6,858 research outputs found
Detection of diffuse radio emission in the galaxy clusters A800, A910, A1550, and CL1446+26
Radio halos are elusive sources located at the center of merging galaxy
clusters. To date, only about 40 radio halos are known, thus the discovery of
new halos provide important insights on this class of sources. To improve the
statistics of radio halos, we investigated the radio continuum emission in a
sample of galaxy clusters. We analyzed archival Very Large Array observations
at 1.4 GHz, with a resolution of about 1 arcmin. These observations
complemented by X-ray, optical, and higher resolution radio data allowed to
detect a new radio halo in the central region of A800 and A1550. We discovered
a radio relic in the periphery of A910, and finally we revealed both a halo and
a relic in CL1446+26.Clusters hosting these new halos show an offset between
the radio and the X-ray peak. By analyzing this offset statistically we found
that radio halos can be quite asymmetric with respect to the X-ray gas
distribution, with an average radio - X-ray displacement of about 180 kpc. When
the offsets are normalized by the halo size, there is a tendency for smaller
halos to show larger displacements.Comment: Accepted by Astronomy and Astrophysics, 13 pages, 8 figure
Unravelling the origin of large-scale magnetic fields in galaxy clusters and beyond through Faraday Rotation Measures with the SKA
We investigate the possibility for the SKA to detect and study the magnetic
fields in galaxy clusters and in the less dense environments surrounding them
using Faraday Rotation Measures. To this end, we produce 3-dimensional magnetic
field models for galaxy clusters of different masses and in different stages of
their evolution, and derive mock rotation measure observations of background
radiogalaxies. According to our results, already in phase I, we will be able to
infer the magnetic field properties in galaxy clusters as a function of the
cluster mass, down to solar-masses. Moreover, using cosmological
simulations to model the gas density, we have computed the expected rotation
measure through shock-fronts that occur in the intra-cluster medium during
cluster mergers. The enhancement in the rotation measure due to the density
jump will permit to constraint the magnetic field strength and structure after
the shock passage. SKA observations of polarised sources located behind galaxy
clusters will answer several questions about the magnetic field strength and
structure in galaxy clusters, and its evolution with cosmic time.Comment: 9 pages, 4 Figures, to appear as part of 'Cosmic Magnetism' in
Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14
Comparisons of Cosmological MHD Galaxy Cluster Simulations to Radio Observations
Radio observations of galaxy clusters show that there are G magnetic
fields permeating the intra-cluster medium (ICM), but it is hard to accurately
constrain the strength and structure of the magnetic fields without the help of
advanced computer simulations. We present qualitative comparisons of synthetic
VLA observations of simulated galaxy clusters to radio observations of Faraday
Rotation Measure (RM) and radio halos. The cluster formation is modeled using
adaptive mesh refinement (AMR) magneto-hydrodynamic (MHD) simulations with the
assumption that the initial magnetic fields are injected into the ICM by active
galactic nuclei (AGNs) at high redshift. In addition to simulated clusters in
Xu et al. (2010, 2011), we present a new simulation with magnetic field
injections from multiple AGNs. We find that the cluster with multiple injection
sources is magnetized to a similar level as in previous simulations with a
single AGN. The RM profiles from simulated clusters, both and the
dispersion of RM (), are consistent at a first-order with the
radial distribution from observations. The correlations between the
and X-ray surface brightness from simulations are in a broad
agreement with the observations, although there is an indication that the
simulated clusters could be slightly over-dense and less magnetized with
respect to those in the observed sample. In addition, the simulated radio halos
agree with the observed correlations between the radio power versus the cluster
X-ray luminosity and between the radio power versus the radio halo size. These
studies show that the cluster wide magnetic fields that originate from AGNs and
are then amplified by the ICM turbulence (Xu et al. 2010) match observations of
magnetic fields in galaxy clusters.Comment: Accepted for publication in Ap
A Chandra View of the Multiple Merger In Abell 2744
We present a Chandra observation of the merging cluster of galaxies Abell
2744. The cluster shows strong evidence for an ongoing major merger which we
believe to be responsible for the radio halo. X-ray emission and temperature
maps of the cluster, combined with the spatial and redshift distribution of the
galaxies, indicate a roughly north-south axis for the merger, with a
significant velocity component along the line of sight. The merger is occurring
at a very large velocity, with M = 2-3. In addition, there is a small merging
subcluster toward the northwest, unrelated to the major merger, which shows
evidence of a bow shock. A hydrodynamical analysis of the subcluster indicates
a merger velocity corresponding to a Mach number of ~1.2, consistent with a
simple infall model. This infalling subcluster may also be re-exciting
electrons in the radio halo. Its small Mach number lends support to turbulent
reacceleration models for radio halo formation.Comment: 8 pages, 6 figures (5 color). Submitted to MNRA
Hyaluronan and cardiac regeneration
Hyaluronan (HA) is abundantly expressed in several human tissues and a variety of roles for HA has been highlighted. Particularly relevant for tissue repair, HA is actively produced during tissue injury, as widely evidenced in wound healing investigations. In the heart HA is involved in physiological functions, such as cardiac development during embryogenesis, and in pathological conditions including atherosclerosis and myocardial infarction. Moreover, owing to its relevant biological properties, HA has been widely used as a biomaterial for heart regeneration after a myocardial infarction. Indeed, HA and its derivatives are biodegradable and biocompatible, promote faster healing of injured tissues, and support cells in relevant processes including survival, proliferation, and differentiation. Injectable HA-based therapies for cardiovascular disease are gaining growing attention because of the benefits obtained in preclinical models of myocardial infarction. HA-based hydrogels, especially as a vehicle for stem cells, have been demonstrated to improve the process of cardiac repair by stimulating angiogenesis, reducing inflammation, and supporting local and grafted cells in their reparative functions. Solid-state HA-based scaffolds have been also investigated to produce constructs hosting mesenchymal stem cells or endothelial progenitor cells to be transplanted onto the infarcted surface of the heart. Finally, applying an ex-vivo mechanical stretching, stem cells grown in HA-based 3D scaffolds can further increase extracellular matrix production and proneness to differentiate into muscle phenotypes, thus suggesting a potential strategy to create a suitable engineered myocardial tissue for cardiac regeneration
5'-deiodinase activity and circulating thyronines in lactating cows.
