Issue |
A&A
Volume 436, Number 2, June III 2005
|
|
---|---|---|
Page(s) | 411 - 416 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20041851 | |
Published online | 30 May 2005 |
Evidence for new physics from clusters?
1
LATT, 14 avenue Edouard Belin, 31400 Toulouse, France e-mail: alain.blanchard@ast.obs-mip.fr
2
LATT, 14 avenue Edouard Belin, 31400 Toulouse, France e-mail: douspis@ast.obs-mip.fr
Received:
16
August
2004
Accepted:
11
February
2005
The abundance of local clusters is a traditional way to
derive the amplitude of matter fluctuations, commonly specified by
, but which suffers from a systematic uncertainty arising
from the lack of accurate knowledge of the mass temperature
relation. In the present work, by assuming that the observed
baryon content of clusters is representative of the universe, we
show that the mass temperature relation (
) can be specified
for any cosmological model. WMAP constraints on the baryonic
content of the Universe and the
relation allows one
further improvement in tightening this
relation. This
approach allows one to remove most of the above uncertainty, and to
provide an estimation of
whose uncertainty is
essentially statistical. The values we obtain are fortuitously
almost independent of the matter density of the Universe
(
) with an accuracy better than 5%. Quite
remarkably, the amplitude of matter fluctuations can be also
tightly constrained to similar accuracy from existing CMB
measurements alone, once the dark matter content is specified.
However, the amplitude inferred in this way in a concordance model
(
) is significantly larger than the value derived from
the above method based on X-ray clusters. Such a discrepancy would
almost disappear if the actual optical thickness of the Universe
was 0 but could also be alleviated from more exotic solutions: for
instance the existence of a new non-baryonic light dark component
in the Universe as massive neutrinos, with
. However, recent other indications of
favor
a high normalization. In this case, the assumption that the
baryonic content observed in clusters actually reflects the
primordial value has to be relaxed: either there exists a large
baryonic dark component in the Universe with
or baryons in clusters have
undergone a large depletion during the formation of these
structures. We concluded that the baryon fraction in clusters is
not representative and therefore that an essential piece of the
physics of baryons in clusters is missing in standard structure
formation scenario.
Key words: cosmology: observations / galaxies: clusters: general / cosmological parameters
© ESO, 2005
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