67 research outputs found
Spectral and polarization study of the double relics in Abell 3376 using the GMRT and the VLA
Double radio relics in galaxy clusters are rare phenomena that trace shocks
in the outskirts of merging galaxy clusters. We have carried out a spectral and
polarization study of the spectacular double relics in the galaxy cluster A3376
using the Giant Metrewave Radio Telescope at 150 and 325 MHz and the Very Large
Array at 1400 MHz. The polarization study at 1400 MHz reveals a high degree of
polarization (~30%) and aligned magnetic field vectors (not corrected for
Faraday rotation) in the eastern relic. A highly polarized (>60%) filamentary
radio source of size ~300 kpc near the eastern relic and north of the bent-jet
radio galaxy is detected for the first time. The western relic is less
polarized and does not show aligned magnetic field vectors. The distribution of
spectral indices between 325 and 1400 MHz over the radio relics show steepening
from the outer to the inner edges of the relics. The spectral indices of the
eastern and the western relics imply Mach numbers in the range 2.2 to 3.3.
Remarkable features such as the inward filament extending from the eastern
relic, the highly polarized filament, the complex polarization properties of
the western relic and the separation of the BCG from the ICM by a distance >900
kpc are noticed in the cluster. A comparison with simulated cluster mergers is
required to understand the complex properties of the double relics in the
context of the merger in A3376. An upper limit (log(P(1.4GHz) W/Hz < 23.0) on
the strength of a Mpc size radio halo in A3376 is estimated.Comment: 9 pages, 4 figures, accepted for publication in MNRA
Using double radio relics to constrain galaxy cluster mergers: A model of double radio relics in CIZA J2242.8+5301
Galaxy clusters grow by mergers with other clusters and galaxy groups. These
mergers create shock waves within the intracluster medium (ICM) that can
accelerate particles to extreme energies. In the presence of magnetic fields,
relativistic electrons form large regions emitting synchrotron radiation,
so-called radio relics. Behind the shock front, synchrotron and inverse Compton
(IC) losses cause the radio spectral index to steepen away from the shock
front. An example of such a cluster is CIZA J2242.8+5301, where very clear
spectral steepening in the downstream region is observed. Here we present
hydrodynamical simulations of idealized binary cluster mergers with the aim of
constraining the merger scenario for this cluster. From our simulations, we
find that CIZA J2242.8+5301 is probably undergoing a merger in the plane of the
sky (less then 10 deg from edge-on) with a mass ratio of about 2:1, and an
impact parameter < 400 kpc. We find that the core passage of the clusters
happened about 1 Gyr ago. We conclude that double relics relics can set
constraints on the mass ratios, impact parameters, timescales, and viewing
geometry of binary cluster mergers, which is particularly useful when detailed
X-ray observations are not available. In addition, the presence of large radio
relics can be used to constrain the degree of clumping in the outskirts of the
ICM, which is important to constrain the baryon fraction, density and entropy
profiles, around the virial radius and beyond. We find that the amplitude of
density fluctuations, with sizes of < 200 kpc, in the relic in CIZA
J2242.8+5301 is not larger than 30%. [abridged]Comment: 14 pages, 8 figures, accepted for publication in MNRAS on July 20,
201
Continuous versus discrete data analysis for gait evaluation of horses with induced bilateral hindlimb lameness
Background Gait kinematics measured during equine gait analysis are typically evaluated by analysing (asymmetry-based) discrete variables (eg, peak values) obtained from continuous kinematic signals (eg, timeseries of datapoints). However, when used for the assessment of complex cases of lameness, such as bilateral lameness, discrete variable analysis might overlook relevant functional adaptations. Objectives The overall aim of this paper is to compare continuous and discrete data analysis techniques to evaluate kinematic gait adaptations to lameness. Study design Method comparison. Methods Sixteen healthy Shetland ponies, enrolled in a research programme in which osteochondral defects were created on the medial trochlear ridges of both femurs, were used in this study. Kinematic data were collected at trot on a treadmill before and at 3 and 6 months after surgical intervention. Statistical parametric mapping and linear mixed models were used to compare kinematic variables between and within timepoints. Results Both continuous and discrete data analyses identified changes in pelvis and forelimb kinematics. Discrete data analyses showed significant changes in hindlimb and back kinematics, where such differences were not found to be significant by continuous data analysis. In contrast, continuous data analysis provided additional information on the timing and duration of the differences found. Main limitations A limited number of ponies were included. Conclusions The use of continuous data provides additional information regarding gait adaptations to bilateral lameness that is complementary to the analysis of discrete variables. The main advantage lies in the additional information regarding time dependence and duration of adaptations, which offers the opportunity to identify functional adaptations during all phases of the stride cycle, not just the events related to peak values
Radio relics in cosmological simulations
Radio relics have been discovered in many galaxy clusters. They are believed
to trace shock fronts induced by cluster mergers. Cosmological simulations
allow us to study merger shocks in detail since the intra-cluster medium is
heated by shock dissipation. Using high resolution cosmological simulations,
identifying shock fronts and applying a parametric model for the radio emission
allows us to simulate the formation of radio relics. We analyze a simulated
shock front in detail. We find a rather broad Mach number distribution. The
Mach number affects strongly the number density of relativistic electrons in
the downstream area, hence, the radio luminosity varies significantly across
the shock surface. The abundance of radio relics can be modeled with the help
of the radio power probability distribution which aims at predicting radio
relic number counts. Since the actual electron acceleration efficiency is not
known, predictions for the number counts need to be normalized by the observed
number of radio relics. For the characteristics of upcoming low frequency
surveys we find that about thousand relics are awaiting discovery.Comment: 10 pages, 4 figures, Invited talk at the conference "Diffuse
Relativistic Plasmas", Bangalore, 1-4 March 2011; in press in special issue
of Journal of Astrophysics and Astronom
История возникновения католической общины города Севастополя и строительство римско-католического костёла
Цель статьи – проследить этапы формирования римско-католической общины города Севастополя и историю строительства римско-католического костёла во имя Священномученника Климента Римского
A low-frequency radio halo survey of the South Pole Telescope SZ-selected clusters with the GMRT
Large scale structure and cosmolog
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