Observations of magnetic fields in intracluster medium

The presence of μG-level magnetic fields associated with the intracluster medium of galaxy clusters is now widely acknowledged. Our knowledge of their properties has greatly improved in the recent years thanks to both new radio observations and the developments of new techniques to interpret data

Mega-parsec scale magnetic fields in low density regions in the SKA era: filaments connecting galaxy clusters and groups

The presence of magnetic fields in galaxy clusters has been well established in recent years, and their importance for the understanding of the physical processes at work in the Intra Cluster Medium has been recognized. Halo and relic sources have been detected in several tens clusters. A strong correlation is present between the halo and relic radio power and the X-ray luminosity. Since cluster X-Ray luminosity and mass are related, the correlation between the radio power and X-ray luminosity could derive from a physical dependence of the radio power on the cluster mass, therefore the cluster mass could be a crucial parameter in the formation of these sources. The goal of this project is to investigate the existence of non-thermal structures beyond the Mpc scale, and associated with lower density regions with respect to clusters of galaxies: galaxy filaments connecting rich clusters. We present a piece of evidence of diffuse radio emission in intergalactic filaments. Moreover, we present and discuss the detection of radio emission in galaxy groups and in faint X-Ray clusters, to analyze non-thermal properties in low density regions with physical conditions similar to galaxy filaments. We discuss how SKA1 observations will allow the investigation of this topic and the study of the presence of diffuse radio sources in low density regions. This will be a fundamental step to understand the origin and properties of cosmological magnetic fields.Comment: 9 pages, 5 figures - to appear as part of 'Cosmic Magnetism' in Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14)10

A Strong Merger Shock in Abell 665

Deep (103 ks) \chandra\ observations of Abell 665 have revealed rich structures in this merging galaxy cluster, including a strong shock and two cold fronts. The newly discovered shock has a Mach number of $M$ = 3.0 $\pm$ 0.6, propagating in front of a cold disrupted cloud. This makes Abell~665 the second cluster where a strong merger shock of $M \approx$ 3 has been detected, after the Bullet cluster. The shock velocity from jump conditions is consistent with (2.7 $\pm$ 0.7) $\times$ 10$^3$ km sec$^{-1}$. The new data also reveal a prominent southern cold front, with potentially heated gas ahead of it. Abell 665 also hosts a giant radio halo. There is a hint of diffuse radio emission extending to the shock at the north, which needs to be examined with better radio data. This new strong shock provides a great opportunity to study the re-acceleration model with the X-ray and radio data combined.Comment: Accepted for publication in ApJ

Comparisons of Cosmological MHD Galaxy Cluster Simulations to Radio Observations

Radio observations of galaxy clusters show that there are $\mu$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 $|RM|$ and the dispersion of RM ($\sigma_{RM}$), are consistent at a first-order with the radial distribution from observations. The correlations between the $\sigma_{RM}$ 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

The study of extended emission in a radio galaxy detected in the LOFAR Two-Metre Sky Survey

We performed a search for extended radio sources in the Low-Frequency Array Two-Meter Survey HETDEX Spring Field, and we were able to identify 11 low-brightness extended sources. In this paper we focus on the poorly studied radio galaxy PGC2285791, presenting a detailed analysis of its core, its two extended radio lobes, a spectral index map between 141 and 1400 MHz, and the multifrequency association with its IR and optical counterparts. Our results led to the identification of this source with a z = 0.14 extended radio galaxy exhibiting bubble-like radio lobe structures (∼6 arcmin in the S-N direction)

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