1,040 research outputs found
High redshift X-ray galaxy clusters. II. The L_X-T relationship revisited
In this paper we re-visit the observational relation between X-ray luminosity
and temperature for high-z galaxy clusters and compare it with the local L_X-T
and with theoretical models. To these ends we use a sample of 17 clusters
extracted from the Chandra archive supplemented with additional clusters from
the literature, either observed by Chandra or XMM-Newton, to form a final
sample of 39 high redshift (0.25 < z < 1.3) objects. Different statistical
approaches are adopted to analyze the L_X-T relation. The slope of the L_X-T
relation of high redshift clusters is steeper than expected from the
self-similar model predictions and steeper, even though still compatible within
the errors, than the local L_X-T slope. The distant cluster L_X-T relation
shows a significant evolution with respect to the local Universe: high-z
clusters are more luminous than the local ones by a factor ~2 at any given
temperature. The evolution with redshift of the L_X-T relation cannot be
described by a single power law nor by the evolution predicted by the
self-similar model. We find a strong evolution, similar or stronger than the
self-similar model, from z = 0 to z <0.3 followed by a much weaker, if any,
evolution at higher redshift. The weaker evolution is compatible with
non-gravitational models of structure formation. According to us a
statistically significant sample of nearby clusters (z < 0.25) should be
observed with the current available X-ray telescopes to completely exclude
observational effects due to different generation detectors and to understand
this novel result.Comment: 14 pages, 10 postscript figures. Accepted for publication in
Astronomy & Astrophysics. Corrected typo
The X-ray Size-Temperature Relation for Intermediate Redshift Galaxy Clusters
We present the first measurements of the X-ray size-temperature (ST) relation
in intermediate redshift (z~0.30) galaxy clusters. We interpret the local ST
relation (z~0.06) in terms of underlying scaling relations in the cluster dark
matter properties, and then we use standard models for the redshift evolution
of those dark matter properties to show that the ST relation does not evolve
with redshift. We then use ROSAT HRI observations of 11 clusters to examine the
intermediate redshift ST relation; for currently favored cosmological
parameters, the intermediate redshift ST relation is consistent with that of
local clusters. Finally, we use the ST relation and our evolution model to
measure angular diameter distances; with these 11 distances we evaluate
constraints on Omega_M and Omega_L which are consistent with those derived from
studies of Type Ia supernovae. The data rule out a model with Omega_M=1 and
Omega_L=0 with 2.5 sigma confidence. When limited to models where
Omega_M+Omega_L=1, these data are inconsistent with Omega_M=1 with 3 sigma
confidence.Comment: ApJ: submitted April 7, accepted June 28, to appear Dec 1 (vol 544
Quantum many-body scars from unstable periodic orbits
Unstable periodic orbits (UPOs) play a key role in the theory of chaos,
constituting the "skeleton" of classical chaotic systems and "scarring" the
eigenstates of the corresponding quantum system. Recently, nonthermal many-body
eigenstates embedded in an otherwise thermal spectrum have been identified as a
many-body generalization of quantum scars. The latter, however, are not clearly
associated to a chaotic phase space, and the connection between the single- and
many-body notions of quantum scars remains therefore incomplete. Here, we find
the first quantum many-body scars originating from UPOs of a chaotic phase
space. Remarkably, these states verify the eigenstate thermalization
hypothesis, and we thus refer to them as thermal quantum many-body scars. While
they do not preclude thermalization, their spectral structure featuring
approximately equispaced towers of states yields an anomalous oscillatory
dynamics preceding thermalization for wavepackets initialized on an UPO.
