1,673 research outputs found
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&
Comparison of an X-ray selected sample of massive lensing clusters with the MareNostrum Universe LCDM simulation
A long-standing problem of strong lensing by galaxy clusters regards the
observed high rate of giant gravitational arcs as compared to the predictions
in the framework of the "standard" cosmological model. Recently, few other
inconsistencies between theoretical expectations and observations have been
claimed which regard the large size of the Einstein rings and the high
concentrations of few clusters with strong lensing features. All of these
problems consistently indicate that observed galaxy clusters may be
gravitational lenses stronger than expected. We use clusters extracted from the
MareNostrum Universe to build up mock catalogs of galaxy clusters selected
through their X-ray flux. We use these objects to estimate the probability
distributions of lensing cross sections, Einstein rings, and concentrations for
the sample of 12 MACS clusters at presented in Ebeling et al. (2007)
and discussed in Zitrin et al. (2010). We find that simulated clusters produce
less arcs than observed clusters do. The medians of the
distributions of the Einstein ring sizes differ by between
simulations and observations. We estimate that, due to cluster triaxiality and
orientation biases affecting the lenses with the largest cross sections, the
concentrations of the individual MACS clusters inferred from the lensing
analysis should be up to a factor of larger than expected from the
CDM model. The arc statistics, the Einstein ring, and the
concentration problems in strong lensing clusters are mitigated but not solved
on the basis of our analysis. Nevertheless, due to the lack of redshifts for
most of the multiple image systems used for modeling the MACS clusters, the
results of this work will need to be verified with additional data. The
upcoming CLASH program will provide an ideal sample for extending our
comparison (abridged).Comment: 11 pages, 9 figures, accepted for publication on A&
Strong lensing in the MareNostrum Universe: biases in the cluster lens population
Strong lensing is one of the most direct probes of the mass distribution in
the inner regions of galaxy clusters. It can be used to constrain the density
profiles and to measure the mass of the lenses. Moreover, the abundance of
strong lensing events can be used to constrain the structure formation and the
cosmological parameters through the so-called "arc-statistics" approach.
However, several issues related to the usage of strong lensing clusters in
cosmological applications are still controversial, leading to the suspect that
several biases may affect this very peculiar class of objects. With this study
we aim at better understanding the properties of galaxy clusters which can
potentially act as strong lenses. We do so by investigating the properties of a
large sample of galaxy clusters extracted from the N-body/hydrodynamical
simulation MareNostrum Universe. We explore the correlation between the cross
section for lensing and many properties of clusters, like the mass, the
three-dimensional and projected shapes, their concentrations, the X-ray
luminosity and the dynamical activity. We find that the probability of strong
alignments between the major axes of the lenses and the line of sight is a
growing function of the lensing cross section. In projection, the strong lenses
appear rounder within R200, but we find that their cores tend to be more
elliptical as the lensing cross section increases. We also find that the
cluster concentrations estimated from the projected density profiles tend to be
biased high. The X-ray luminosity of strong lensing clusters is higher than
that of normal lenses of similar mass and redshift. This is particular
significant for the least massive lenses. Finally, we find that the strongest
lenses generally exhibit an excess of kinetic energy within the virial radius,
indicating that they are more dynamically active than usual clusters.Comment: 22 pages, 18 figures, accepted for publication on A&
The Dark UNiverse Explorer (DUNE): Proposal to ESA's Cosmic Vision
The Dark UNiverse Explorer (DUNE) is a wide-field space imager whose primary
goal is the study of dark energy and dark matter with unprecedented precision.
