37 research outputs found
New Cosmology with Clusters of Galaxies
The review summarizes present and future applications of galaxy clusters to
cosmology with emphasis on nearby X-ray clusters. The discussion includes the
density of dark matter, the normalization of the matter power spectrum,
neutrino masses, and especially the equation of state of the dark energy, the
interaction between dark energy and ordinary matter, gravitational holography,
and the effects of extra-dimensions.Comment: 32 pages, 10 figures, invited review at the joint conference of the
Czech Astron. Society and the Astron. Gesell. To appear in Reviews in Modern
Astronomy 18 on "From Cosmolgical Structures to the Milky Way", ed. S. Roese
The ROSAT-ESO Flux-Limited X-Ray (REFLEX) Galaxy Cluster Survey VI: Constraints on the cosmic matter density from the KL power spectrum
The Karhunen-Lo\'{e}ve (KL) eigenvectors and eigenvalues of the sample
correlation matrix are used to analyse the spatial fluctuations of the REFLEX
clusters of galaxies. The method avoids the disturbing effects of correlated
power spectral densities which affects all previous cluster measurements on Gpc
scales. Comprehensive tests use a large set of independent REFLEX-like mock
cluster samples extracted from the Hubble Volume Simulation. It is found that
unbiased measurements on Gpc scales are possible with the REFLEX data. The
distribution of the KL eigenvalues are consistent with a Gaussian random field
on the 93.4% confidence level. Assuming spatially flat cold dark matter models,
the marginalization of the likelihood contours over different sample volumes,
fiducial cosmologies, mass/X-ray luminosity relations and baryon densities,
yields the 95.4% confidence interval for the matter density of
. The N-body simulations show that cosmic variance,
although difficult to estimate, is expected to increase the confidence
intervals by about 50%.Comment: 11 pages, 7 figures, accepted for publication in MNRA
Observational Constraints on General Relativistic Energy Conditions, Cosmic Matter Density and Dark Energy from X-Ray Clusters of Galaxies and Type-Ia Supernovae
New observational constraints on the cosmic matter density and an
effectively redshift-independent equation of state parameter of the dark
energy are obtained while simultaneously testing the strong and null energy
conditions of general relativity on macroscopic scales. The combination of
REFLEX X-ray cluster and type-Ia supernova data shows that for a flat Universe
the strong energy condition might presently be violated whereas the null energy
condition seems to be fulfilled. This provides another observational argument
for the present accelerated cosmic expansion and the absence of exotic physical
phenomena related to a broken null energy condition. The marginalization of the
likelihood distributions is performed in a manner to include a large fraction
of the recently discussed possible systematic errors involved in the
application of X-ray clusters as cosmological probes. This yields for a flat
Universe, and
( errors without cosmic variance). The scatter in the different
analyses indicates a quite robust result around , leaving little room
for the introduction of new energy components described by quintessence-like
models or phantom energy. The most natural interpretation of the data is a
positive cosmological constant with $w_x=-1 or something like it.Comment: 11 pages, 5 figures, Astron. Astrophys. (in press
VADER - A Satellite Mission Concept For High Precision Dark Energy Studies
We present a satellite mission concept to measure the dark energy equation of
state parameter w with percent-level precision. The Very Ambitious Dark Energy
Research satellite (VADER) is a multi-wavelength survey mission joining X-ray,
optical, and IR instruments for a simultaneous spectral coverage from 4microns
(0.3eV) to 10keV over a field of view (FoV) of 1 square degree. VADER combines
several clean methods for dark energy studies, the baryonic acoustic
oscillations in the galaxy and galaxy cluster power spectrum and weak lensing,
for a joint analysis over an unrivalled survey volume. The payload consists of
two XMM-like X-ray telescopes with an effective area of 2,800cm^2 at 1.5keV and
state-of-the-art wide field DEPFET pixel detectors (0.1-10keV) in a curved
focal plane configuration to extend the FoV. The X-ray telescopes are
complemented by a 1.5m optical/IR telescope with 8 instruments for simultaneous
coverage of the same FoV from 0.3 to 4 microns. The 8 dichroic-separated bands
(u,g,r,z,J,H,K,L) provide accurate photometric galaxy redshifts, whereas the
diffraction-limited resolution of the central z-band allows precise shape
measurements for cosmic shear analysis.
The 5 year VADER survey will cover a contiguous sky area of 3,500 square
degrees to a depth of z~2 and will yield accurate photometric redshifts and
multi-wavelength object parameters for about 175,000 galaxy clusters, one
billion galaxies, and 5 million AGN. VADER will not only provide unprecedented
constraints on the nature of dark energy, but will additionally extend and
trigger a multitude of cosmic evolution studies to very large (>10 Gyrs)
look-back times.Comment: 14 pages, 7 figures, accepted for publication in the SPIE conference
proceeding
Analysing Large Scale Structure: I. Weighted Scaling Indices and Constrained Randomisation
The method of constrained randomisation is applied to three-dimensional
simulated galaxy distributions. With this technique we generate for a given
data set surrogate data sets which have the same linear properties as the
original data whereas higher order or nonlinear correlations are not preserved.
