2016ApJ...826..146B

In this second paper on the entire virial region of the relaxed fossil cluster RXJ 1159+5531, we present a hydrostatic analysis of the azimuthally averaged hot intracluster medium (ICM) using the results of Su et al. For a model consisting of ICM, stellar mass from the central galaxy (BCG), and an NFW dark matter (DM) halo, we obtain a good description of the projected radial profiles of ICM emissivity and temperature that yield precise constraints on the total mass profile. The BCG stellar mass component is clearly detected with a K-band stellar mass-to-light ratio, {M}_*/L_{K}=0.61±0.11 {M}_☉/L_☉ , consistent with stellar population synthesis models for a Milky Way initial mass function. We obtain a halo concentration,
c_{200}=8.4±1.0 , and virial mass, {M}_{200}=(7.9±0.6)×{10}^{13} {M}_☉ . For its mass, the inferred concentration is larger than most relaxed halos produced in cosmological simulations with Planck parameters, consistent with RXJ 1159+5531 forming earlier than the general halo population. The baryon fraction at r₂₀₀, {f}_{b,200}=0.134±0.007 , is slightly below the Planck value (0.155) for the universe. However, when we take into account the additional stellar baryons associated with non-central galaxies and the uncertain intracluster light (ICL), {f}_{b,200} increases by ~0.015 , consistent with the cosmic value and therefore no significant baryon loss from the system. The total mass profile is nearly a power law over a large radial range (∼0.2-10 R_ e_), where the corresponding density slope α obeys the α-{R}_{e} scaling relation for massive early-type galaxies. Performing our analysis in the context of MOND still requires a large DM fraction ( 85.0 % ±2.5 % at r=100 kpc) similar to that obtained using the standard Newtonian approach. The detection of a plausible stellar BCG mass component distinct from the NFW DM halo in the total gravitational potential suggests that ∼{10}^{14} {M}_☉ represents the mass scale above which dissipation is unimportant in the formation of the central regions of galaxy clusters.