416 research outputs found
Enrichment of the hot intracluster medium: observations
Four decades ago, the firm detection of an Fe-K emission feature in the X-ray
spectrum of the Perseus cluster revealed the presence of iron in its hot
intracluster medium (ICM). With more advanced missions successfully launched
over the last 20 years, this discovery has been extended to many other metals
and to the hot atmospheres of many other galaxy clusters, groups, and giant
elliptical galaxies, as evidence that the elemental bricks of life -
synthesized by stars and supernovae - are also found at the largest scales of
the Universe. Because the ICM, emitting in X-rays, is in collisional ionisation
equilibrium, its elemental abundances can in principle be accurately measured.
These abundance measurements, in turn, are valuable to constrain the physics
and environmental conditions of the Type Ia and core-collapse supernovae that
exploded and enriched the ICM over the entire cluster volume. On the other
hand, the spatial distribution of metals across the ICM constitutes a
remarkable signature of the chemical history and evolution of clusters, groups,
and ellipticals. Here, we summarise the most significant achievements in
measuring elemental abundances in the ICM, from the very first attempts up to
the era of XMM-Newton, Chandra, and Suzaku and the unprecedented results
obtained by Hitomi. We also discuss the current systematic limitations of these
measurements and how the future missions XRISM and Athena will further improve
our current knowledge of the ICM enrichment.Comment: 49 pages. Review paper. Accepted for publication on Space Science
Reviews. This is the companion review of "Enrichment of the hot intracluster
medium: numerical simulations
The incidence of haemorrhagic and thromboembolic events after breast cancer surgery in patients treated with pharmacological thromboprophylaxis
Background. Hemorrhagic events and venous thromboembolic disease, including pulmonary embolism and deep venous thrombosis, are the most important complications after breast cancer surgery. Although hemorrhagic complications are not usually severe and do not have a high mortality risk, venous thromboembolic disease is often associated with high morbidity and mortality rates. Under such circumstances, it is highly important to evaluate the need for systemic antithrombotic prophylaxis as opposed to mechanical interventions and the optimal duration of chemoprophylaxis in patients undergoing breast cancer surgery. Methods. Using the database of the General Surgery Department of “Colţea” Clinical Hospital, we analyzed the data from 2015 to 2018. During this period, pharmacological prophylaxis was used in all patients undergoing breast cancer surgery. Mechanical prophylaxis (intermittent pneumatic compression or graduated compression) has also been recommended, but there was no record of patient compliance. The primary outcome was the occurrence of venous thromboembolic or hemorrhagic events within 30 days after surgery. Results. In our institution, the venous thromboembolic disease rate for breast cancer surgery was 4/540 (0.7%; 95% CI: 0.02-1.9%), being similar to that of other studies. Hemorrhagic events occurred in 29 (5.4%; 95% CI 3.6-7.6%) patients, most commonly as hematoma in 3.3% of the patients. The incidence of hematoma requiring operation was 1.1% (95% CI: 0.4-2.4%), while hematoma treated conservatively was 2.2% (95% CI:1.2-3.8%). Other forms of hemorrhagic events include hemorrhagic drainage and bleeding wound, occurring in 2.0% of the cases. Conclusions. The occurrence of venous thromboembolic events is reduced among patients undergoing primary breast cancer surgery. A current issue is decreasing venous thromboembolic disease rates without increasing the hemorrhagic event rate. Standard guidelines on the antithrombotic prophylaxis of these patients are not well established since studies show contradictory data. Further investigations are needed to determine exactly which type of thromboprophylaxis is more effective
Multiple-scattering effects on incoherent neutron scattering in glasses and viscous liquids
Incoherent neutron scattering experiments are simulated for simple dynamic
models: a glass (with a smooth distribution of harmonic vibrations) and a
viscous liquid (described by schematic mode-coupling equations). In most
situations multiple scattering has little influence upon spectral
distributions, but it completely distorts the wavenumber-dependent amplitudes.
