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Title: ON THE CLUSTER PHYSICS OF SUNYAEV-ZEL'DOVICH AND X-RAY SURVEYS. III. MEASUREMENT BIASES AND COSMOLOGICAL EVOLUTION OF GAS AND STELLAR MASS FRACTIONS

Gas masses tightly correlate with the virial masses of galaxy clusters, allowing for a precise determination of cosmological parameters by means of X-ray surveys. However, the gas mass fractions (f{sub gas}) at the virial radius (R{sub 200}) derived from recent Suzaku observations are considerably larger than the cosmic mean, calling into question the accuracy of cosmological parameters. Here, we use a large suite of cosmological hydrodynamical simulations to study measurement biases of f{sub gas}. We employ different variants of simulated physics, including radiative gas physics, star formation, and thermal feedback by active galactic nuclei, which we show is able to arrest overcooling and to result in constant stellar mass fractions for redshifts z < 1. Computing the mass profiles in 48 angular cones, we find anisotropic gas and total mass distributions that imply an angular variance of f{sub gas} at the level of 30%. This anisotropy originates from the recent formation epoch of clusters and from the strong internal baryon-to-dark-matter density bias. In the most extreme cones, f{sub gas} can be biased high by a factor of two at R{sub 200} in massive clusters (M{sub 200} ∼ 10{sup 15} M{sub ☉}), thereby providing an explanation for high f{sub gas} measurementsmore » by Suzaku. While projection lowers this factor, there are other measurement biases that may (partially) compensate. At R{sub 200}, f{sub gas} is biased high by 20% when assuming hydrostatic equilibrium masses, i.e., neglecting the kinetic pressure, and by another ∼10%-20% due to the presence of density clumping. At larger radii, both measurement biases increase dramatically. While the cluster sample variance of the true f{sub gas} decreases to a level of 5% at R{sub 200}, the sample variance that includes both measurement biases remains fairly constant at the level of 10%-20%. The constant redshift evolution of f{sub gas} within R{sub 500} for massive clusters is encouraging for using gas masses to derive cosmological parameters, provided the measurement biases can be controlled.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. Department of Physics, McWilliams Center for Cosmology, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213 (United States)
  2. Canadian Institute for Theoretical Astrophysics, 60 St George, Toronto ON, M5S 3H8 (Canada)
  3. Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany)
  4. Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544 (United States)
Publication Date:
OSTI Identifier:
22270579
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 777; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANISOTROPY; COMPUTERIZED SIMULATION; COSMOLOGY; DENSITY; GALAXY CLUSTERS; GALAXY NUCLEI; HYDRODYNAMICS; MASS; MASS DISTRIBUTION; NONLUMINOUS MATTER; RED SHIFT; STAR EVOLUTION; STARS; UNIVERSE; X RADIATION