14 research outputs found
The power spectrum amplitude from clusters revisited: σ8 using simulations with preheating and cooling
The amplitude of density perturbations, for the currently-favoured CDM cosmology, is constrained using the observed properties of galaxy clusters. The catalogue used is that of Ikebe et al. The relation of cluster temperature to mass is obtained via N-body/hydrodynamical simulations including radiative cooling and pre-heating of cluster gas, which we have previously shown to reproduce well the observed temperature–mass relation in the innermost parts of clusters. We generate and compare mock catalogues via a Monte Carlo method, which allows us to constrain the relation between X-ray temperature and luminosity, including its scatter, simultaneously with cosmological parameters. We find a luminosity–temperature relation in good agreement with the results of Ikebe et al., while for the matter power spectrum normalization, we find σ8 = 0.78+0.30 −0.06 at 95 per cent confidence for 0 = 0.35. Scaling to the Wilkinson Microwave Anisotropy Probe central value of 0 = 0.27 would give a best-fitting value of σ8 ≃ 0.9
Can simulations reproduce the observed temperature-mass relation for clusters of galaxies?
It has become increasingly apparent that traditional hydrodynamical
simulations of galaxy clusters are unable to reproduce the observed properties
of galaxy clusters, in particular overpredicting the mass corresponding to a
given cluster temperature. Such overestimation may lead to systematic errors in
results using galaxy clusters as cosmological probes, such as constraints on
the density perturbation normalization sigma_8. In this paper we demonstrate
that inclusion of additional gas physics, namely radiative cooling and a
possible preheating of gas prior to cluster formation, is able to bring the
temperature-mass relation in the innermost parts of clusters into good
agreement with recent determinations by Allen, Schmidt & Fabian using Chandra
data.Comment: 5 pages, submitted to MNRA
Evolution of X-ray cluster scaling relations in simulations with radiative cooling and non-gravitational heating
We investigate the redshift dependence of X-ray cluster scaling relations
drawn from three hydrodynamic simulations of the LCDM cosmology: a Radiative
model that incorporates radiative cooling of the gas, a Preheating model that
additionally heats the gas uniformly at high redshift, and a Feedback model
that self-consistently heats cold gas in proportion to its local star-formation
rate. While all three models are capable of reproducing the observed local
Lx-Tx relation, they predict substantially different results at high redshift
(to z=1.5), with the Radiative, Preheating and Feedback models predicting
strongly positive, mildly positive and mildly negative evolution, respectively.
The physical explanation for these differences lies in the structure of the
intracluster medium. All three models predict significant temperature
fluctuations at any given radius due to the presence of cool subclumps and, in
the case of the Feedback simulation, reheated gas. The mean gas temperature
lies above the dynamical temperature of the halo for all models at z=0, but
differs between models at higher redshift with the Radiative model having the
lowest mean gas temperature at z=1.5.
We have not attempted to model the scaling relations in a manner that mimics
the observational selection effects, nor has a consistent observational picture
yet emerged. Nevertheless, evolution of the scaling relations promises to be a
powerful probe of the physics of entropy generation in clusters. First
indications are that early, widespread heating is favored over an extended
period of heating that is associated with galaxy formation.Comment: Accepted for publication in ApJ. Minor changes following referee's
comment
The Effect of Cooling and Preheating on the X-ray Properties of Clusters of Galaxies
We calculate X-ray properties of present-day galaxy clusters from
hydrodynamical cosmological simulations of the LCDM cosmology and compare these
with recent X-ray observations. Results from three simulations are presented,
each of which uses the same initial conditions: a standard adiabatic,
Non-radiative model, a Radiative model that includes radiative cooling of the
gas, and a Preheating model that also includes cooling but in addition
impulsively heats the gas prior to cluster formation. At the end of the
simulations, the global cooled baryon fractions in the latter two runs are 15
per cent and 0.4 per cent respectively which bracket the recent result from the
K-band luminosity function. We construct cluster catalogues which consist of
over 500 clusters and are complete in mass down to 1.18*10^{13} Msun/h. While
clusters in the Non-radiative model behave in accord with the self-similar
picture, those of the other two models reproduce key aspects of the observed
X-ray properties: the core entropy, temperature-mass and luminosity-temperature
relations are all in good agreement with recent observations. This agreement
stems primarily from an increase in entropy with respect to the Non-radiative
clusters. Although the physics affecting the intra-cluster medium is very
different in the two models, the resulting cluster entropy profiles are very
similar.Comment: Accepted for publication in MNRAS. Minor changes following referee's
comment
Studies of x-ray clusters in cosmological simulations
Available from British Library Document Supply Centre- DSC:DXN057354 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo
A simulated τCDM cosmology cluster catalogue: the NFW profile and the temperature-mass scaling relations
We have extracted over 400 clusters, covering more than two decades in mass, from three simulations of the τCDM cosmology. This represents the largest uniform catalogue of simulated clusters ever produced. The clusters exhibit a wide variety of density profiles. Only a minority are well-fitted in their outer regions by the widely used density profile of Navarro, Frenk & White (NFW), which is applicable to relaxed haloes. Others have steeper outer density profiles, show sharp breaks in their density profiles, or have significant substructure. If we force a fit to the NFW profile, then the best-fitting concentrations decline with increasing mass, but this is driven primarily by an increase in substructure as one moves to higher masses. The temperature–mass relations for properties measured within a sphere enclosing a fixed overdensity all follow the self-similar form, T∝M2/3; however, the normalization is lower than the value inferred for observed clusters. The temperature–mass relations for properties measured within a fixed physical radius are significantly steeper then this. Both can be accurately predicted using the NFW model