Issue |
A&A
Volume 383, Number 2, FebruaryIV 2002
|
|
---|---|---|
Page(s) | 450 - 471 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20011750 | |
Published online | 15 February 2002 |
Competition between shocks and entropy floor: Unifying groups and clusters of galaxies
1
Department of Physics & Astronomy, University of Leicester, 1 University Road, Leicester LE1 7RH, UK e-mail: ssa@star.le.ac.uk
2
Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
Corresponding author: S. Dos Santos, dore@iap.fr
Received:
27
June
2001
Accepted:
6
December
2001
Semi-analytic models of X-ray clusters and groups of galaxies,
relying on the idea that there was a non-gravitational energy injection in
these systems, are able to reproduce many observed correlations, in
particular the relation and the “central entropy floor” in
groups. Limiting models exist which describe the behaviour of clusters and
groups separately, but no analytic modeling has yet been found to unify both
mass ranges. It is the aim of this paper to provide such an analytic
model. Our description relies on a now standard description of the shock
thought to occur in these systems near the virial radius (Cavaliere et al. [CITE]), the
isothermality and spherical symmetry of the intracluster medium, as well as
the reinterpretation of observed quantities (like the X-ray luminosity, the
gas mass MICM and the central SZ effect y0) in terms of the specific
entropy. This allows the derivation of analytic expressions for several
observed correlations (
,
,
,...) and their
normalisation encompassing both the group and the cluster regimes. The
analytic predictions compare very well with observations, as well as with
more elaborated semi-analytic schemes. This agreement allows a
reinterpretation of the
relation (via the quantity
) and
the
relation (via
) as indirect measures of the
non-gravitational entropy content of groups and clusters of galaxies. We
emphasize the need for shock heating, even in the group mass range:
shocks can not be completely suppressed in groups (and thus groups can
not be entirely isentropic) unless an unacceptably high entropy floor is
needed in order to break the self-similarity in the
relation. Our
model shows that the normalisation of the entropy after the shock (which is
mass-dependent) is a key ingredient and that this quantity alone can
explain the shape of the observed correlations between integrated X-ray and
SZ quantities over and below 2 keV.
Key words: hydrodynamics / shock waves / galaxies: clusters: general / X-rays: galaxies: clusters / cosmology: large-scale structure of Universe
© ESO, 2002
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