151 research outputs found
Global cluster morphology and its evolution: X-ray data vs CDM, LCDM and mixed models
The global structure of galaxy clusters and its evolution are tested within a
large set of TREESPH simulations, so to allow a fair statistical comparison
with available X-ray data. Structure tests are based on the "power ratios",
introduced by Buote & Tsai. Cosmological models considered are CDM, LCDM
(Omega_L=0.7) and CHDM (1 mass.neu., Omega_h = 0.2). All models are normalized
to provide a fair number density of clusters. For each model we run a P3M
simulation in a large box, where we select the most massive 40 clusters. Going
back to the initial redshift we run a hydro-TREESPH simulation for each of
them. In this way we perform a statistical comparison of the global morphology
of clusters, for each cosmological model, with ROSAT data, using Student
t-test, F-test and K-S test. The last test and its generalization to 2--D
distributions are also used to compare the joint distributions of 2 or 3 power
ratios. We find that, using DM distribution, instead of gas, as done by some
authors, leads to biased results, as baryons are distributed in a less
structured way than DM. We also find that the cosmological models considered
have different behaviours in these tests: LCDM has the worst performance. CDM
and our CHDM have similar scores. The general trend of power ratio
distributions is already fit by these models, but a further improvement is
expected either from a different DM mix or a non-flat CDM model.Comment: 29 pages (LaTeX,macros included), 9 figure.ps & 3 tables included. To
appear on New Astronom
Mixed Dark Matter from Axino Distribution
We study the possibility of mixed dark matter obtained through the phase
space distribution of a single particle. An example is offered in the context
of SUSY models with a Peccei-Quinn symmetry. Axinos in the 100 keV range can
naturally have both thermal and non-thermal components. The latter one arises
from the lightest neutralino decays and derelativizes at z ~ 10^4.Comment: Figures added, references fixed. Version accepted for publication on
Phys. Rev. D. LaTeX. 9 pages, 3 figures, uses epsfig.st
Extending the Coyote emulator to dark energy models with standard - parametrization of the equation of state
We discuss an extension of the Coyote emulator to predict non-linear matter
power spectra of dark energy (DE) models with a scale factor dependent equation
of state of the form w = w_0 + ( 1 - a )w_a . The extension is based on the
mapping rule between non-linear spectra of DE models with constant equation of
state and those with time varying one originally introduced in ref. [40]. Using
a series of N-body simulations we show that the spectral equivalence is
accurate to sub-percent level across the same range of modes and redshift
covered by the Coyote suite. Thus, the extended emulator provides a very
efficient and accurate tool to predict non-linear power spectra for DE models
with w_0 - w_a parametrization. According to the same criteria we have
developed a numerical code, and we have implemented in a dedicated module for
the CAMB code, that can be used in combination with the Coyote Emulator in
likelihood analyses of non-linear matter power spectrum measurements. All codes
can be found at https://github.com/luciano-casarini/PKequalComment: All codes can be found at https://github.com/luciano-casarini/PKequa
Tracing the Nature of Dark Energy with Galaxy Distribution
Dynamical Dark Energy (DE) is a viable alternative to the cosmological
constant. Yet, constructing tests to discriminate between Lambda and dynamical
DE models is difficult because the differences are not large. In this paper we
explore tests based on the galaxy mass function, the void probability function
(VPF), and the number of galaxy clusters. At high z the number density of
clusters shows large differences between DE models, but geometrical factors
reduce the differences substantially. We find that detecting a model dependence
in the cluster redshift distribution is a hard challenge. We show that the
galaxy redshift distribution is potentially a more sensitive characteristics.
We do so by populating dark matter halos in Nbody simulations with galaxies
using well-tested Halo Occupation Distribution (HOD). We also estimate the Void
Probability Function and find that, in samples with the same angular surface
density of galaxies in different models, the VPF is almost model independent
and cannot be used as a test for DE. Once again, geometry and cosmic evolution
compensate each other. By comparing VPF's for samples with fixed galaxy mass
limits, we find measurable differences.Comment: 12 pages, 11 figures, dependence on mass-luminosity relation
discussed, minor changes to match the accepted version by MNRA
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