This explains an anomaly observed in recent experiments
Magnetic Fields, Relativistic Particles, and Shock Waves in Cluster Outskirts
It is only now, with low-frequency radio telescopes, long exposures with
high-resolution X-ray satellites and gamma-ray telescopes, that we are
beginning to learn about the physics in the periphery of galaxy clusters. In
the coming years, Sunyaev-Zeldovich telescopes are going to deliver further
great insights into the plasma physics of these special regions in the
Universe. The last years have already shown tremendous progress with detections
of shocks, estimates of magnetic field strengths and constraints on the
particle acceleration efficiency. X-ray observations have revealed shock fronts
in cluster outskirts which have allowed inferences about the microphysical
structure of shocks fronts in such extreme environments. The best indications
for magnetic fields and relativistic particles in cluster outskirts come from
observations of so-called radio relics, which are megaparsec-sized regions of
radio emission from the edges of galaxy clusters. As these are difficult to
detect due to their low surface brightness, only few of these objects are
known. But they have provided unprecedented evidence for the acceleration of
relativistic particles at shock fronts and the existence of muG strength fields
as far out as the virial radius of clusters. In this review we summarise the
observational and theoretical state of our knowledge of magnetic fields,
relativistic particles and shocks in cluster outskirts.Comment: 34 pages, to be published in Space Science Review
Fast magnetic field amplification in distant galaxy clusters
In the present-day Universe, magnetic fields pervade galaxy clusters1 and have strengths of a few microgauss, as measured from Faraday rotation2. Evidence for cluster magnetic fields is also provided by the observation of megaparsec-scale radio emission, namely radio halos and relics3. These are commonly found in merging systems4 and are characterized by a steep radio spectrum Sν (α < −1, where Sν ∝ να and is ν the observing frequency). It is widely believed that magneto-hydrodynamical turbulence and shock waves (re-)accelerate cosmic rays5 and produce radio halos and relics. The origin and amplification of magnetic fields in clusters is not well understood. It has been proposed that turbulence drives a small-scale dynamo6–11 that amplifies seed magnetic fields (which are primordial and/or injected by galactic outflows, such as active galactic nuclei, starbursts or winds12). At high redshift, radio halos are expected to be faint, owing to losses from inverse Compton scattering and the dimming effect with distance. Moreover, Faraday rotation measurements are difficult to obtain. If detected, distant radio halos provide an alternative tool to investigate magnetic field amplification. Here, we report Low Frequency Radio Array observations that reveal diffuse radio emission in massive clusters when the Universe was only half of its present age, with a sample occurrence fraction of about 50%. The high radio luminosities indicate that these clusters have similar magnetic field strengths to those in nearby clusters, and suggest that magnetic field amplification is fast during the first phases of cluster formation
The Planck clusters in the LOFAR sky: IV: LoTSS-DR2: statistics of radio halos and re-acceleration models
Diffuse cluster-scale synchrotron radio emission is discovered in an
increasing number of galaxy clusters in the form of radio halos (RHs), probing
the presence of relativistic electrons and magnetic fields in the intra-cluster
medium. The favoured scenario to explain their origin is that they trace
turbulent regions generated during cluster mergers where particles are
re-accelerated. In this framework, RHs are expected to probe cluster dynamics
and are predicted to be more frequent in massive systems. Statistical studies
are important to study the connection of RHs with cluster dynamics and to
constrain theoretical models. Furthermore, low-frequency surveys can shed light
on the existence of RHs with very steep radio-spectra, a key prediction of
turbulent models. We study the properties of RHs from clusters of the second
catalog of Planck Sunyaev Zel'dovich detected sources that lie within the 5634
deg^2 covered by the second Data Release (DR2) of the LOFAR Two-meter Sky
Survey. We find that the number of observed RHs, their radio flux density and
redshift distributions are in line with what is expected in the framework of