Remarkably, our model hosts both types of scars, thermal and nonthermal, and
allows to study the crossover between the two. Our work illustrates the
fundamental principle of classical-quantum correspondence in a many-body
system, and its limitations.Comment: 15 pages, 8 figure
Discovery of a Galaxy Cluster via Weak Lensing
We report the discovery of a cluster of galaxies via its weak gravitational
lensing effect on background galaxies, the first spectroscopically confirmed
cluster to be discovered through its gravitational effects rather than by its
electromagnetic radiation. This fundamentally different selection mechanism
promises to yield mass-selected, rather than baryon or photon-selected, samples
of these important cosmological probes. We have confirmed this cluster with
spectroscopic redshifts of fifteen members at z=0.276, with a velocity
dispersion of 615 km/s. We use the tangential shear as a function of source
photometric redshift to estimate the lens redshift independently and find z_l =
0.30 +- 0.08. The good agreement with the spectroscopy indicates that the
redshift evolution of the mass function may be measurable from the imaging data
alone in shear-selected surveys.Comment: revised version with minor changes, to appear in ApJ
Fragmentation and Evolution of Molecular Clouds. I: Algorithm and First Results
We present a series of simulations of the fragmentation of a molecular cloud,
leading to the formation of a cluster of protostellar cores. The purpose of
these simulations is to address a specific numerical problem called artificial
fragmentation, that plagues SPH simulations of cloud fragmentation. We argue
that this is a serious problem that needs to be addressed, and that the only
reasonable and practical way to address it is to use a relatively new technique
called particle splitting. Our largest simulation has an effective resolution
of 256^3 particles (much higher than most previous SPH simulations of cloud
fragmentation) and results in the formation of a dense cluster containing ~3000
protostellar cores. It is the first simulation of this kind to properly resolve
the Jeans mass throughout the entire system, at all times, thus preventing
artificial fragmentation.Comment: 47 pages, 15 figures (2 grayscale, one color), ApJ Suppl, in pres
Optical conductivity of the Frohlich polaron
We present accurate results for optical conductivity of the three dimensional
Frohlich polaron in all coupling regimes. The systematic-error free
diagrammatic quantum Monte Carlo method is employed where the Feynman graphs
for the momentum-momentum correlation function in imaginary time are summed up.
The real-frequency optical conductivity is obtained by the analytic
continuation with stochastic optimization. We compare numerical data with
available perturbative and non-perturbative approaches to the optical
conductivity and show that the picture of sharp resonances due to relaxed
excited states in the strong coupling regime is ``washed out''by large
broadening of these states. As a result, the spectrum contains only a
single-maximum broad peak with peculiar shape and a shoulder.Comment: 4 pages, 6 ps-figure
Increase in soil erosion after agricultural intensification: evidence from a lowland basin in France
International audienceChanges in agricultural practices impact sediment transfer in catchments and rivers. Long term archives of sediment deposits in agricultural plains of northwestern Europe are rarely available, however, for reconstructing and quantifying erosion and sedimentation rates for the second half of the 20th century. In this context, a multi-parameter analysis was conducted on sedimentary deposits accumulated in a pond created in the 11th century and draining a 24 km2 cultivated catchment in western France. This catchment is representative of cultivated and drained lowland environments where agriculture has intensified during the last 60 years.High resolution seismic profiles and surface sediment samples (n = 74) were used to guide the collection of cores (n = 3) representative of the sequence of sediment accumulated in the pond. The cores were analysed to quantify and characterize the evolution of sediment dynamics in the pond.The first land consolidation period (1954-1960) was characterized by a dominance of allochtonous material input to the pond. This input represents an erosion of 1900 to 2300 t.km−2.yr−1 originating from the catchment. Then, between 1970-1990, the terrigenous input decreased progressively and tended to stabilize. Eutrophication and associated primary production increased in the pond. These processes generated the majority of material accumulated in the pond during this period. Further land consolidation programs conducted in 1992 generated a new increase in soil erosion and sediment input to the reservoir. For the last 10 years, terrigenous input to the pond corresponds to a catchment-wide erosion rate between 90 and 102 t.km−2.yr−1. While a strong decrease is observed, it still represents a 60-fold increase of the sediment flux compared to the pre-intensification period. These large temporal variations of sedimentation rates over a few decades underline the dynamics of sediment transfer and raise questions about the sustainability of soil resources in lowland temperate environments
RXJ1716.6+6708: a young cluster at z=0.81
Clusters of galaxies at redshifts nearing one are of special importance since
they may be caught at the epoch of formation. At these high redshifts there are
very few known clusters. We present follow-up ASCA, ROSAT HRI and Keck LRIS
observations of the cluster RXJ1716.6+6708 which was discovered during the
optical identification of X-ray sources in the North Ecliptic Pole region of
the ROSAT All-Sky Survey. At z=0.809, RXJ1716.6+6708 is the second most distant
X-ray selected cluster so far published and the only one with a large number of
spectroscopically determined cluster member velocities. The optical morphology
of RXJ1716.6+6708 resembles an inverted S-shape filament with the X-rays coming
from the midpoint of the filament. The X-ray contours have an elongated shape
that roughly coincide with the weak lensing contours. The cluster has a low
temperature, kT=5.66{+1.37 -0.58} keV, and a very high velocity dispersion
sigma_{los}=1522{+215 -150} km s^{-1}. While the temperature is commensurate
with its X-ray luminosity of (8.19 +/- 0.43)x10^{44} h_{50}^{-2} erg s^{-1}
(2-10 keV rest frame), its velocity dispersion is much higher than expected
from the sigma-T_X relationship of present-day clusters with comparable X-ray
luminosity. RXJ1716.6+6708 could be an example of a protocluster, where matter
is flowing along filaments and the X-ray flux is maximum at the impact point of
the colliding streams of matter.Comment: Latex file, 18 pages, 4 figures, accepted for publication in the
Astronomical Journa
An X-ray review of MS1054-0321: hot or not?
