84 research outputs found
SMAUG: a new technique for the deprojection of galaxy clusters
This paper presents a new technique for reconstructing the spatial
distributions of hydrogen, temperature and metal abundance of a galaxy cluster.
These quantities are worked out from the X-ray spectrum, modeled starting from
few analytical functions describing their spatial distributions. These
functions depend upon some parameters, determined by fitting the model to the
observed spectrum. We have implemented this technique as a new model in the
XSPEC software analysis package. We describe the details of the method, and
apply it to work out the structure of the cluster A1795. We combine the
observation of three satellites, exploiting the high spatial resolution of
Chandra for the cluster core, the wide collecting area of XMM-Newton for the
intermediate regions and the large field of view of Beppo-SAX for the outer
regions. We also test the validity and precision of our method by i) comparing
its results with those from a geometrical deprojection, ii) examining the
spectral residuals at different radii of the cluster and iii) reprojecting the
unfolded profiles and comparing them directly to the measured quantities. Our
analytical method yields the parameters defining the spatial functions directly
from the spectra. Their explicit knowledge allows a straightforward derivation
of other indirect physical quantities like the gravitating mass, as well as a
fast and easy estimate of the profiles uncertainties.Comment: 24 pages, 11 figures, 3 tables; emulateapj; accepted for publication
in the Astrophysical Journa
Radiative cooling, heating and thermal conduction in M87
The crisis of the standard cooling flow model brought about by Chandra and
XMM-Newton observations of galaxy clusters, has led to the development of
several models which explore different heating processes in order to assess if
they can quench the cooling flow. Among the most appealing mechanisms are
thermal conduction and heating through buoyant gas deposited in the ICM by
AGNs. We combine Virgo/M87 observations of three satellites (Chandra,
XMM-Newton and Beppo-SAX) to inspect the dynamics of the ICM in the center of
the cluster. Using the spectral deprojection technique, we derive the physical
quantities describing the ICM and determine the extra-heating needed to balance
the cooling flow assuming that thermal conduction operates at a fixed fraction
of the Spitzer value. We assume that the extra-heating is due to buoyant gas
and we fit the data using the model developed by Ruszkowski and Begelman
(2002). We derive a scale radius for the model of kpc, which is
comparable with the M87 AGN jet extension, and a required luminosity of the AGN
of a erg s, which is comparable to the observed AGN
luminosity. We discuss a scenario where the buoyant bubbles are filled of
relativistic particles and magnetic field responsible for the radio emission in
M87. The AGN is supposed to be intermittent and to inject populations of
buoyant bubbles through a succession of outbursts. We also study the X-ray cool
component detected in the radio lobes and suggest that it is structured in
blobs which are tied to the radio buoyant bubbles.Comment: 25 pages, 10 figures and 2 tables. Accepted for publication in Ap
A textbook example of ram-pressure stripping in the Hydra A/A780 cluster
In the current epoch, one of the main mechanisms driving the growth of galaxy clusters is the continuous accretion of group-scale halos. In this process, the ram pressure applied by the hot intracluster medium on the gas content of the infalling group is responsible for stripping the gas from its dark-matter halo, which gradually leads to the virialization of the infalling gas in the potential well of the main cluster. Using deep wide-field observations of the poor cluster Hydra A/A780 with XMM-Newton and Suzaku, we report the discovery of an infalling galaxy group 1.1 Mpc south of the cluster core. The presence of a substructure is confirmed by a dynamical study of the galaxies in this region. A wake of stripped gas is trailing behind the group over a projected scale of 760 kpc. The temperature of the gas along the wake is constant at kT ~ 1.3 keV, which is about a factor of two less than the temperature of the surrounding plasma. We observe a cold front pointing westwards compared to the peak of the group, which indicates that the group is currently not moving in the direction of the main cluster, but is moving along an almost circular orbit. The overall morphology of the group bears remarkable similarities with high-resolution numerical simulations of such structures, which greatly strengthens our understanding of the ram-pressure stripping process
Exercise-induced mitral regurgitation and right ventricle to pulmonary circulation uncoupling across the heart failure phenotypes
