87 research outputs found
The effect of radiative cooling on scaling laws of X-ray groups and clusters
We have performed cosmological simulations in a ΛCDM cosmology with and without radiative cooling in order to study the effect of cooling on the cluster scaling laws. Our simulations consist of 4.1 million particles each of gas and dark matter within a box size of 100 h-1 Mpc, and the run with cooling is the largest of its kind to have been evolved to z = 0. Our cluster catalogs both consist of over 400 objects and are complete in mass down to ~1013 h-1 M☉. We contrast the emission-weighted temperature-mass (Tew-M) and bolometric luminosity-temperature (Lbol-Tew) relations for the simulations at z = 0. We find that radiative cooling increases the temperature of intracluster gas and decreases its total luminosity, in agreement with the results of Pearce et al. Furthermore, the temperature dependence of these effects flattens the slope of the Tew-M relation and steepens the slope of the Lbol-Tew relation. Inclusion of radiative cooling in the simulations is sufficient to reproduce the observed X-ray scaling relations without requiring excessive nongravitational energy injection
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
Simulations of AGN feedback in galaxy clusters and groups: impact on gas fractions and the Lx-T scaling relation
Recently, rapid observational and theoretical progress has established that
black holes (BHs) play a decisive role in the formation and evolution of
individual galaxies as well as galaxy groups and clusters. In particular, there
is compelling evidence that BHs vigorously interact with their surroundings in
the central regions of galaxy clusters, indicating that any realistic model of
cluster formation needs to account for these processes. This is also suggested
by the failure of previous generations of hydrodynamical simulations without BH
physics to simultaneously account for the paucity of strong cooling flows in
clusters, the slope and amplitude of the observed cluster scaling relations,
and the high-luminosity cut-off of central cluster galaxies. Here we use
high-resolution cosmological simulations of a large cluster and group sample to
study how BHs affect their host systems. We focus on two specific properties,
the halo gas fraction and the X-ray luminosity-temperature scaling relation,
both of which are notoriously difficult to reproduce in self-consistent
hydrodynamical simulations. We show that BH feedback can solve both of these
issues, bringing them in excellent agreement with observations, without
alluding to the `cooling only' solution that produces unphysically bright
central galaxies. By comparing a large sample of simulated AGN-heated clusters
with observations, our new simulation technique should make it possible to
reliably calibrate observational biases in cluster surveys, thereby enabling
various high-precision cosmological studies of the dark matter and dark energy
content of the universe.Comment: 4 pages, 2 figures, minor revisions, ApJL in pres
Simulating the Hot X-ray Emitting Gas in Elliptical Galaxies
We study the chemo-dynamical evolution of elliptical galaxies and their hot
X-ray emitting gas using high-resolution cosmological simulations. Our Tree
N-body/SPH code includes a self-consistent treatment of radiative cooling, star
formation, supernovae feedback, and chemical enrichment. We present a series of
LCDM cosmological simulations which trace the spatial and temporal evolution of
heavy element abundance patterns in both the stellar and gas components of
galaxies. X-ray spectra of the hot gas are constructed via the use of the
vmekal plasma model, and analysed using XSPEC with the XMM EPN response
function. Simulation end-products are quantitatively compared with the
observational data in both the X-ray and optical regime. We find that radiative
cooling is important to interpret the observed X-ray luminosity, temperature,
and metallicity of the interstellar medium of elliptical galaxies. However,
this cooled gas also leads to excessive star formation at low redshift, and
therefore results in underlying galactic stellar populations which are too blue
with respect to observations.Comment: 6 pages, 3 figures, to appear in the proceedings of "The IGM/Galaxy
Connection - The Distribution of Baryons at z=0", ed. M. Putman & J.
