176 research outputs found
Probing the dynamical state of galaxy clusters
We show how hydrostatic equilibrium in galaxy clusters can be quantitatively
probed combining X-ray, SZ, and gravitational-lensing data. Our previously
published method for recovering three-dimensional cluster gas distributions
avoids the assumption of hydrostatic equilibrium. Independent reconstructions
of cumulative total-mass profiles can then be obtained from the gas
distribution, assuming hydrostatic equilibrium, and from gravitational lensing,
neglecting it. Hydrostatic equilibrium can then be quantified comparing the
two. We describe this procedure in detail and show that it performs well on
progressively realistic synthetic data. An application to a cluster merger
demonstrates how hydrostatic equilibrium is violated and restored as the merger
proceeds.Comment: 10 pages, 6 figures, submitted to A&
How Baryonic Processes affect Strong Lensing properties of Simulated Galaxy Clusters
The observed abundance of giant arcs produced by galaxy cluster lenses and
the measured Einstein radii have presented a source of tension for LCDM.
Previous cosmological tests for high-redshift clusters (z>0.5) have suffered
from small number statistics in the simulated sample and the implementation of
baryonic physics is likely to affect the outcome. We analyse zoomed-in
simulations of a fairly large sample of cluster-sized objects, with Mvir >
3x10^14 Msun/h, identified at z=0.25 and z=0.5, for a concordance LCDM
cosmology. We start with dark matter only simulations, and then add gas
hydrodynamics, with different treatments of baryonic processes: non-radiative
cooling, radiative cooling with star formation and galactic winds powered by
supernova explosions, and finally including the effect of AGN feedback. We find
that the addition of gas in non-radiative simulations does not change the
strong lensing predictions significantly, but gas cooling and star formation
together significantly increase the number of expected giant arcs and the
Einstein radii, particularly for lower redshift clusters and lower source
redshifts. Further inclusion of AGN feedback reduces the predicted strong
lensing efficiencies such that the lensing probability distributions becomes
closer to those obtained for simulations including only dark matter. Our
results indicate that the inclusion of baryonic physics in simulations will not
solve the arc-statistics problem at low redshifts, when the physical processes
included provide a realistic description of cooling in the central regions of
galaxy clusters. [Abridged]Comment: 19 pages, 18 figures, 1 table, Accepted for publication in MNRA
Deconstructing Non-Abelian Gauge Theories at One Loop
Deconstruction of 5D Yang-Mills gauge theories is studied in next-to-leading
order accuracy. We calculate one-loop corrections to the mass spectrum of the
non-linear gauged sigma-model, which is the low energy effective theory of the
deconstructed theory. Renormalization is carried out following the standard
procedure of effective field theories. The relation between the radius of the
compactified fifth dimension and the symmetry breaking scale of the non-linear
sigma-model is modified by radiative corrections. We demonstrate that one can
match the low lying spectrum of the gauge boson masses of the effective 4D
gauged non-linear sigma-model to the Kaluza-Klein modes of the 5D theory at
one-loop accuracy
Cosmic degeneracies - I. Joint N-body simulations of modified gravity and massive neutrinos
We present the first suite of cosmological N-body simulations that simultaneously include the effects of two different and theoretically independent extensions of the standard Lambda cold dark matter (Lambda CDM) cosmological scenario - namely an f (R) theory of modified gravity and a cosmological background of massive neutrinos - with the aim to investigate their possible observational degeneracies. We focus on three basic statistics of the large-scale matter distribution, more specifically the non-linear matter power spectrum, the halo mass function, and the halo bias. Our results show that while these two extended models separately determine very prominent and potentially detectable features in all the three statistics, when we allow them to be simultaneously at work these features are strongly suppressed. In particular, when an f (R) gravity model with f(R0) = -1 x 10(-4) is combined with a total neutrino mass of Sigma(i)m(nu i) = 0.4 eV, the resulting matter power spectrum, halo mass function, and bias at z = 0 are found to be consistent with the standard model's predictions at the less than or similar to 10, less than or similar to 20, and less than or similar to 5 per cent accuracy levels, respectively. Therefore, our results imply an intrinsic theoretical limit to the effective discriminating power of present and future observational data sets with respect to these widely considered extensions of the standard cosmological scenario
The effect of stellar and AGN feedback on the low-redshift Lyman a forest in the Sherwood simulation suite
We study the effect of different feedback prescriptions on the properties of
the low redshift () Ly forest using a selection of
hydrodynamical simulations drawn from the Sherwood simulation suite. The
simulations incorporate stellar feedback, AGN feedback and a simplified scheme
for efficiently modelling the low column density Ly forest. We confirm
a discrepancy remains between Cosmic Origins Spectrograph (COS) observations of
the Ly forest column density distribution function (CDDF) at for high column density systems (), as
well as Ly velocity widths that are too narrow compared to the COS
data. Stellar or AGN feedback -- as currently implemented in our simulations --
have only a small effect on the CDDF and velocity width distribution. We
conclude that resolving the discrepancy between the COS data and simulations
requires an increase in the temperature of overdense gas with --,
either through additional He photo-heating at or
fine-tuned feedback that ejects overdense gas into the IGM at just the right
temperature for it to still contribute significantly to the Ly forest.