Exercise-induced mitral regurgitation (Ex-MR) is one of the mechanisms that contribute to reduced functional capacity in heart failure (HF). Its prevalence is not well defined across different HF subtypes. The aim of the present study was to describe functional phenotypes and cardiac response to exercise in HFrEF, HFmrEF, and HFpEF, according to Ex-MR prevalence. A total of 218 patients with HF [146 men, 68 (59â78) yr], 137 HFrEF, 41 HFmrEF, 40 HFpEF, and 23 controls were tested with cardiopulmonary exercise test combined with exercise echocardiography. Ex-MR was defined as development of at least moderate (â„2+/4+) regurgitation during exercise. Ex-MR was highly prevalent in the overall population (52%) although differed in the subgroups as follows: 82/137 (60%) in HFrEF, 17/41 (41%) in HFmrEF, and 14/40 (35%) in HFpEF (P < 0.05). Ex-MR was associated with a high rate of ventilation (VE) to carbon dioxide production (VCO2) in all HF subtypes [31.2 (26.6â35.6) vs. 33.4 (29.6â40.5), P = 0.004; 28.1 (24.5â31.9) vs. 34.4 (28.2â36.7), P = 0.01; 28.8 (26.6â32.4) vs. 32.2 (29.2â36.7), P = 0.01] and with lower peak VO2 in HFrEF and HFmrEF. Exercise right ventricle to pulmonary circulation (RV-PC) uncoupling was observed in HFrEF and HFpEF patients with Ex-MR [peak TAPSE/SPAP: HFrEF 0.40 (0.30â0.57) vs. 0.29 (0.23â0.39), P = 0.006; HFpEF 0.44 (0.28â0.62) vs. 0.31 (0.27â0.33), P = 0.05]. HFpEF with Ex-MR showed a distinct phenotype characterized by better chronotropic reserve and peripheral O2 extraction
New experimental techniques for fracture testing of highly deformable materials
A new experimental method for measuring strain fields in highly deformable materials has been developed. This technique is based on an in-house developed Digital Image Correlation (DIC) system capable of accurately capturing localized or non-uniform strain distributions. Thanks to the implemented algorithm based on a Semi-Global Matching (SGM) approach, it is possible to constraint the regularity of the displacement field in order to significantly improve the reliability of the evaluated strains, especially in highly deformable materials. Being originally introduced for Digital Surface Modelling from stereo pairs, SGM is conceived for performing a one-dimensional search of displacements between images, but here a novel implementation for 2D displacement solution space is introduced. SGM approach is compared with the previously in-house developed implementation based on a local Least Squares Matching (LSM) approach. A comparison with the open source code Ncorr and with some FEM results is also presented. The investigation using the present DIC method focuses on 2D full-field strain maps of plain and notched specimens under tensile loading made of two different highly deformable materials: hot mix asphalt and thermoplastic composites for 3D-printing applications. In the latter specimens, an elliptical hole is introduced to assess the potentiality of the method in experimentally capturing high strain gradients in mixed-mode fracture situations
X-ray characterisation of the massive galaxy clusterClG-J104803.7+313843 at z=0.76 with XMM-Newton
We present the characterisation of the massive cluster ClG-J
at performed using a serendipitous XMM-Newton observation. High
redshift and massive objects represent an ideal laboratory to benchmark our
understanding of how cluster form and assembly formation driven mainly by
gravity.Leveraging the high throughput of XMM-Newton we were firstly able to
determine the redshift of the object, shedding light on ambiguous photometric
redshift associations. We investigated the morphology of this cluster which
shows signs of merging activities in the outskirts and a flat core. We also
measured the radial density profile up to . With these quantities in
hand, we were able to determine the mass, , using the YX proxy. This quantity improves previous
measurement of the mass of this object by a factor of . The
characterisation of one cluster at such mass and redshift regime is fundamental
as these objects are intrinsically rare, the number of objects discovered so
far being less than . Our study highlights the importance of using
X-ray observations in combination with ancillary multi-wavelength data to
improve our understanding of high-z and massive clustersComment: Submitted to A&
Gas sloshing, cold fronts, Kelvin-Helmholtz instabilities and the merger history of the cluster of galaxies Abell 496
We investigate the origin and nature of the multiple sloshing cold fronts in
the core of Abell 496 by direct comparison between observations and dedicated
hydrodynamical simulations. Our simulations model a minor merger with a
4{\times}10^13M{\circ} subcluster crossing A496 from the south-west to the
north-north-east, passing the cluster core in the south-east at a pericentre
distance 100 to a few 100 kpc about 0.6 to 0.8 Gyr ago. The gas sloshing
triggered by the merger can reproduce almost all observed features, e.g. the
characteristic spiral-like brightness residual distribution in the cluster
centre and its asymmetry out to 500 kpc, also the positions of and contrasts
across the cold fronts. If the subcluster passes close (100 kpc) to the cluster
core, the resulting shear flows are strong enough to trigger Kelvin-Helmholtz
instabilities that in projection resemble the peculiar kinks in the cold fronts
of Abell 496. Finally, we show that sloshing does not lead to a significant
modification of the global ICM profiles but a mild oscillation around the
initial profiles.Comment: MNRAS, accepted, 19 page
Low heat conduction in white dwarf boundary layers?
