We conduct global galactic–scale magnetohydrodynamical (MHD) simulations of the cosmic–ray driven dynamo. We assume that exploding stars deposit small–scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of cosmic rays, accelerated in supernova shocks. Our simulations are performed with the aid of a new parallel MHD code PIERNIK. We demonstrate that dipolar magnetic fields supplied on small SN–remnant scales, can be amplified exponentially by the CR–driven dynamo to the present equipartition values, and transformed simultaneously to large galactic–scales by an inverse cascade promoted by resistive processes.

We present a set of global, self-consistent N-body/SPH simulations of the dynamic evolution of galactic discs with gas and including magnetic fields. We have implemented a description to follow the ideal induction equation in the SPH part of the code Vine. Results from a direct implementation of the field equations are compared to a representation by Euler potentials, which pose a ∇ ċ B-free description, a constraint not fulfilled for the direct implementation. All simulations are compared to an implementation of magnetic fields in the code Gadget. Starting with a homogeneous field we find a tight connection of the magnetic field structure to the density pattern of the galaxy in our simulations, with the magnetic field lines being aligned with the developing spiral pattern of the gas. Our simulations clearly show the importance of non-axisymmetry of the dynamic pattern for the evolution of the magnetic field.

We present results of three-dimensional, fully nonlinear MHD simulations of a large-scale magnetic field evolution in a barred galaxy. The model does not take into consideration the dynamo process. We find that the obtained magnetic field configurations are highly similar to the observed maps of the polarized intensity of barred galaxies, because the modeled vectors form coherent structures along the bar and spiral arms. Due to the dynamical influence of the bar the gas forms spiral waves which go radially outward. Each spiral arm forms the magnetic arm which stays much longer in the disk, than the gaseous spiral structure. Additionally the modeled total energy of magnetic field grows due to strong compression and shear of non-axisymmetrical bar flows and differential rotation, respectively.

The low masses of irregular galaxies change the behavior of their interstellar medium (ISM) compared to that of normal spirals, so the role of magnetic fields in the ISM in irregulars may be very different than in spirals. We present high-resolution and high-sensitivity observations of the magnetic fields of two irregular galaxies: NGC 4214 and NGC 1569.

We investigate the cosmic ray driven dynamo in the interstellar medium of irregular galaxy. The observations (Chyży et al. 2000, 2003) show that the magnetic field in irregular galaxies is present and its value reaches the same level as in spiral galaxies. However the conditions in the medium of irregular galaxy are very unfavorable for amplification the magnetic field due to slow rotation and low shearing rate.

In this work we present numerical model of the interstellar medium in irregular galaxies. The model includes magnetohydrodynamical dynamo driven by cosmic rays in the interstellar medium provided by random supernova explosions. We describe models characterized by different shear and rotation. We find that even slow galactic rotation with low shearing rate gives amplification of the magnetic field. Simulations have shown that high amount of the magnetic energy flow out off the simulation region becoming an efficient source of intergalactic magnetic fields.

The Dominion Radio Astrophysical Observatory synthesis telescope (DRAO-ST) was used to produce a deep polarization mosaic at 1.4 GHz to a noise level of 45 microJy beam−1 for both Stokes Q and U at 1′ resolution. The DRAO deep field covers 8.6 sq. degrees in polarization centered on the ELAIS N1 field. We identified over 1700 total intensity (Stokes I) radio sources of which 197 are linearly polarized down to a flux density level of 203 microJy. The fractional polarization of faint polarized sources are flat down to a polarized flux density of about 4 mJy, at which point the numbers increase, until the counts drop for polarized flux densities below 1 mJy. These faint polarized radio sources are mostly AGNs with luminosities below the traditional FRI/FRII boundary. Follow-up observations with the VLA show that the origin of the polarization of the radio sources down to a polarized flux of 1 mJy comes from both the lobes and central region of these objects.

We report multi-frequency circular polarization measurements for the radio source 0056-00 taken at the Effelsberg 100-m radio telescope. The data reduction is based on a new calibration procedure that allows the contemporary measurement of the four Stokes parameters with single-dish radio telescopes.

In this work, we present 3D MHD simulations of non-helical, forced turbulence, with an anisotropic thermal pressure with respect to the orientation of the local magnetic field. Such anisotropy arises when the plasma is weakly collisional, i.e., when the Larmor frequency is much greater than the ion-ion collision frequency. In this Kinetic MHD regime (KMHD), there are instabilities that give rise to fast growing magnetic fluctuations in the smallest scales. The plasma that fills the intergalactic and intracluster media has small density (n ~ 10−3cm−3), hence the effects of these instabilities could be important in the turbulent amplification of the magnetic fields there. In order to study the KMHD turbulence, we have performed 3D numerical simulations employing a godunov-MHD code (e.g., Kowal, Lazarian & Beresnyak 2007; Falceta-Gonçalves, Lazarian & Kowal 2008). The power spectrum of the velocity and magnetic fields were calculated for two cases: when there is a pre-existing mean magnetic field, and when there is only an initial weak magnetic field.

