paper

X-ray Constraints on the Intrinsic Shapes and Baryon Fractions of Five Abell Clusters

arXiv:astro-ph/9504049 · doi:10.1086/176753

Abstract

We analyzed ROSAT PSPC images of the bright, nearby galaxy clusters A401, A1656 (Coma), A2029, A2199, and A2256 to constrain their intrinsic shapes and baryon fractions. Following Buote & Tsai we probed the aggregate structure of the clusters on scales Mpc to reduce effects of possible substructure on smaller scales ( a few hundred kpc). The ellipticities of the X-ray isophotes are typically and display negative radial gradients significant (except Coma). By assuming hydrostatic equilibrium and a variety of mass models we obtain ellipticities for isothermal models of the total gravitating matter of the clusters; the constraints change by upon consideration of the small temperature gradients shown by ASCA to be typical for rich clusters; the observed X-ray ellipticity gradients require that mass models with constant ellipticity have steep density profiles, . Estimates of the gas masses are highly insensitive to the ellipticities of the X-ray isophotes. The clusters in our sample have increasing fractions of gas mass to total mass with radius and have within a radius Mpc, in excellent agreement with the results of White & Fabian and the Baryon Catastrophe proposed by White et al. (1993). Finally, the ellipticities of the dark matter distributions are essentially identical to and are consistent with the shapes of dark halos predicted by N-body simulations and the shapes of the galaxy isopleths in the clusters in contrast to our previous conclusions using {\it Einstein} data.

29 pages (2 figures), PostScript, to appear in ApJ on February 1, 1996. No changes to the text -- the publication date given before was incorrect

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