Rosenberg; High resolution version is available at
http://astronomy.swin.edu.au/staff/dkawata/research/papers.htm
Cluster scaling relations from cosmological hydrodynamic simulations in dark energy dominated universe
Clusters are potentially powerful tools for cosmology provided their observed
properties such as the Sunyaev-Zel'dovich (SZ) or X-ray signals can be
translated into physical quantities like mass and temperature. Scaling
relations are the appropriate mean to perform this translation. It is
therefore, important to understand their evolution and their modifications with
respect to the physics and to the underlying cosmology. In this spirit, we
investigate the effect of dark energy on the X-ray and SZ scaling relations.
The study is based on the first hydro-simulations of cluster formation for
diferent models of dark energy. We present results for four dark energy models
which differ from each other by their equations of state parameter, .
Namely, we use a cosmological constant model (as a reference), a perfect
fluid with constant equation of state parameter and one with and a scalar field model (or quintessence) with varying . We generate
N-body/hydrodynamic simulations that include radiative cooling with the public
version of the Hydra code, modified to consider an arbitrary dark energy
component. We produce cluster catalogues for the four models and derive the
associated X-ray and SZ scaling relations. We find that dark energy has little
effect on scaling laws making it safe to use the CDM scalings for
conversion of observed quantities into temperature and masses.Comment: 9 pages, 7 figures, submitted to A&
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
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
Entropy scaling in galaxy clusters: insights from an XMM-Newton observation of the poor cluster A1983
An XMM-Newton observation of the cool (kT=2.1 keV) cluster A1983, at z=0.044,
is presented. Gas density and temperature profiles are calculated for the inner
500 h_{50}^{-1} kpc (~0.35 r_200). The outer regions of the surface brightness
profile are well described with a beta model with beta=0.74, but the central
regions require the introduction of a second component. The temperature profile
is flat at the exterior with a slight dip towards the centre. The total mass
profile, calculated assuming hydrostatic equilibrium, is consistent with an NFW
profile, but with a low concentration parameter c=3.75 +/- 0.74. The M/L_B
ratio profile shows that, at large scale, light traces mass to a reasonable
extent, and the M/L_B ratio at 0.35 r_200 is consistent with the trends with
mass observed in the optical. The M_Fe/L_B ratio is about two times less than
that observed for a cluster at 5 keV. The gas mass fraction rises rapidly to
level off at ~200 kpc; the value at 0.35 r_200 is ~8%. The scaling properties
of the emission measure profile are consistent with the empirical relation
\mgas \propto \Tx^{1.94}, and not with the self-similar relation \mgas \propto
\Tx^{1.5}. Comparison of the entropy profile of A1983 with that of the hot
cluster A1413 shows that the profiles are well scaled using the empirically
determined relation S \propto \Tx^{0.65}, suggesting that the slope of the S-T
relation is shallower than in the self-similar model. The form of the entropy
profiles is remarkably similar, and there is no sign of a larger isentropic
core in the cooler cluster. These data provide powerful agruments against
preheating models. In turn, there is now increasing observational support for a
trend of f_gas with system mass, which may go some way towards explaining the
observed scaling behaviour. (Abridged.)Comment: Final refereed version to appear in A&A; Figs 2, 7, 11 and 12 are low
re
Baryon fractions in clusters of galaxies: evidence against a preheating model for entropy generation
The Millennium Gas project aims to undertake smoothed-particle hydrodynamic
resimulations of the Millennium Simulation, providing many hundred massive
galaxy clusters for comparison with X-ray surveys (170 clusters with kTsl > 3
keV). This paper looks at the hot gas and stellar fractions of clusters in
simulations with different physical heating mechanisms. These fail to reproduce
cool-core systems but are successful in matching the hot gas profiles of
non-cool-core clusters. Although there is immense scatter in the observational
data, the simulated clusters broadly match the integrated gas fractions within
r500 . In line with previous work, however, they fare much less well when
compared to the stellar fractions, having a dependence on cluster mass that is
much weaker than is observed. The evolution with redshift of the hot gas
fraction is much larger in the simulation with early preheating than in one
with continual feedback; observations favour the latter model. The strong
dependence of hot gas fraction on cluster physics limits its use as a probe of
cosmological parameters.Comment: 16 pages, 18 figures, 4 tables. Accepted for publication in MNRA
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