The analysis of the original and surrogate data sets with measures, which are
sensitive to nonlinearities, yields information about the existence of
nonlinear correlations in the data. We demonstrate how to generate surrogate
data sets from a given point distribution, which have the same linear
properties (power spectrum) as well as the same density amplitude distribution.
We propose weighted scaling indices as a nonlinear statistical measure to
quantify local morphological elements in large scale structure. Using
surrogates is is shown that the data sets with the same 2-point correlation
functions have slightly different void probability functions and especially a
different set of weighted scaling indices. Thus a refined analysis of the large
scale structure becomes possible by calculating local scaling properties
whereby the method of constrained randomisation yields a vital tool for testing
the performance of statistical measures in terms of sensitivity to different
topological features and discriminative power.Comment: 10 pages, 5 figures, accepted for publication in MNRA
Cross Correlations of X-ray and Optically Selected Clusters With Near Infrared and Optical Galaxies
We compute the real-space cluster-galaxy cross-correlation xi_cg(r) using the
ROSAT-ESO Flux Limited X-ray (REFLEX) cluster survey, a group catalogue
constructed from the final version of the 2dFGRS, and galaxies extracted from
2MASS and APM surveys. This first detailed calculation of the cross-correlation
for X-ray clusters and groups, is consistent with previous works and shows that
xi_cg(r) can not be described by a single power law. We analyse the clustering
dependence on the cluster X-ray luminosity L_X and virial mass M_vir thresholds
as well as on the galaxy limiting magnitude. We also make a comparison of our
results with those obtained for the halo-mass cross-correlation function in a
LambdaCDM N-body simulation to infer the scale dependence of galaxy bias around
clusters. Our results indicate that the distribution of galaxies shows a
significant anti-bias at highly non-linear small cluster-centric distances
(b_cg(r) ~ 0.7), irrespective of the group/cluster virial mass or X-ray
luminosity and galaxy characteristics, which show that a generic process
controls the efficiency of galaxy formation and evolution in high density
regions. On larger scales b_cg(r) rises to a nearly constant value of order
unity, the transition occuring at approximately 2 Mpch^(-1) for 2dF groups and
5 Mpch^(-1) for REFLEX clusters.Comment: 9 pages, 6 figures. Minor changes, replaced to match version accepted
for publication in MNRA
Analysing large scale structure: II. Testing for primordial non-Gaussianity in CMB maps using surrogates
The identification of non-Gaussian signatures in cosmic microwave background
(CMB) temperature maps is one of the main cosmological challenges today. We
propose and investigate altenative methods to analyse CMB maps. Using the
technique of constrained randomisation we construct surrogate maps which mimic
both the power spectrum and the amplitude distribution of simulated CMB maps
containing non-Gaussian signals. Analysing the maps with weighted scaling
indices and Minkowski functionals yield in both cases statistically significant
identification of the primordial non-Gaussianities. We demonstrate that the
method is very robust with respect to noise. We also show that Minkowski
functionals are able to account for non-linearities at higher noise level when
applied in combination with surrogates than when only applied to noise added
CMB maps and phase randomised versions of them, which only reproduce the power
spectrum.Comment: 17 pages, 12 figures, MNRAS, accepted for publicatio
The merger history of clusters and its effect on the X-ray properties of the intracluster medium
We investigate the growth over time of 20 massive (> 3 keV) clusters in a
hydrodynamical simulation of the LambdaCDM cosmology with radiative cooling.
The clusters show a variety of formation histories: some accrete most of their
mass in major mergers; others more gradually. During major mergers the
long-term (temporally-smoothed) luminosity increases such that the cluster
moves approximately along the Lx-Tx relation; between times it slowly
decreases, tracking the drift of the Lx-Tx relation. We identify several
different kinds of short-term luminosity and temperature fluctuations
associated with major mergers including double-peaked mergers in which the
global intracluster medium merges first (Lx and Tx increase together) and then
the cluster cores merge (Lx increases and Tx decreases). At both luminosity
peaks, clusters tend to appear spherical and relaxed, which may lead to biases
in high-redshift, flux-limited samples. There is no simple relationship between
scatter in the Lx-Tx relation and either recent or overall merger activity or
cluster formation time. The scatter in the Lx-M and Tx-M relations is reduced
if properties are measured within R_500 rather than R_vir.Comment: Accepted for publication in MNRAS, major revision including greater
statistical analysis. 17 pages, 17 figure
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm