53 research outputs found
Constraining cosmological models with cluster power spectra
Using extensive N-body simulations we estimate redshift space power spectra
of clusters of galaxies for different cosmological models (SCDM, TCDM, CHDM,
Lambda-CDM, OCDM, BSI, tau-CDM) and compare the results with observational data
for Abell-ACO clusters. Our mock samples of galaxy clusters have the same
geometry and selection functions as the observational sample which contains 417
clusters of galaxies in a double cone of galactic latitude |b| > 30 degrees up
to a depth of 240 Mpc/h.
The power spectrum has been estimated for wave numbers k in the range 0.03 <
k k_max ~ 0.05 h/Mpc the power spectrum of the Abell-ACO
clusters has a power-law shape, P(k)\propto k^n, with n ~ -1.9, while it
changes sharply to a positive slope at k < k_max. By comparison with the mock
catalogues SCDM, TCDM (n=0.9), and also OCDM with Omega_0 = 0.35 are rejected.
Better agreement with observation can be found for the Lambda-CDM model with
Omega_0 = 0.35 and h = 0.7 and the CHDM model with two degenerate neutrinos and
Omega_HDM = 0.2 as well as for a CDM model with broken scale invariance (BSI)
and the tau-CDM model. As for the peak in the Abell-ACO cluster power spectrum,
we find that it does not represent a very unusual finding within the set of
mock samples extracted from our simulations.Comment: LaTeX, 27 pages, 8 figures (EPS). Revised version (title changed,
CHDM model added, discussion expanded). Accepted by New
Entropy of gas and dark matter in galaxy clusters
On the basis of a large scale 'adiabatic', namely non-radiative and
non-dissipative, cosmological smooth particle hydrodynamic simulation we
compare the entropy profiles of the gas and the dark matter (DM) in galaxy
clusters. The quantity K_g = T_g \rho_g^{-2/3} provides a measure for the
entropy of the intra-cluster gas. By analogy with the thermodynamic variables
of the gas the velocity dispersion of the DM is associated with a formal
temperature and thereby K_DM = \sigma_DM^2 \rho_DM^{-2/3} is defined. This DM
entropy is related to the DM phase space density by K_DM \propto Q_DM^{-2/3}.
In accord with other studies the DM phase space density follows a power law
behaviour, Q_DM \propto r^{-1.82}, which corresponds to K_DM \propto r^{1.21}.
The simulated intra-cluster gas has a flat entropy core within (0.8 \pm 0.4)
R_s, where R_s is the NFW scale radius. The outer profile follows the DM
behaviour, K_g \propto r^{1.21}, in close agreement with X-ray observations.
Upon scaling the DM and gas densities by their mean cosmological values we find
that outside the entropy core a constant ratio of K_g / K_{DM} = 0.71 \pm 0.18
prevails. By extending the definition of the gas temperature to include also
the bulk kinetic energy the ratio of the DM and gas extended entropy is found
to be unity for r > 0.8 R_s. The constant ratio of the gas thermal entropy to
that of the DM implies that observations of the intra-cluster gas can provide
an almost direct probe of the DM.Comment: 7 pages, 8 figures, accepted for publication in MNRAS, web page of
the The Marenostrum Numerical Cosmology Project :
http://astro.ft.uam.es/~marenostrum
Strong lensing in the MareNostrum Universe II: scaling relations and optical depths
The strong lensing events that are observed in compact clusters of galaxies
can, both statistically and individually, return important clues about the
structural properties of the most massive structures in the Universe.
Substantial work is ongoing in order to understand the degree of similarity
between the lensing cluster population and the population of clusters as a
whole, with members of the former being likely more massive, compact, and
substructured than members of the latter. In this work we exploit synthetic
clusters extracted from the {\sc MareNostrum Universe} cosmological simulation
in order to estimate the correlation between the strong lensing efficiency and
other bulk properties of lensing clusters, such as the virial mass and the
bolometric X-ray luminosity. We found that a positive correlation exist between
all these quantities, with the substantial scatter being smaller for the
luminosity-cross section relation. We additionally used the relation between
the lensing efficiency and the virial mass in order to construct a synthetic
optical depth that agrees well with the true one, while being extremely faster
to be evaluated. We finally estimated what fraction of the total giant arc
abundance is recovered when galaxy clusters are selected according to their
dynamical activity or their X-ray luminosity. Our results show that there is a
high probability for high-redshift strong lensing clusters to be substantially
far away from dynamical equilibrium, and that of the total amount of
giant arcs are lost if looking only at very X-ray luminous objects.Comment: 15 pages, 10 figures. Accepted by A&
Is AGN feedback necessary to form red elliptical galaxies?
We have used GADGET2 to simulate the formation of an elliptical galaxy in a
cosmological dark matter halo with mass 3x10^12M_Sun/h. Using a stellar
population synthesis model has allowed us to compute magnitudes, colours and
surface brightness profiles. We have included a model to follow the growth of a
central black hole and we have compared the results of simulations with and
without feedback from AGNs. We have studied the interplay between cold gas
accretion and merging in the development of galactic morphologies, the link
between colour and morphology evolution, the effect of AGN feedback on the
photometry of early type galaxies, the redshift evolution in the properties of
quasar hosts, and the impact of AGN winds on the chemical enrichment of the
intergalactic medium (IGM). We have found that the early phases of galaxy
formation are driven by the accretion of cold filamentary flows, which form a
disc at the centre of the dark matter halo. When the dark matter halo is
sufficiently massive to support the propagation of a stable shock, cold
accretion is shut down, and the star formation rate begins to decline. Mergers
transform the disc into an elliptical galaxy, but also bring gas into the
galaxy. Without a mechanism that removes gas from the merger remnants, the
galaxy ends up with blue colours, atypical for its elliptical morphology. AGN
feedback can solve this problem even with a fairly low heating efficiency. We
have also demonstrated that AGN winds are potentially important for the metal
enrichment of the IGM a high redshift.(abridged)Comment: 19 pages and 17 figures, accepted to MNRAS ID: MN-07-1954-MJ.R1 . For
high resolution images please check following link:
http://www.aip.de/People/AKhalatyan/COSMOLOGY/BHCOSMO
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