization. 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 y0 = 3.73+ 0.47−0.61×10−4. 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 H0(q0=½)=60+ 40−23 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 H0 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 H0(q0 = ½) = 78+ 54−28 km s-1 Mpc-1. Including additional uncertainties due to cluster asphericity, peculiar velocity, IC gas clumping, and astrophysical confusion, we find H0(q0=½)=78+ 60−40 km s-1 Mpc-1.
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