For refcode 2000MNRAS.311..825W: Retrieve 27 NED objects in this reference. Please click here for ADS abstract
NED Abstract
Copyright by Royal Astronomical Society.
2000MNRAS.311..825W
Constraints on the asymptotic baryon fractions of galaxy clusters at large
radii
XiangPing Wu and YanJie Xue
Accepted 1999 September 10. Received 1999 August 13; in original form 1999
June 28
ABSTRACT
While Xray measurements have so far revealed an increase in the volume
averaged baryon fractions f_b_(r) of galaxy clusters with cluster radii r,
f_b_(r) should asymptotically reach a universal value f_b_({infinity})=
f_b_, provided that clusters are representative of the Universe. In the
framework of hydrostatic equilibrium for intracluster gas, we have derived
the necessary conditions for f_b_({infinity})= f_b_. The Xray surface
brightness profile described by the {beta} model and the temperature
profile approximated by the polytropic model should satisfy {gamma} ~2(1
1/3{beta}) and {gamma} ~1+1/3{beta} for {beta} < 1 and {beta} > 1,
respectively, which sets a stringent limit to the polytropic index: {gamma}
< 4/3. In particular, a mildly increasing temperature with radius is
required if the observationally fitted {beta} parameter is in the range
1/3<{beta}<2/3. It is likely that a reliable determination of the universal
baryon fraction can be achieved in the small {beta} clusters because the
disagreement between the exact and asymptotic baryon fractions for clusters
with {beta}>2/3 breaks down at rather large radii (>~30rc) where
hydrostatic equilibrium has probably become inapplicable. We further
explore how to obtain the asymptotic value f_b_({infinity}) of the baryon
fraction from the Xray measurement made primarily over the finite central
region of a cluster. We demonstrate our method using a sample of 19 strong
lensing clusters, which enables us to place a useful constraint on
f_b_({infinity}):0.094+/0.035<= f_b_({infinity})<=0.41+/0.18,
corresponding to a cosmological density parameter 0.122+/0.069<={OMEGA}_M_
<= 0.53+/0.28 for H_0_ = 50 km s^1^ Mpc^1^. An optimal estimate of
f_b_({infinity}) based on three cooling flow clusters with b<1/2 in our
lensing cluster sample yields <f_b_({infinity})> = 0.142+/0.007 or
{OMEGA}_M_ = 0.35+/0.09.
Keywords: galaxies: clusters: general  intergalactic medium  cosmology:
theory  Xrays: galaxies
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