1,046 research outputs found
The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX II) IV. X-ray Luminosity Function and First Constraints on Cosmological Parameters
The X-ray luminosity function is an important statistic of the census of
galaxy clusters and an important means to probe the cosmological model of our
Universe. Based on our recently completed REFLEX II cluster sample we construct
the X-ray luminosity function of galaxy clusters for several redshift slices
from to and discuss its implications. We find no significant
signature of redshift evolution of the luminosity function in the redshift
interval. We provide the results of fits of a parameterized Schechter function
and extensions of it which provide a reasonable characterization of the data.
Using a model for structure formation and galaxy cluster evolution we compare
the observed X-ray luminosity function with predictions for different
cosmological models. For the most interesting constraints for the cosmological
parameters and we obatain
and based on the statistical uncertainty alone.
Marginalizing over the most important uncertainties, the normalisation and
slope of the scaling relation, we find
and ( confidence limits). We compare our
results with those of the SZ-cluster survey provided by the PLANCK mission and
we find very good agreement with the results using PLANCK clusters as
cosmological probes, but we have some tension with PLANCK cosmological results
from the microwave background anisotropies. We also make a comparison with
other cluster surveys. We find good agreement with these previous results and
show that the REFLEX II survey provides a significant reduction in the
uncertainties compared to earlier measurements.Comment: Submitted for publication to Astronomy and Astrophysics, 15 pages, 17
figure
Abell 3627: A Nearby, X-ray Bright, and Massive Galaxy Cluster
The cluster A3627 was recently recognized to be a very massive, nearby
cluster in a galaxy survey close to the galactic plane. We are reporting on
ROSAT PSPC observations of this object which confirm that the cluster is indeed
very massive. The X-ray emission detected from the cluster extends over almost
1 degree in radius. The X-ray image is not spherically symmetric and shows
indications of an ongoing cluster merger. Due to the strong interstellar
absorption the spectral analysis and the gas temperature determination are
difficult. The data are consistent with an overall gas temperature in the range
5 to 10 keV. There are signs of temperature variations in the merger region. A
mass estimate based on the X-ray data yields values of \msu \ if extrapolated to the virial radius of Mpc. In
the ROSAT energy band (0.1 - 2.4 keV) the cluster emission yields a flux of
about erg s cm which makes A3627 the 6
brightest cluster in the ROSAT All Sky Survey. The cluster was missed in
earlier X-ray surveys because it was confused with a neighbouring X-ray bright,
galactic X-ray binary (1H1556-605). The large X-ray flux makes A3627 an
important target for future studies.Comment: 14 pages, Latex file, including aaspp.sty, 9 postscript figures and 1
table, accepted for publication by the Astrophysical Journa
The REFLEX Galaxy Cluster Survey VII: Omega_m and sigma_8 from cluster abundance and large-scale clustering
For the first time the large-scale clustering and the mean abundance of
galaxy clusters are analysed simultaneously to get precise constraints on the
normalized cosmic matter density and the linear theory RMS
fluctuations in mass . A self-consistent likelihood analysis is
described which combines, in a natural and optimal manner, a battery of
sensitive cosmological tests where observational data are represented by the
(Karhunen-Lo\'{e}ve) eigenvectors of the sample correlation matrix. This method
breaks the degeneracy between and . The cosmological tests
are performed with the ROSAT ESO Flux-Limited X-ray (REFLEX) cluster sample.
The computations assume cosmologically flat geometries and a non-evolving
cluster population mainly over the redshift range . The REFLEX sample
gives the cosmological constraints and their random errors of
and . Possible systematic errors are evaluated by estimating the
effects of uncertainties in the value of the Hubble constant, the baryon
density, the spectral slope of the initial scalar fluctuations, the mass/X-ray
luminosity relation and its intrinsic scatter, the biasing scheme, and the
cluster mass density profile. All these contributions sum up to total
systematic errors of and
.Comment: 10 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Central galaxy growth and feedback in the most massive nearby cool core cluster
We present multi-wavelength observations of the centre of RXCJ1504.1-0248 -
the galaxy cluster with the most luminous and relatively nearby cool core at
z~0.2. Although there are several galaxies within 100 kpc of the cluster core,
only the brightest cluster galaxy (BCG), which lies at the peak of the X-ray
emission, has blue colours and strong line-emission. Approximately 80 Msun/yr
of intracluster gas is cooling below X-ray emitting temperatures, similar to
the observed UV star formation rate of ~140 Msun/yr. Most star formation occurs
in the core of the BCG and in a 42 kpc long filament of blue continuum, line
emission, and X-ray emission, that extends southwest of the galaxy. The
surrounding filamentary nebula is the most luminous around any observed BCG.
The number of ionizing stars in the BCG is barely sufficient to ionize and heat
the nebula, and the line ratios indicate an additional heat source is needed.