Using Smoothed Particle Magneto Hydrodynamics (Dolag & Stasyszyn), we study the effects of magnetic fields in galaxy clusters with the aim to infer their dynamical role within the cool core region. Therefore we we investigate the role of regularization as well as divergence cleaning schemes (Stasyszyn & Dolag 2009). We run cosmological simulations of a reference cluster in order to evaluate our various implementation in a realistic scenario. The preliminary results indicate that the final magnetic field profile in the simulations depends only on the amount of artificial dissipation, but not in the amount of numerical div(B) present in the different implementation. We also present first results from simulations which are including radiative cooling and star formation. Even at the this low resolution we find a strong additional amplification of the magnetic field within the cool core region indicating that magnetic pressure could become comparable to the thermal pressure in theses regimes.

The Perseus Cluster (A426) is the brightest cluster of galaxies observed in X-rays in the sky and its giant central galaxy (NGC1275) hosts the extended double radio source 3C84. There is a spectacular H-alpha nebulosity surrounding NGC1275 with loops and filaments that are probably magnetized and extend over 100 kpc. The continuous blowing of bubbles leading to the propagation of shock fronts is also evident and more recently, outflow and infall velocities of several 1000 km/s have been detected associated to the surrounding filaments. We here present preliminary results of 2.5D MHD simulations of the Perseus cluster central region assuming that the production of the outflow structures and loops that arise from the surface of NGC1275 are due to turbulent injection triggered by recent star formation and SNe activity in the galaxy. This is in turn, probably induced by a continuous gas infall from the satellite galaxies around NGC1275. Our simulations which include both, the turbulent gas outflow and gas infall from the surroundings, have revealed a continuous formation of the observed features, like the filaments, the gigantic magnetic loops and weak shock fronts that propagate into the ICM medium with the observed velocities of 1000–5000 km/s. After 10 Myr, a nearly steady state is established between the outflow material emerging from the central galaxy and the inflow gas from the surrounds. The outflow activity seems to retard the cannibalism action of the central galaxy over the surrounding galaxies. This result may have important implications over the evolution of the whole cluster as it seems to indicate that the SF and SNe production that are induced by the cannibalism may help to decelerate the later due to turbulence and outflow production. These results also offer important clues to the hot halo formation in the center of the cluster and in the suppression of cooling flows.

The distribution of the Faraday depth induced by galaxies, groups and clusters on a patch of sky is investigated. For instance, we utilise a halo model approach to obtain synthetic Faraday skies. Moreover, our modelling includes cluster physical as well as cosmological aspects. A SKA sky survey will provide a large sample of rotation measures of polarised sources. Hence, we examine to what extent statistics of rotation measures of these sources can yield information about cosmic magnetic fields and cosmology.

We discuss how measurements of linear polarisation of cluster background and embedded sources can be used to study cluster magnetic fields via Faraday rotation. We make forecasts for up-coming radio instruments on the basis of synthetic radio sky observations. Our mock polarised sky is modelled to agree with the sparse available data. By applying Bayesian statistical analysis methods, such as Markov Chain Monte Carlo and nested sampling techniques, we investigate which constraints can be placed on cluster magnetic field properties.

We study the spatial structure of the 3-dimensional large-scale pattern of the Galactic Magnetic Field using the polarization maps obtained by the WMAP satellite at 22 GHz. By using five different models of the large-scale magnetic field of the Milky Way and a model for the cosmic rays distribution, we predict the expected polarized synchrotron emission. Those maps are compared to the observed 22 GHz polarization data using a Maximum Likelihood method. For each model, we obtain the parameter values which better reproduce the data and obtain their marginal probability distribution functions. We find that the model that best reproduces the observed polarization maps is an “axisymmetric” model.

We begin with a brief review of Zeeman-splitting fundamentals and the importance of circular polarization, i.e. Stokes V. We then turn to modern results in several areas, emphasizing the diffuse interstellar medium in the Galaxy. The median field in the Cold Neutral Medium is determined from HI absorption lines and is about 6 μG; the magnetic and turbulent pressures are comparable. Using HI emission lines the field has been mapped in several areas: the field reverses across the Orion Molecular Cloud; the 3-d field structure has been determined in the ρ Oph region; and in regions having shock-like morphology the field is generally stronger, strong enough to limit further compression. We briefly present new field measurements for: photo-dissociation regions at the edges of HII regions, determined from carbon recombination lines; Ultra Luminous Infrared Galaxies, from OH megamasers; and the 3C 286 damped Lyman-α absorption system, determined from the 21-cm line in absorption. We show the sidelobe response of the Green Bank Telescope, which is surprisingly severe and makes the telescope less than optimum for Zeeman-splitting measurements of HI emission lines. Finally, we compare two techniques for determining field strengths, i.e. Zeeman splitting and the Chandrasekhar-Fermi method, and show why the latter usually gives higher field strengths – and sometimes unrealistically high fields.

