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The Entire Virial Radius of the Fossil Cluster RXJ1159+5531: II. Dark Matter and Baryon Fraction

May 9, 2016
15 pages
Published in:
  • Astrophys.J. 826 (2016) 2, 146
  • Published: Jul 27, 2016
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Abstract: (IOP)
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⋆/LK=0.61±0.11 M⊙/L⊙{M}_{\star }/{L}_{K}=0.61\pm 0.11\,{M}_{\odot }/{L}_{\odot }, consistent with stellar population synthesis models for a Milky Way initial mass function. We obtain a halo concentration, c200=8.4±1.0{c}_{200}=8.4\pm 1.0, and virial mass, M200=(7.9±0.6)×1013 M⊙{M}_{200}=(7.9\pm 0.6)\times {10}^{13}\,{M}_{\odot }. 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 (200), fb,200=0.134±0.007{f}_{{\rm{b,200}}}=0.134\pm 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), fb,200{f}_{{\rm{b,200}}} increases by ≈0.015\approx 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−Re\alpha -{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%85.0 \% \pm 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 ∼1014 M⊙\sim {10}^{14}\,{M}_{\odot } represents the mass scale above which dissipation is unimportant in the formation of the central regions of galaxy clusters.
Note:
  • 15 pages, 7 figures. Accepted for Publication in the Astrophysical Journal
  • dark matter
  • galaxies: clusters: individual
  • galaxies: clusters: intracluster medium
  • X-rays: galaxies: clusters
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