1999/04/27 by Maxim Markevitch, M. Markevitch, A. Vikhlinin +4 · 4 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1086/308124
published as Astrophys.J. 527 (1999) 545 · Latex, 9 pages, 6 figures, uses emulateapj.sty. Submitted to ApJ
arxiv created 1999/04/27 · openalex publication_date 1999/12/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We present maps and radial profiles of the gas temperature in the nearby galaxy clusters A2199 and A496, which have the most accurate ASCA spectral data of all hot clusters. X-ray images, temperature maps, and the presence of moderate cooling flows indicate that these clusters are relaxed and therefore can provide reliable X-ray mass measurements under the assumption of hydrostatic equilibrium and thermal pressure support. The average cluster temperatures corrected for the presence of cooling flows are 4.8 ± 0.2 and 4.7 ± 0.2 keV (90% errors), respectively, which are 10% higher than the wide-beam single-temperature fits. Outside the central cooling-flow regions and within r ≈ 0.7 h -1 Mpc covered by ASCA , the radial temperature profiles are similar to those of the majority of nearby relaxed clusters. They are accurately described by polytropic models with γ = 1.17 ± 0.07 for A2199 and γ = 1.24 for A496. We use these polytropic models to derive accurate total mass profiles. Within r = 0.5 h -1 Mpc, which corresponds to a radius of overdensity 1000, r 1000 , for these clusters (estimated from our mass profiles), the total mass values are × 10 14 and × 10 14 h -1 M ☉ . These values are 10% lower than those obtained assuming constant temperature. On the other hand, the values inside a gas core radius (0.07-0.13 h -1 Mpc) are a factor of ≳1.5 higher than the isothermal values. The gas mass fraction increases significantly with radius (by a factor of 3 between the X-ray core radius and r 1000 ) and at r 1000 reaches similar values of 0.057 ± 0.005 and 0.056 ± 0.006 h -3/2 for the two clusters, respectively. Our measured total mass profiles within r 1000 are remarkably well approximated by the Navarro, Frenk, & White "universal" profile. Since A2199 and A496 are typical relaxed clusters, the above findings should be relevant for most such systems. In particular, the observed similarity of the temperature profiles in nearby clusters appears to reflect the underlying "universal" dark matter profile. The upward revision of the mass values at small radii for the observed temperature profile compared with those derived assuming isothermality will resolve most of the discrepancy between the X-ray and strong lensing mass estimates.