For this purpose, DUNE is optimised for the measurement of weak gravitational
lensing but will also provide complementary measurements of baryonic accoustic
oscillations, cluster counts and the Integrated Sachs Wolfe effect. Immediate
auxiliary goals concern the evolution of galaxies, to be studied with
unequalled statistical power, the detailed structure of the Milky Way and
nearby galaxies, and the demographics of Earth-mass planets. DUNE is an
Medium-class mission which makes use of readily available components, heritage
from other missions, and synergy with ground based facilities to minimise cost
and risks. The payload consists of a 1.2m telescope with a combined visible/NIR
field-of-view of 1 deg^2. DUNE will carry out an all-sky survey, ranging from
550 to 1600nm, in one visible and three NIR bands which will form a unique
legacy for astronomy. DUNE will yield major advances in a broad range of fields
in astrophysics including fundamental cosmology, galaxy evolution, and
extrasolar planet search. DUNE was recently selected by ESA as one of the
mission concepts to be studied in its Cosmic Vision programme.Comment: Accepted in Experimental Astronom
Mass profiles and concentration-dark matter relation in X-ray luminous galaxy clusters
(Abriged) Assuming that the hydrostatic equilibrium holds between the
intracluster medium and the gravitational potential, we constrain the NFW
profiles in a sample of 44 X-ray luminous galaxy clusters observed with
XMM-Newton in the redshift range 0.1-0.3. We evaluate several systematic
uncertainties that affect our reconstruction of the X-ray masses. We measure
the concentration c200, the dark mass M200 and the gas mass fraction within
R500 in all the objects of our sample, providing the largest dataset of mass
parameters for galaxy clusters in this redshift range. We confirm that a tight
correlation between c200 and M200 is present and in good agreement with the
predictions from numerical simulations and previous observations. When we
consider a subsample of relaxed clusters that host a Low-Entropy-Core (LEC), we
measure a flatter c-M relation with a total scatter that is lower by 40 per
cent. From the distribution of the estimates of c200 and M200, with associated
statistical (15-25%) and systematic (5-15%) errors, we use the predicted values
from semi-analytic prescriptions calibrated through N-body numerical runs and
measure sigma_8*Omega_m^(0.60+-0.03)= 0.45+-0.01 (at 2 sigma level, statistical
only) for the subsample of the clusters where the mass reconstruction has been
obtained more robustly, and sigma_8*Omega_m^(0.56+-0.04) = 0.39+-0.02 for the
subsample of the 11 more relaxed LEC objects. With the further constraint from
the fgas distribution in our sample, we break the degeneracy in the
sigma_8-Omega_m plane and obtain the best-fit values sigma_8~1.0+-0.2
(0.75+-0.18 when the subsample of the more relaxed objects is considered) and
Omega_m = 0.26+-0.01.Comment: 21 pages. A&A in press. Minor revisions to match accepted version.
Corrected 2nd and 3rd column in Table 3, and equation (A.4
Weighing simulated galaxy clusters using lensing and X-ray
We aim at investigating potential biases in lensing and X-ray methods to
measure the cluster mass profiles. We do so by performing realistic simulations
of lensing and X-ray observations that are subsequently analyzed using
observational techniques. The resulting mass estimates are compared among them
and with the input models. Three clusters obtained from state-of-the-art
hydrodynamical simulations, each of which has been projected along three
independent lines-of-sight, are used for this analysis. We find that strong
lensing models can be trusted over a limited region around the cluster core.
Extrapolating the strong lensing mass models to outside the Einstein ring can
lead to significant biases in the mass estimates, if the BCG is not modeled
properly for example. Weak lensing mass measurements can be largely affected by
substructures, depending on the method implemented to convert the shear into a
mass estimate. Using non-parametric methods which combine weak and strong
lensing data, the projected masses within R200 can be constrained with a
precision of ~10%. De-projection of lensing masses increases the scatter around
the true masses by more than a factor of two due to cluster triaxiality. X-ray
mass measurements have much smaller scatter (about a factor of two smaller than
the lensing masses) but they are generally biased low by 5-20%. This bias is
ascribable to bulk motions in the gas of our simulated clusters. Using the
lensing and the X-ray masses as proxies for the true and the hydrostatic
equilibrium masses of the simulated clusters and averaging over the cluster
sample we are able to measure the lack of hydrostatic equilibrium in the
systems we have investigated.Comment: 27 pages, 21 figures, accepted for publication on A&A. Version with
full resolution images can be found at
http://pico.bo.astro.it/~massimo/Public/Papers/massComp.pd
Is the Number of Giant Arcs in LCDM Consistent With Observations?