XMM-Newton observations are presented for the z=0.83 cluster of galaxies
MS1054-0321, the highest redshift cluster in the Einstein Extended Medium
Sensitivity Survey (EMSS). The temperature inferred by the XMM-Newton data,
T=7.2 (+0.7, -0.6) keV, is much lower than the temperature previously reported
from ASCA data, T=12.3 (+3.1, -2.2) keV (Donahue et al. 1998), and a little
lower than the Chandra temperature, T=10.4(+1.7, -1.5) keV, determined by
Jeltema et al. 2001. The discrepancy between the newly derived temperature and
the previously derived temperatures is discussed in detail. If one allows the
column density to be a free parameter, then the best fit temperature becomes
T=8.6 (+1.2, -1.1) keV, and the best fit column density becomes N_(H)=1.33
(+0.15 -0.14) x 10^20 atoms/cm^2. The iron line is well detected in the
XMM-Newton spectrum with a value for the abundance of Z=0.33 (+0.19 -0.18)
Zsol, in very good agreement with previous determinations. The derived XMM
X-ray luminosity for the overall cluster in the 2-10 keV energy band is
L_X=(3.81 +/- 0.19) x 10^44 h^-2 erg s^-1 while the bolometric luminosity is
L_BOL=(8.05+/-0.40) x 10^44 h^-2 erg s^-1. The XMM-Newton data confirm the
substructure in the cluster X-ray morphology already seen by ROSAT and in much
more detail by Chandra. The central weak lensing clump is coincident with the
main cluster component and has a temperature T=8.1 (+1.3, -1.2) keV. The
western weak lensing clump coincides with the western X-ray component which is
much cooler with a temperature T=5.6 (+0.8, -0.6)$ keV. Given the newly
determined temperature, MS1054-0321 is no longer amongst the hottest clusters
known.Comment: To appear in the A&A main Journal, 13 pages including 3 postscript
figures and 4 tables. Figs. 1, 4, 5 and 7 are too large and are not given
here. The whole paper as pdf file is posted at
http://www.ira.cnr.it/~gioia/PUB/publications.htm
Riding the wake of a merging galaxy cluster
Using WHT OASIS integral field unit observations, we report the discovery of
a thin plume of ionised gas extending from the brightest cluster galaxy in
Abell 2146 to the sub-cluster X-ray cool core which is offset from the BCG by
~37 kpc. The plume is greater than 15 kpc long and less than 3 kpc wide. This
plume is unique in that the cluster it is situated in is currently undergoing a
major galaxy cluster merger. The brightest cluster galaxy is unusually located
behind the X-ray shock front and in the wake of the ram pressure stripped X-ray
cool core and evidence for recent disruption to the BCG is observed. We examine
the gas and stellar morphology, the gas kinematics of the BCG and their
relation to the X-ray gas. We propose that a causal link between the ionised
gas plume and the offset X-ray cool core provides the simplest explanation for
the formation of the plume. An interaction or merger between the BCG and
another cluster galaxy is probably the cause of the offset.Comment: 14 pages, 18 figures, accepted for publication in MNRA
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