1,667 research outputs found
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
Relativistic plasma and ICM/radio source interaction
The first detection of a diffuse radio source in a cluster of galaxies, dates
back to the 1959 (Coma Cluster, Large et al. 1959). Since then, synchrotron
radiating radio sources have been found in several clusters, and represent an
important cluster component which is linked to the thermal gas. Such sources
indicate the existence of large scale magnetic fields and of a population of
relativistic electrons in the cluster volume. The observational results provide
evidence that these phenomena are related to turbulence and shock-structures in
the intergalactic medium, thus playing a major role in the evolution of the
large scale structure in the Universe. The interaction between radio sources
and cluster gas is well established in particular at the center of cooling core
clusters, where feedback from AGN is a necessary ingredient to adequately
describe the formation and evolution of galaxies and host clusters.Comment: 8 pages, Review talk at the 274 IAU Symposium "Advances in Plasma
Astrophysics", 6-10 Sept 2010, Giardini Naxos, Italy, A. Bonanno, E. de
Gouveia Dal Pino and A. Kosovichev, ed
Improved pregnancy outcome in patients with Rheumatoid Arthritis who followed an ideal clinical pathway
Among women with rheumatoid arthritis (RA) we aimed to assess the effect of optimal management of pregnancy, on a composite outcome of miscarriage and complicated birth
Combining survey data with single-dish observations
Sky surveys represent a fundamental data source for astronomy. Radio surveys, as well as pointed observations, performed with interferometers might be affected by the so-called zero-spacing
problem when observing extended sources at relatively high frequencies. This problem cause
the most extended features in the source to be filtered out due to the lack of antenna-pairs with
small separations. Here we show that interferometric survey data can be successfully combined
with pointed observations performed with a single-dish telescope to produce images with high
resolution and correct total power information.Sky surveys represent a fundamental data source for astronomy. Radio surveys, as well as pointed
observations, performed with interferometers might be affected by the so-called zero-spacing
problem when observing extended sources at relatively high frequencies. This problem cause
the most extended features in the source to be filtered out due to the lack of antenna-pairs with
small separations. Here we show that interferometric survey data can be successfully combined
with pointed observations performed with a single-dish telescope to produce images with high
resolution and correct total power information
Magnetic fields in galaxy clusters in the SKA era
The study of the polarization of faint diffuse synchrotron sources, named radio halos, found in some galaxy clusters, is of paramount importance to characterize large scale magnetic fields. This is an hard task with the current radio telescopes but a next generation radio interferometer, the Square Kilometre Array (SKA), could help to shed light on the origin of cosmic magnetism. Thanks to its sensitivity, its broader bandwidth and its resolution, the SKA will allow us to perform complete and accurate studies of magnetic fields in clusters. In order to explore the potentiality of the SKA, we used state-of-art magneto-hydro-dynamical numerical simulations to produce synthetic maps of radio halos, taking into account the expected performances of the SKA1-MID in the radio band from 350 to 1050 MHz. Starting from the resulting maps, we were able to verify that radio halos could be intrinsically polarized and that SKA1-MID could detect their polarization, crucial to constraining the properties of large scale magnetic fields
Spectral Index of the Filaments in the Abell 523 Radio Halo
The galaxy cluster Abell 523 hosts a radio halo characterized by the presence of two filaments transversely located with respect to the cluster merger axis. In this paper, we present a spectral index image of these filaments between 1.410 and 1.782 GHz obtained with Jansky Very Large Array observations. We find a steepening of the spectral index of the filaments at frequencies 1.4 GHz and an indication that bright patches are characterized by flat spectral indices. Our results are consistent with a scenario of highly-efficient turbulence induced by merger phenomena
Puzzling large-scale polarization in the galaxy cluster Abell 523
Large-scale magnetic fields reveal themselves through diffuse synchrotron
sources observed in galaxy clusters such as radio halos. Total intensity
filaments of these sources have been observed in polarization as well, but only
in three radio halos out of about one hundred currently known. In this paper we
analyze new polarimetric Very Large Array data of the diffuse emission in the
galaxy cluster Abell 523 in the frequency range 1-2 GHz. We find for the first
time evidence of polarized emission on scales of ~ 2.5 Mpc. Total intensity
emission is observed only in the central part of the source, likely due to
observational limitations. To look for total intensity emission beyond the
central region, we combine these data with single-dish observations from the
Sardinia Radio Telescope and we compare them with multi-frequency total
intensity observations obtained with different instruments, including the LOw
Frequency ARray and the Murchison Widefield Array. By analysing the rotation
measure properties of the system and utilizing numerical simulations, we infer
that this polarized emission is associated with filaments of the radio halo
located in the outskirts of the system, in the peripheral region closest to the
observer.Comment: 14 pages, 12 figures, accepted for publication on MNRA
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