We use high-resolution N-body simulations to study the galaxy-cluster
cross-sections and the abundance of giant arcs in the CDM model.
Clusters are selected from the simulations using the friends-of-friends method,
and their cross-sections for forming giant arcs are analyzed. The background
sources are assumed to follow a uniform ellipticity distribution from 0 to 0.5
and to have an area identical to a circular source with diameter 1\arcsec. We
find that the optical depth scales as the source redshift approximately as
\tau_{1''} = 2.25 \times 10^{-6}/[1+(\zs/3.14)^{-3.42}] (0.6<\zs<7). The
amplitude is about 50% higher for an effective source diameter of 0.5\arcsec.
The optimal lens redshift for giant arcs with the length-to-width ratio ()
larger than 10 increases from 0.3 for \zs=1, to 0.5 for \zs=2, and to
0.7-0.8 for \zs>3. The optical depth is sensitive to the source redshift, in
qualitative agreement with Wambsganss et al. (2004). However, our overall
optical depth appears to be only 10% to 70% of those from previous
studies. The differences can be mostly explained by different power spectrum
normalizations () used and different ways of determining the
ratio. Finite source size and ellipticity have modest effects on the optical
depth. We also found that the number of highly magnified (with magnification
) and ``undistorted'' images (with ) is comparable to the
number of giant arcs with and . We conclude that our
predicted rate of giant arcs may be lower than the observed rate, although the
precise `discrepancy' is still unclear due to uncertainties both in theory and
observations.Comment: Revised version after the referee's reports (32 pages,13figures). The
paper has been significantly revised with many additions. The new version
includes more detailed comparisons with previous studies, including the
effects of source size and ellipticity. New discussions about the redshift
distribution of lensing clusters and the width of giant arcs have been adde
Does repetitive thinking mediate the relationship between self-compassion and competition anxiety in athletes?
Due to the promising effect of self-compassion interventions in sports, it was the main goal of this study to investigate, if two aspects of repetitive thinking, worry and rumination, mediate the possible relation of self-compassion on competition anxiety of women and men in different types of sport (team- vs. individual sport). Two hundred and ninety-three athletes participated, 127 were soccer players, 103 handball players, and 63 athletes practiced an individual sport. They completed four questionnaires of sport competition anxiety, rumination, worry, and self-compassion. The results showed that for both rumination and worry, women had higher values than men and individual athletes had higher values than athletes from team sport. Women had higher values in the negative scale of self-compassion compared to men, and individual athletes and handball players had lower values than soccer players. The result of a mediation analysis demonstrated that the relation between the negative scale of self-compassion and the somatic anxiety and concern aspect of competition anxiety was mediated by worry
The on-demand warehousing problem
Warehouses are key elements of supply chain networks, and great attention is paid to increase their efficiency. Highly volatile space requirements are enablers of innovative resource sharing concepts, where warehouse capacities are traded on online platforms. In this context, our paper introduces the on-demand warehousing problem from the perspective of platform providers. The objective prioritises demand–supply matching with maximisation of the number of transactions. If there is a tie, the secondary objective maximises the number of suppliers matched with at least one customer and the number of customers that have matches within a specific threshold with respect to the minimum achievable cost. Besides the mathematical integer programming formulation, a myopic list-based heuristic and an efficient matheuristic approach are presented and benchmarked against the performance of a commercial optimisation solver. The impact of several parameters on the platform's objective is analysed. A particularly relevant finding is that the pricing flexibility on the demand side does not necessarily imply higher payments to the supply side. All data instances are made available publicly to encourage more researchers to work on this timely and challenging topic
A comunicação da Embrapa Trigo em um dia de campo de inverno 2013.
Editores técnicos: Joseani Mesquita Antunes, Ana Lídia Variani Bonato, Márcia Barrocas Moreira Pimentel
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