To investigate the correlation between lactation and thyroid hormone metabolism, the authors studied concentrations of total and free thyroxine (T4 and fT4), triiodothyronine (T3 and fT3), and reverse triiodothyronine (rT3) in plasma and milk, as well as liver and mammary gland 5'-deiodinase (5'D) activity in dry, early, middle, and late lactating dairy cows. Cows in early lactation show lower plasma levels of T4 and rT3 than dry, middle, and late lactating animals, whereas T3 shows the lowest plasma levels in the dry period; free T4 and T3 show a similar pattern. In early lactation there is a clear decrease in liver 5'D associated with a notable increase in mammary 5'D. Concentrations of T4 and T3 in milk drop significantly in the first few days after delivery, whereas rT3 increases up to the fourth month. The findings suggest a relationship between the hypothyroid status of lactating cows and the rearrangement of organ-specific 5'-deiodinase activity related to the maintenance of the udder's function
Observations of extended radio emission in clusters
We review observations of extended regions of radio emission in clusters;
these include diffuse emission in `relics', and the large central regions
commonly referred to as `halos'. The spectral observations, as well as Faraday
rotation measurements of background and cluster radio sources, provide the main
evidence for large-scale intracluster magnetic fields and significant densities
of relativistic electrons. Implications from these observations on acceleration
mechanisms of these electrons are reviewed, including turbulent and shock
acceleration, and also the origin of some of the electrons in collisions of
relativistic protons by ambient protons in the (thermal) gas. Improved
knowledge of non-thermal phenomena in clusters requires more extensive and
detailed radio measurements; we briefly review prospects for future
observations.Comment: 27 pages, 7 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 6; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
GMRT observations of the Ophiuchus galaxy cluster
VLA observations at 1477 MHz revealed the presence of a radio mini-halo
surrounding the faint central point-like radio source in the Ophiuchus cluster
of galaxies. In this work we present a study of the radio emission from this
cluster of galaxies at lower radio frequencies. We observed the Ophiuchus
cluster at 153, 240, and 614 MHz with the GMRT. The mini-halo is clearly
detected at 153 and 240 MHz while it is not detected at 610 MHz. The most
prominent feature at low frequencies is a patch of diffuse steep spectrum
emission located at about 5' south-east from the cluster center. By combining
these images with that at 1477 MHz, we derived the spectral index of the
mini-halo. Globally, the mini-halo has a low-frequency spectral index of
alpha_240^153 ~1.4 +/- 0.3 and an high-frequency spectral index of
alpha_1477^240 ~ 1.60 +/- 0.05. Moreover, we measure a systematic increase of
the high-frequency spectral index with radius: the azimuthal radial average of
alpha_1477^240 increases from about 1.3, at the cluster center, up to about 2.0
in the mini-halo outskirts. The observed radio spectral index is in agreement
with that obtained by modeling the non-thermal hard X-ray emission in this
cluster of galaxies. We assume that the X-ray component arises from inverse
Compton scattering between the photons of the cosmic microwave background and a
population of non-thermal electrons which are isotropically distributed and
whose energy spectrum is a power law with index p. We derive that the electrons
energy spectrum should extend from a minimum Lorentz factor of gamma_min < 700
up to a maximum Lorentz factor of gamma_max =3.8 x 10^4 with an index p=3.8 +/-
0.4. The volume-averaged strength for a completely disordered intra-cluster
magnetic field is B_V ~0.3 +/- 0.1 micro-G.Comment: 14 pages, 8 figures, accepted for publication in Astronomy and
Astrophysics. For a version with high-quality figures see
http://erg.ca.astro.it/preprints/ophi_2010
Same Sign WW Scattering Process as a Probe of Higgs Boson in pp Collision at = 10 TeV
WW scattering is an important process to study electroweak symmetry breaking
in the Standard Model at the LHC, in which the Higgs mechanism or other new
physics processes must intervene to preserve the unitarity of the process below
1 TeV. This channel is expected to be one of the most sensitive to determine
whether the Higgs boson exists. In this paper, the final state with two same
sign Ws is studied, with a simulated sample corresponding to the integrated
luminosity of 60 fb in pp collision at 10 TeV. Two
observables, the invariant mass of from W decays and the azimuthal
angle difference between the two s, are utilized to distinguish the Higgs
boson existence scenario from the Higgs boson absence scenario. A good signal
significance for the two cases can be achieved. If we define the separation
power of the analysis as the distance, in the log-likelihood plane, of
pseudo-experiments outcomes in the two cases, with the total statistics
expected from the ATLAS and CMS experiments at the nominal centre-of-mass
energy of 14 TeV, the separation power will be at the level of 4 .Comment: 5 pages, 4 figures, 3 table
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