For refcode 2008MNRAS.383..879A: Retrieve 42 NED objects in this reference. Please click here for ADS abstract
NED Abstract
Copyright by Royal Astronomical Society.
2008MNRAS.383..879A
Improved constraints on dark energy from Chandra Xray observations of the
largest relaxed galaxy clusters
S. W. Allen, D. A. Rapetti, R. W. Schmidt, H. Ebeling, R. G. Morris and A.
C. Fabian
Abstract. We present constraints on the mean matter density, {OMEGA}_m_,
dark energy density, {OMEGA}_DE_, and the dark energy equation of state
parameter, w, using Chandra measurements of the Xray gas mass fraction
(f_gas_) in 42 hot (kT > 5 keV), Xray luminous, dynamically relaxed
galaxy clusters spanning the redshift range 0.05 < z < 1.1. Using only
the f_gas_ data for the six lowest redshift clusters at z < 0.15, for
which dark energy has a negligible effect on the measurements, we
measure {OMEGA}_m_ = 0.28 +/ 0.06 (68 per cent confidence limits, using
standard priors on the Hubble constant, H_0_, and mean baryon density,
{OMEGA}_b_ h^2^). Analysing the data for all 42 clusters, employing only
weak priors on H_0_ and {OMEGA}_b_ h^2^, we obtain a similar result on
{OMEGA}_m_ and a detection of the effects of dark energy on the
distances to the clusters at ~99.99 per cent confidence, with
{OMEGA}_DE_ = 0.86 +/ 0.21 for a nonflat {LAMBDA}CDM model. The
detection of dark energy is comparable in significance to recent type Ia
supernovae (SNIa) studies and represents strong, independent evidence
for cosmic acceleration. Systematic scatter remains undetected in the
f_gas_ data, despite a weighted mean statistical scatter in the distance
measurements of only ~5 per cent. For a flat cosmology with a constant
dark energy equation of state, we measure {OMEGA}_m_ = 0.28 +/ 0.06 and
w = 1.14 +/ 0.31. Combining the f_gas_ data with independent
constraints from cosmic microwave background and SNIa studies removes
the need for priors on {OMEGA}_b_ h^2^ and H_0_ and leads to tighter
constraints: {OMEGA}_m_ = 0.253 +/ 0.021 and w = 0.98 +/ 0.07 for the
same constantw model. Our most general analysis allows the equation of
state to evolve with redshift. Marginalizing over possible transition
redshifts 0.05 < z_t_ < 1, the combined f_gas_ + CMB + SNIa data set
constrains the dark energy equation of state at late and early times to
be w_0_ = 1.05 +/ 0.29 and w_et_ = 0.83 +/ 0.46, respectively, in
agreement with the cosmological constant paradigm. Relaxing the
assumption of flatness weakens the constraints on the equation of state
by only a factor of ~2. Our analysis includes conservative allowances
for systematic uncertainties associated with instrument calibration,
cluster physics and data modelling. The measured small systematic
scatter, tight constraint on {OMEGA}_m_ and powerful constraints on dark
energy from the f_gas_ data bode well for future dark energy studies
using the next generation of powerful Xray observatories, such as
ConstellationX.
Key words: cosmic microwave background, cosmological parameters, cosmology:
observations, dark matter, distance scale, Xrays: galaxies: clusters
Retrieve 42 NED objects in this reference. Please click here for ADS abstract