This heat source can contribute to the H\alpha-deduced star formation rates
(SFRs) in BCGs and therefore the derived SFRs should only be considered upper
limits. AGN feedback can slow down the cooling flow to the observed mass
deposition rate if the black hole accretion rate is of the order of 0.5 Msun/yr
at 10% energy output efficiency. The average turbulent velocity of the nebula
is vturb ~325 km/s which, if shared by the hot gas, limits the ratio of
turbulent to thermal energy of the intracluster medium to less than 6%.Comment: 15 pages, 11 figures, MNRAS in press. Corrected typo in abstract
The X-ray Luminosity - Velocity Dispersion relation in the REFLEX Cluster Survey
We present an estimate of the bolometric X-ray luminosity - velocity
dispersion L_x - sigma_v relation measured from a new, large and homogeneous
sample of 171 low redshift, X-ray selected galaxy clusters. The linear fitting
of log(L_x) - log(sigma_v) gives L_x = 10^{32.72 \pm 0.08} sigma^{4.1 \pm
0.3}_v erg s^{-1} h^{-2}_{50}. Furthermore, a study of 54 clusters, for which
the X-ray temperature of the intracluster medium T is available, allows us to
explore two other scaling relations, L_x -T and sigma_v -T. From this sample we
obtain L_x \propto T^{3.1 \pm 0.2} and sigma_v \propto T^{1.00 \pm 0.16}, which
are fully consistent with the above result for the L_x-sigma_v. The slopes of
L_x -T and sigma_v -T are incompatible with the values predicted by
self-similarity (L_x \propto T^{2} \propto \sigma_v^4), thus suggesting the
presence of non-gravitational energy sources heating up the intracluster
medium, in addition to the gravitational collapse, in the early stages of
cluster formation. On the other hand, the result on log(L_x) - log(sigma_v)
supports the self-similar model.Comment: 9 pages, accepted for publication in MNRA
Who bears the burden of greening electricity?
Faced with the threat of climate change many countries are promoting renewable energies to decarbonize their energy system. A common policy to foster electricity from renewable energy sources are feed-in tariffs which are financed by surcharges on electricity prices. Higher electricity prices in turn raise concerns on regressive distributional impacts. In this paper, we investigate the distributional impacts of three alternative policies to subsidize renewable energy production in Spain: (i) exemptions from the electricity surcharge for residential consumers, (ii) an increase in mineral oil taxes, and (iii) an increase in value-added taxes. We find that all three options can attenuate the regressive distributional effects compared to feed-in tariffs. For our quantitative impact assessment, we couple a microsimulation model with a computable general equilibrium model to capture the incidence on heterogeneous households in an economy-wide framework.This research is supported by the Basque Government through the BERC 2018-2021 program and by the Spanish Ministry of Economy and Competitiveness MINECO through BC3 MarĂa de Maeztu excellence accreditation MDM-2017-0714. In addition, this study received funding from the Ministry of Science, Innovation and Universities of Spain ( RTI2018-093352-B-I00 ) and from the European Unio
The XMM/2dF survey III: Comparison between optical and X-ray cluster detection methods
We directly compare X-ray and optical techniques of cluster detection by
combining SDSS photometric data with a wide-field ( deg)
XMM-{\em Newton} survey in the North Galactic Pole region. The optical cluster
detection procedure is based on merging two independent selection methods - a
smoothing+percolation technique, and a Matched Filter Algorithm. The X-ray
cluster detection is based on a wavelet-based algorithm, incorporated in the
SAS v.5.2 package. The final optical sample counts 9 candidate clusters with
richness of more than 20 galaxies, corresponding roughly to APM richness class.
Three, of our optically detected clusters are also detected in our X-ray
survey. The most probable cause of the small number of optical cluster
candidates detected in our X-ray survey is that they are relatively poor
clusters, fainter than the X-ray flux limit (for extended sources) of our
survey .Comment: 9 pages, 5 figures, MNRAS accepte
Observational Constraints on General Relativistic Energy Conditions, Cosmic Matter Density and Dark Energy from X-Ray Clusters of Galaxies and Type-la Supernovae
New observational constraints on the cosmic matter density Ωm and an effectively redshift-independent equation
of state parameter wx 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, Ωm = 0.29+0.08 and wx = â0.95+0.30 (1Ï errors without â0.12 â0.35
cosmic variance). The scatter in the different analyses indicates a quite robust result around wx = â1, 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 wx = â1 or something like it
Spatially-resolved X-ray spectroscopy of the core of the Centaurus cluster
We present Chandra data from a 31.7 ks observation of the Centaurus cluster,
using the ACIS-S detector. Images of the X-ray emission show a plume-like
feature at the centre of the cluster, of extent 60 arcsec (20 kpc in
projection). The feature has the same metallicity as gas at a similar radius,
but is cooler. Using adaptive binning, we generate temperature, abundance and
absorption maps of the cluster core. The radial abundance profile shows that
the previously known, steep abundance gradient peaks with a metallicity of
1.3-1.8 Zsolar at a radius of about 45 arcsec (15 kpc), before falling back to
0.4 Zsolar at the centre of the cluster. A radial temperature profile shows
that the temperature decreases inwards. We determine the spatial distributions
of each of two temperature components, where applicable. The radiative cooling
time of the cooler component within the inner 10 arcsec (3 kpc) is less than
2x10^7 yr. X-ray holes in the image coincident with the radio lobes are seen,
as well as two outer sharp temperature drops, or cold fronts. The origin of the
plume is unclear. The existence of the strong abundance gradient is a strong
constraint on extensive convection or gas motion driven by a central radio
source.Comment: 11 pages, 14 figures (3 colour), accepted by MNRAS, high res. version
at http://www-xray.ast.cam.ac.uk/papers/cen1_accptd.pdf . Updated version
includes a section considering a non-thermal componen
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