Galaxy clusters are unique laboratories to investigate turbulent fluid motions and large scale magnetic fields. Synchrotron radio halos at the center of merging galaxy clusters provide the most spectacular and direct evidence of the presence of relat
ivistic particles and magnetic fields associated with the intracluster medium. The study of polarized emission from radio halos is extremely important to constrain the properties of intracluster magnetic fields and the physics of the acceleration and transport of the relativistic particles. However, detecting this polarized signal is a very hard task with the current radio facilities.We use cosmological magneto-hydrodynamical simulations to predict the expected polarized surface brightness of radio halos at 1.4 GHz. We compare these expectations with the sensitivity and the resolution reachable with the SKA1. This allows us to evaluate the potential for studying intracluster magnetic fields in the surveys planned for SKA1.
Synchrotron radio halos at the center of merging galaxy clusters provide the most spectacular and direct evidence of the presence of relativistic particles and magnetic fields associated with the intracluster medium. The study of polarized emission f
rom radio halos has been shown to be extremely important to constrain the properties of intracluster magnetic fields. However, detecting this polarized signal is a very hard task with the current radio facilities.We investigate whether future radio observatories, such as the Square Kilometer Array (SKA) and its precursors and pathfinders, will be able to detect the polarized emission of radio halos in galaxy clusters.On the basis of cosmological magnetohydrodynamical simulations with initial magnetic fields injected by active galactic nuclei, we predict the expected radio halo polarized signal at 1.4 GHz. We compare these expectations with the limits of current radio facilities and explore the potential of the forthcoming radio interferometers to investigate intracluster magnetic fields through the detection of polarized emission from radio halos.The resolution and sensitivity values that are expected to be obtained in future sky surveys performed at 1.4 GHz using the SKA precursors and pathfinders (like APERTIF and ASKAP) are very promising for the detection of the polarized emission of the most powerful (L1.4GHz>10e25 Watt/Hz) radio halos. Furthermore, the JVLA have the potential to already detect polarized emission from strong radio halos, at a relatively low resolution.However, the possibility of detecting the polarized signal in fainter radio halos (L1.4GHz~10e24 Watt/Hz) at high resolution requires a sensitivity reachable only with SKA.
The dying radio sources represent a very interesting and largely unexplored stage of the active galactic nucleus (AGN) evolution. They are considered to be very rare, and almost all of the few known ones were found in galaxy clusters. However, consid
ering the small number detected so far, it has not been possible to draw any firm conclusions about their X-ray environment. We present X-ray observations performed with the Chandra satellite of the three galaxy clusters Abell 2276, ZwCl 1829.3+6912, and RX J1852.1+5711, which harbor at their center a dying radio source with an ultra-steep spectrum that we recently discovered. We analyzed the physical properties of the X-ray emitting gas surrounding these elusive radio sources. We determined the global X-ray properties of the clusters, derived the azimuthally averaged profiles of metal abundance, gas temperature, density, and pressure. Furthermore, we estimated the total mass profiles. The large-scale X-ray emission is regular and spherical, suggesting a relaxed state for these systems. Indeed, we found that the three clusters are also characterized by significant enhancements in the metal abundance and declining temperature profiles toward the central region. For all these reasons, we classified RX J1852.1+5711, Abell 2276, and ZwCl 1829.3+6912 as cool-core galaxy clusters.
The aim of this work is to investigate the average properties of the intra-cluster medium (ICM) magnetic fields, and to search for possible correlations with the ICM thermal properties and cluster radio emission. We have selected a sample of 39 massi
ve galaxy clusters from the HIghest X-ray FLUx Galaxy Cluster Sample, and used Northern VLA Sky Survey data to analyze the fractional polarization of radio sources out to 10 core radii from the cluster centers. Following Murgia et al (2004), we have investigated how different magnetic field strengths affect the observed polarized emission of sources lying at different projected distances from the cluster center. In addition, statistical tests are performed to investigate the fractional polarization trends in clusters with different thermal and non-thermal properties. We find a trend of the fractional polarization with the cluster impact parameter, with fractional polarization increasing at the cluster periphery and decreasing toward the cluster center. Such trend can be reproduced by a magnetic field model with central value of few $mu$G. The logrank statistical test indicates that there are no differences in the depolarization trend observed in cluster with and without radio halo, while the same test indicates significant differences when the depolarization trend of sources in clusters with and without cool core are compared. The comparison between clusters with high and low temperatures does not yields significant differences. Although therole of the gas density should be better accounted for, these results give important indications for models that require a role of the ICM magnetic field to explain the presence of cool core and radio halos in galaxy clusters.
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.
The goal of this work is to put constraints on the strength and structure of the magnetic field in the cluster of galaxies A2382. We investigate the relationship between magnetic field and Faraday rotation effects in the cluster, using numerical simu
lations as a reference for the observed polarization properties. For this purpose we present Very Large Array observations at 20 cm and 6 cm of two polarized radio sources embedded in A2382, and we obtained detailed rotation measure images for both of them. We simulated random three-dimensional magnetic field models with different power spectra and thus produced synthetic rotation measure images. By comparing our simulations with the observed polarization properties of the radio sources, we can determine the strength and the power spectrum of intra-cluster magnetic field fluctuations that best reproduce the observations. The data are consistent with a power law magnetic field power spectrum with the Kolmogorov index $n=11/3$, while the outer scale of the magnetic field fluctuations is of the order of 35 kpc. The average magnetic field strength at the cluster center is about 3 $mu$G and decreases in the external region as the square root of the electron gas density. The average magnetic field strength in the central 1 Mpc$^{3}$ is about 1 $mu$G.