Alternatively a larger, currently unresolved turbulent component to the line
width could resolve the discrepancy
HIFLUGCS: Galaxy cluster scaling relations between X-ray luminosity, gas mass, cluster radius, and velocity dispersion
We present relations between X-ray luminosity and velocity dispersion
(L-sigma), X-ray luminosity and gas mass (L-Mgas), and cluster radius and
velocity dispersion (r500-sigma) for 62 galaxy clusters in the HIFLUGCS, an
X-ray flux-limited sample minimizing bias toward any cluster morphology. Our
analysis in total is based on ~1.3Ms of clean X-ray XMM-Newton data and 13439
cluster member galaxies with redshifts. Cool cores are among the major
contributors to the scatter in the L-sigma relation. When the
cool-core-corrected X-ray luminosity is used the intrinsic scatter decreases to
0.27 dex. Even after the X-ray luminosity is corrected for the cool core, the
scatter caused by the presence of cool cores dominates for the low-mass
systems. The scatter caused by the non-cool-core clusters does not strongly
depend on the mass range, and becomes dominant in the high-mass regime. The
observed L-sigma relation agrees with the self-similar prediction, matches that
of a simulated sample with AGN feedback disregarding six clusters with <45
cluster members with spectroscopic redshifts, and shows a common trend of
increasing scatter toward the low-mass end, i.e., systems with sigma<500km/s. A
comparison of observations with simulations indicates an AGN-feedback-driven
impact in the low-mass regime. The best fits to the relations
for the disturbed clusters and undisturbed clusters in the observational sample
closely match those of the simulated samples with and without AGN feedback,
respectively. This suggests that one main cause of the scatter is AGN activity
providing feedback in different phases, e.g., during a feedback cycle. The
slope and scatter in the observed r500-sigma relation is similar to that of the
simulated sample with AGN feedback except for a small offset but still within
the scatter.Comment: 45 pages, 28 figures, A&A proof-version, high-resolution figures in
Appendix F can be found in the electronic version on the A&A we
Arc sensitivity to cluster ellipticity, asymmetries and substructures
We investigate how ellipticity, asymmetries and substructures separately
affect the ability of galaxy clusters to produce strong lensing events, i.e.
gravitational arcs, and how they influence the arc morphologies and fluxes.
This is important for those studies aiming, for example, at constraining
cosmological parameters from statistical lensing, or at determining the inner
structure of galaxy clusters through gravitational arcs. We do so by creating
two-dimensional gradually smoothed, differently elliptical and asymmetric
versions of some numerical models. On average, we find that the contributions
of ellipticity, asymmetries and substructures amount to ~40%, ~10% and ~30% of
the total strong lensing cross section, respectively. However, our analysis
shows that substructures play a more important role in less elliptical and
asymmetric clusters, even if located at large distances from the cluster
centers (~1Mpc/h). Conversely, their effect is less important in highly
asymmetric lenses. The morphology, position and flux of individual arcs are
strongly affected by the presence of substructures in the clusters. Removing
substructures on spatial scales <~50kpc/h, roughly corresponding to mass scales
<~5 10^{10}M_\odot/h, alters the image multiplicity of ~35% of the sources used
in the simulations and causes position shifts larger than 5'' for ~40% of the
arcs longer than 5''. We conclude that any model for cluster lens cannot
neglect the effects of ellipticity, asymmetries and substructures. On the other
hand, the high sensitivity of gravitational arcs to deviations from regular,
smooth and symmetric mass distributions suggests that strong gravitational
lensing is potentially a powerfull tool to measure the level of substructures
and asymmetries in clusters.Comment: 16 pages, 18 figures. Accepted version. Version with full resolution
images can be found at
http://www.ita.uni-heidelberg.de/~massimo/sub/publications.htm
On the over-concentration problem of strong lensing clusters
Lambda cold dark matter paradigm predicts that galaxy clusters follow an
universal mass density profile and fit a well defined mass-concentration
relation, with lensing clusters being preferentially triaxial haloes elongated
along the line of sight. Oddly, recent strong and weak lensing analyses of
clusters with a large Einstein radius suggested those haloes to be highly
over-concentrated. Here, we investigate what intrinsic shape and orientation an
halo should have to account for both theoretical predictions and observations.
We considered a sample of 10 strong lensing clusters. We first measured their
elongation assuming a given mass-concentration relation. Then, for each cluster
we found the intrinsic shape and orientation which are compatible with the
inferred elongation and the measured projected ellipticity. We distinguished
two groups. The first one (nearly one half) seems to be composed of outliers of
the mass-concentration relation, which they would fit only if they were
characterised by a filamentary structure extremely elongated along the line of
sight, that is not plausible considering standard scenarios of structure
formations. The second sample supports expectations of N-body simulations which
prefer mildly triaxial lensing clusters with a strong orientation bias.Comment: 11 pages, 8 figures, in press on MNRA
Effects of the halo concentration distribution on strong-lensing optical depth and X-ray emission
We use simulated merger trees of galaxy-cluster halos to study the effect of
the halo concentration distribution on strong lensing and X-ray emission. Its
log-normal shape typically found in simulations favors outliers with high
concentration. Since, at fixed mass, more concentrated halos tend to be more
efficient lenses, the scatter in the concentration increases the strong-lensing
optical depth by . Within cluster samples, mass and concentration
have counteracting effects on strong lensing and X-ray emission because the
concentration decreases for increasing mass. Selecting clusters by
concentration thus has no effect on the lensing cross section. The most
efficiently lensing and hottest clusters are typically the \textit{least}
concentrated in samples with a broad mass range. Among cluster samples with a
narrow mass range, however, the most strongly lensing and X-ray brightest
clusters are typically 10% to 25% more concentrated.Comment: 12 pages, 10 figures. Version accepted by A&
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