The entire virial radius of the fossil cluster RXJ 1159 + 5531. II. Dark matter and baryon fraction
- Department of Physics and Astronomy, University of California at Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697-4575 (United States)
- INAF-IASF-Milano, Via E. Bassini 15, I-20133 Milano (Italy)
- Dipartimento di Fisica e Astronomia, Universita di Bologna, via Ranzani 1, 40126 Bologa (Italy)
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{sub ⋆}/L{sub K}=0.61±0.11 M{sub ⊙}/L{sub ⊙}, consistent with stellar population synthesis models for a Milky Way initial mass function. We obtain a halo concentration, c{sub 200}=8.4±1.0, and virial mass, M{sub 200}=(7.9±0.6)×10{sup 13} M{sub ⊙}. 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 r {sub 200}, f{sub 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{sub 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 {sub e}), where the corresponding density slope α obeys the α−R{sub 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{sup 14} M{sub ⊙} represents the mass scale above which dissipation is unimportant in the formation of the central regions of galaxy clusters.
- OSTI ID:
- 22868858
- Journal Information:
- Astrophysical Journal, Vol. 826, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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