We discuss practical aspects of the novel Faraday Rotation Measure Synthesis technique, first described by Burn (1966), and recently extended and implemented by Brentjens & de Bruyn (2005). The method takes advantage of the excellent spectral coverage provided by modern radio telescopes to reconstruct the intrinsic polarization properties along a line of sight, using a Fourier relationship between the observed polarization products and a function describing the intrinsic polarization (the Faraday dispersion function). An important consequence of the Fourier relationship and discrete frequency sampling is the need, in some cases, to deconvolve the sampling response from the reconstructed Faraday dispersion function. Practical aspects of the deconvolution procedure are discussed. We illustrate the use of the technique by summarizing a recent investigation carried out with the WSRT. We conclude by briefly describing the applicability to future programs which will be carried out with the next generation of radio telescopes such as LOFAR.

Our position inside the Galaxy requires all-sky surveys to reveal its large-scale properties. The zero-level calibration of all-sky surveys differs from standard ‘relative’ measurements, where a source is measured in respect to its surroundings. All-sky surveys aim to include emission structures of all angular scales exceeding their angular resolution including isotropic emission components. Synchrotron radiation is the dominating emission process in the Galaxy up to frequencies of a few GHz, where numerous ground based surveys of the total intensity up to 1.4 GHz exist. Its polarization properties were just recently mapped for the entire sky at 1.4 GHz. All-sky total intensity and linear polarization maps from WMAP for frequencies of 23 GHz and higher became available and complement existing sky maps. Galactic plane surveys have higher angular resolution using large single-dish or synthesis telescopes. Polarized diffuse emission shows structures with no relation to total intensity emission resulting from Faraday rotation effects in the interstellar medium. The interpretation of these polarization structures critically depends on a correct setting of the absolute zero-level in Stokes U and Q.

Some of the earliest polarimetric measurements made in astronomy were concerned with the polarization of the interstellar medium resulting from dust grains aligned in the Galactic magnetic field. More than 50 years later, polarimetry continues to be an important diagnostic of field structure on size scales ranging from planetary to galactic. The use of both linear and circular polarimetry at optical and infrared wavelengths can provide additional insights into the nature of dust particles, their alignment in magnetic fields and the field topology. Given the science benefits that polarimetry offers it is perhaps surprising that the continued existence of polarimetric facilities on current and next generation large telescopes needs to be ensured.

Polarized light provides the most reliable source of information at our disposal for diagnosing the physical properties of astrophysical plasmas, including the magnetic fields of the solar atmosphere. The interaction between radiation and hydrogen plus free electrons through Rayleigh and Thomson scattering gives rise to the polarization of the stellar continuous spectrum, which is very sensitive to the medium's thermal and density structure. Anisotropic radiative pumping processes induce population imbalances and quantum coherences among the sublevels of degenerate energy levels (that is, atomic level polarization), which produce polarization in spectral lines without the need of a magnetic field. The Hanle effect caused by the presence of relatively weak magnetic fields modifies the atomic polarization of the upper and lower levels of the spectral lines under consideration, allowing us to detect magnetic fields to which the Zeeman effect is blind. After discussing the physical origin of the polarized radiation in stellar atmospheres, this paper highlights some recent developments in polarized radiation diagnostic methods and a few examples of their application in solar physics.

Zeeman-Doppler Imaging (ZDI) is a powerful inversion method to reconstruct stellar magnetic surface fields. The reconstruction process is usually solved by translating the inverse problem into a regularized least-square or optimization problem. In this contribution we will emphasize that ZDI is an inherent non-linear problem and the corresponding regularized optimization is, like many non-linear problems, potentially prone to local minima. We show how this problem will be exacerbated by using an inadequate forward model. To facilitate a more consistent full radiative transfer driven approach to ZDI we describe a two-stage strategy that consist of a principal component analysis (PCA) based line profile reconstruction and a fast approximate polarized radiative transfer method to synthesize local Stokes profiles. Moreover, we introduce a novel statistical inversion method based on artificial neural networks (ANN) which provide a fast calculation of a first guess model and allows to incorporate better physical constraints into the inversion process.

One of the five key science projects for the Square Kilometre Array (SKA) is “The Origin and Evolution of Cosmic Magnetism”, in which radio polarimetry will be used to reveal what cosmic magnets look like and what role they have played in the evolving Universe. Many of the SKA prototypes now being built are also targeting magnetic fields and polarimetry as key science areas. Here I review the prospects for innovative new polarimetry and Faraday rotation experiments with forthcoming facilities such as ASKAP, LOFAR, the ATA, the EVLA, and ultimately the SKA. Sensitive wide-field polarisation surveys with these telescopes will provide a dramatic new view of magnetic fields in the Milky Way, in nearby galaxies and clusters, and in the high-redshift Universe.