2000ApJ...541...37P

We present multiwavelength observations of the Abell 1995 galaxy cluster. From an analysis of X-ray spectroscopy and imaging data, we derive the electron temperature, cluster core radius, and central electron number density. Using optical spectroscopy of 15 cluster members, we derive an accurate cluster redshift and velocity dispersion. Finally, the interferometric imaging of the Sunyaev-Zeldovich effect toward Abell 1995 at 28.5 GHz provides a measure of the integrated pressure through the cluster. The X-ray and Sunyaev-Zeldovich effect observations are combined to determine the angular diameter distance to the cluster of D_A=1294⁺²⁹⁴_–283⁺⁴³⁸_–458 Mpc (statistical followed by systematic uncertainty), implying a Hubble constant of H₀=52.2^+11.4_–11.9^+18.5_–17.7 km.s^–1.Mpc^–1 for Ω_M=0.3 and Ω_Λ=0.7. We find a best-fit H₀ of 46 km.s^–1.Mpc^–1 for the Ω_M=1 and Ω_Λ=0 cosmology, and 48 km.s^–1.Mpc^–1 for Ω_M=0.3 and Ω_Λ=0.0. The X-ray data are also used to derive a total cluster mass of M^HSE_tot(r₅₀₀)=5.18^+0.62_–0.48x10¹⁴ h^–1 M_☉; the optical velocity dispersion yields an independent and consistent estimate of M^virial_tot(r₅₀₀)=6.35^+1.51_–1.19x10¹⁴ h^–1 M_☉. Both of the total mass estimates are evaluated at a fiducial radius, r₅₀₀=830 h^–1 kpc, where the overdensity is 500 times the critical density. The total cluster mass is then combined with gas mass measurements to determine a cluster gas mass fraction of f_g=0.056^+0.010_–0.013 h^–3/2. In combination with recent baryon density constraints, the measured gas mass fraction yields an upper limit on the mass density parameter of Ω_M h^1/2≤0.34^+0.06_–0.05.