the re-acceleration scenario. In addition, the fraction of clusters with RHs
increases with the cluster mass, confirming the leading role of the
gravitational process of cluster formation in the generation of RHs. These
models predict a large fraction of RHs with very steep spectrum in the DR2
Planck sample, this will be tested in future studies, yet a comparison of the
occurrence of halos in GMRT and LOFAR samples indeed shows a larger occurrence
of RHs at lower frequencies suggesting the presence of a number of very steep
spectrum RH that is preferentially detected by LOFAR. Using morphological
information we confirm that RHs are preferentially located in merging systems
and that the fraction of newly LOFAR discovered RHs is larger in less disturbed
systems.Comment: 12 pages, 10 figures, accepted for publication in A&
The Planck clusters in the LOFAR sky. III. LoTSS-DR2: Dynamic states and density fluctuations of the intracluster medium
The footprint of LoTSS-DR2 covers 309 PSZ2 galaxy clusters, 83 of which host
a radio halo and 26 host a radio relic(s). It provides us an excellent
opportunity to statistically study the properties of extended cluster radio
sources, especially their connection with merging activities. We aim to
quantify cluster dynamic states to investigate their relation with the
occurrence of extended radio sources. We also search for connections between
intracluster medium (ICM) turbulence and nonthermal characteristics of radio
halos in the LoTSS-DR2. We analyzed XMM-Newton and Chandra archival X-ray data
and computed concentration parameters and centroid shifts that indicate the
dynamic states of the clusters. We also performed a power spectral analysis of
the X-ray surface brightness (SB) fluctuations to investigate large-scale
density perturbations and estimate the turbulent velocity dispersion. The power
spectral analysis results in a large scatter density fluctuation amplitude. We
therefore only found a marginal anticorrelation between density fluctuations
and cluster relaxation state, and we did not find a correlation between density
fluctuations and radio halo power. Nevertheless, the injected power for
particle acceleration calculated from turbulent dissipation is correlated with
the radio halo power, where the best-fit unity slope supports the turbulent
(re)acceleration scenario. Two different acceleration models, transit-time
damping and adiabatic stochastic acceleration, cannot be distinguished due to
the large scatter of the estimated turbulent Mach number. We introduced a new
quantity , which is proportional to the
turbulent acceleration power assuming a constant Mach number. This quantity is
strongly correlated with radio halo power, where the slope is also unity.Comment: 20 pages, 13 figures, 5 tables includig appendix. Accepted for
publication in A&A. The abstract on arXiv has been shorten to meet the word
limi
The beautiful mess in Abell 2255
© 2020. The American Astronomical Society. All rights reserved. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.3847/1538-4357/ab9a2fWe present LOFAR observations of one of the most spectacular objects in the radio sky: Abell 2255. This is a nearby () merging galaxy cluster hosting one of the first radio halos ever detected in the intra-cluster medium (ICM). The deep LOFAR images at 144 MHz of the central Mpc region show a plethora of emission on different scales, from tens of kpc to above Mpc sizes. In this work, we focus on the innermost region of the cluster. Among the numerous interesting features observed, we discover remarkable bright and filamentary structures embedded in the radio halo. We incorporate archival WSRT 1.2 GHz data to study the spectral properties of the diffuse synchrotron emission and find a very complex spectral index distribution in the halo spanning a wide range of values. We combine the radio data with Chandra observations to investigate the connection between the thermal and non-thermal components by quantitatively comparing the radio and X-ray surface brightness and the spectral index of the radio emission with the thermodynamical quantities of the ICM. Despite the multitude of structures observed in the radio halo, we find that the X-ray and radio emission are overall well correlated. The fact that the steepest spectrum emission is located in the cluster center and traces regions with high entropy possibly suggests the presence of seed particles injected by radio galaxies that are spread in the ICM by turbulence generating the extended radio halo.Peer reviewe
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