X-ray spectra of dwarf novae in quiescence observed by Chandra and XMM-Newton
provide new information on the boundary layers of their accreting white dwarfs.
Comparison of observations and models allows us to extract estimates for the
thermal conductivity in the accretion layer and reach conclusions on the
relevant physical processes. We calculate the structure of the dense thermal
boundary layer that forms under gravity and cooling at the white dwarf surface
on accretion of gas from a hot tenuous ADAF-type coronal inflow. The
distribution of density and temperature obtained allows us to calculate the
strength and spectrum of the emitted X-ray radiation. They depend strongly on
the values of thermal conductivity and mass accretion rate. We apply our model
to the dwarf nova system VW Hyi and compare the spectra predicted for different
values of the thermal conductivity with the observed spectrum. We find a
significant deviation for all values of thermal conductivity that are a sizable
fraction of the Spitzer conductivity. A good fit arises however for a
conductivity of about 1% of the Spitzer value. This also seems to hold for
other dwarf nova systems in quiescence. We compare this result with thermal
conduction in other astrophysical situations. The highly reduced thermal
conductivity in the boundary layer requires magnetic fields perpendicular to
the temperature gradient. Locating their origin in the accretion of magnetic
fields from the hot ADAF-type coronal flow we find that dynamical effects of
these fields will lead to a spatially intermittent, localized accretion
geometry at the white dwarf surface.Comment: 8 pages, 5 figs, to appear in Astronomy & Astrophysic
Mixed Models with n>1 and Large Scale Structure constraints
Recent data on CBR anisotropies show a Doppler peak higher than expected in
CDM cosmological models, if the spectral index . However, CDM and LCDM
models with n>1 can hardly be consistent with LSS data. Mixed models, instead,
whose transfer function is naturally steeper because of free--streaming in the
hot component, may become consistent with data if n>1, when Omega_h is large.
This is confirmed by our detailed analysis, extended both to models with a hot
component whose momentum space distribution had a thermal origin (like massive
neutrinos), and to models with a non--cold component arising from heavier
particle decay. In this work we systematically search models which fulfill all
constraints which can be implemented at the linear level. We find that a
stringent linear constraint arises from fitting the extra-power parameter
Gamma. Other significant constraints arise comparing the expected abundances of
galaxy clusters and high-z systems with observational data. Keeping to models
with Gamma \geq 0.13, a suitable part of the space parameter still allows up to
\sim 30% of hot component (it is worth outlining that our stringent criteria
allow only models with 0.10 \mincir Omega_h \mincir 0.16, if n \leq 1). We also
outline that models with such large non--cold component would ease the solution
of the so--called baryon catastrophe in galaxy clusters.Comment: 28 pages + 9 figures, uses elsart.sty, to be published in New
Astronom
Non-thermal pressure support in X-COP galaxy clusters
Galaxy clusters are the endpoints of structure formation and are continuously growing through the merging and accretion of smaller structures. Numerical simulations predict that a fraction of their energy content is not yet thermalized, mainly in the form of kinetic motions (turbulence, bulk motions). Measuring the level of non-thermal pressure support is necessary to understand the processes leading to the virialization of the gas within the potential well of the main halo and to calibrate the biases in hydrostatic mass estimates. We present high-quality measurements of hydrostatic masses and intracluster gas fraction out to the virial radius for a sample of 13 nearby clusters with available XMM-Newton and Planck data. We compare our hydrostatic gas fractions with the expected universal gas fraction to constrain the level of non-thermal pressure support. We find that hydrostatic masses require little correction and infer a median non-thermal pressure fraction of âŒ6% and âŒ10% at R500 and R200, respectively. Our values are lower than the expectations of hydrodynamical simulations, possibly implying a faster thermalization of the gas. If instead we use the mass calibration adopted by the Planck team, we find that the gas fraction of massive local systems implies a mass bias 1 â b = 0.85 ± 0.05 for Sunyaevâ Zeldovich-derived masses, with some evidence for a mass-dependent bias. Conversely, the high bias required to match Planck cosmic microwave background and cluster count cosmology is excluded by the data at high significance, unless the most massive halos are missing a substantial fraction of their baryons
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