Particle module of Piernik MHD code

Piernik is a multi-fluid grid magnetohydrodynamic (MHD) code based on the Relaxing Total Variation Diminishing (RTVD) conservative scheme. The original code has been extended by addition of dust described within the particle approximation. The dust is now described as a system of interacting particles. The particles can interact with gas, which is described as a fluid. The comparison between the test problem results and the results coming from fluid simulations made with Piernik code shows the most important differences between fluid and particle approximations used to describe dynamical evolution of dust under astrophysical conditions.Comment: 4 pages, submitted to the Proceedings of the 17'th Young Scientists' Conference on Astronomy and Space Physics (April 26 - May 1, 2010 Kyiv, Ukraine

Comparison between particle and fluid approximations to dust dynamics

We present a new particle module of the magnetohydrodynamic (MHD) Piernik code. The original multi-fluid grid code based on the Relaxing Total Variation Diminishing (RTVD) scheme has been extended by addition of dust described within the particle approximation. The dust is now described as a system of interacting particles. The particles can interact with gas, which is described as a fluid. In this poster we introduce the scheme used to solve equations of motion for the particles and present the first results coming from the module. The results of test problems are also compared with the results coming from fluid simulations made with Piernik-MHD code. The comparison shows the most important differences between fluid and particle approximations used to describe dynamical evolution of dust under astrophysical conditions.Comment: 2 pages, submitted to the Proceedings of the International Conference of Young Astronomers (September 7-13, 2009 Krak\'ow, Poland

Global galactic dynamo driven by cosmic-rays and exploding magnetized stars

We report first results of first global galactic-scale CR-MHD simulations of cosmic-ray-driven dynamo. We investigate the dynamics of magnetized interstellar medium (ISM), which is dynamically coupled with the cosmic-ray (CR) gas. 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. We conduct numerical simulations with the aid of a new parallel MHD code PIERNIK. We find that the initial magnetization of galactic disks by exploding magnetized stars forms a favourable conditions for the cosmic-ray-driven dynamo. 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. The resulting magnetic field structure in an evolved galaxy appears spiral in the face-on view and reveals the so called X-shaped structure in the edge-on view.Comment: 11 pages, 4 figure

Cosmic-ray driven dynamo in the medium of irregular galaxy

We investigate the cosmic ray driven dynamo in the interstellar medium of irregular galaxy. The observations (Chyzy 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.Comment: 2 pages, 2 figures, To be published in "Cosmic Magnetic Fields: From Planets, to Stars and Galaxies", K.G. Strassmeier, A.G. Kosovichev & J.E. Beckman, eds., Proc. IAU Symp. 259, CU

Cosmic ray driven dynamo in galactic disks. A parameter study

We present a parameter study of the magnetohydrodynamical dynamo driven by cosmic rays in the interstellar medium (ISM) focusing on the efficiency of magnetic field amplification and the issue of energy equipartition between magnetic, kinetic and cosmic ray (CR) energies. We perform numerical CR-MHD simulations of the ISM using the extended version of ZEUS-3D code in the shearing box approximation and taking into account the presence of Ohmic resistivity, tidal forces and vertical disk gravity. CRs are supplied in randomly distributed supernova (SN) remnants and are described by the diffusion-advection equation, which incorporates an anisotropic diffusion tensor. The azimuthal magnetic flux and total magnetic energy are amplified depending on a particular choice of model parameters. We find that the most favorable conditions for magnetic field amplification correspond to magnetic diffusivity of the order of 3\times 10^{25} \cm^2\s^{-1}, SN rates close to those observed in the Milky Way, periodic SN activity corresponding to spiral arms, and highly anisotropic and field-aligned CR diffusion. The rate of magnetic field amplification is relatively insensitive to the magnitude of SN rates in a rage of spanning 10% up to 100% of realistic values. The timescale of magnetic field amplification in the most favorable conditions is 150 Myr, at galactocentric radius equal to 5 kpc. The final magnetic field energies fluctuate near equipartition with the gas kinetic energy. In all models CR energy exceeds the equipartition values by a least an order of magnitude, in contrary to the expected equipartition. We suggest that the excess of cosmic rays can be attributed to the fact that the shearing-box does not permit cosmic rays to leave the system along the horizontal magnetic field.Comment: 12 papges, 11 figures, accepted for publication in Astronomy and Astrophysic

Cosmic-ray driven dynamo in galactic disks

We present new developments on the Cosmic--Ray driven, galactic dynamo, modeled by means of direct, resistive CR--MHD simulations, performed with ZEUS and PIERNIK codes. The dynamo action, leading to the amplification of large--scale galactic magnetic fields on galactic rotation timescales, appears as a result of galactic differential rotation, buoyancy of the cosmic ray component and resistive dissipation of small--scale turbulent magnetic fields. Our new results include demonstration of the global--galactic dynamo action driven by Cosmic Rays supplied in supernova remnants. An essential outcome of the new series of global galactic dynamo models is the equipartition of the gas turbulent energy with magnetic field energy and cosmic ray energy, in saturated states of the dynamo on large galactic scales.Comment: 6 pages, 3 figures, To be published in "Cosmic Magnetic Fields: From Planets, to Stars and Galaxies", K.G. Strassmeier, A.G. Kosovichev & J.E. Beckman, eds., Proc. IAU Symp. 259, CU

Stability of hydrodynamical relativistic planar jets. I. Linear evolution and saturation of Kelvin-Helmholtz modes

The effects of relativistic dynamics and thermodynamics in the development of Kelvin-Helmholtz instabilities in planar, relativistic jets along the early phases (namely linear and saturation phases) of evolution has been studied by a combination of linear stability analysis and high-resolution numerical simulations for the most unstable first reflection modes in the temporal approach. Three different values of the jet Lorentz factor (5, 10 and 20) and a few different values of specific internal energy of the jet matter (from 0.08 to $60.0 c^2$) have been considered. Figures illustrating the evolution of the perturbations are also shown

Can the cosmic-ray driven dynamo model explain the observations of the polarized emission of edge-on galaxies ?

In the present paper we construct maps of polarized synchrotron radio emission of a whole galaxy, based on local models of the cosmic ray (CR) driven dynamo. We perform numerical simulations of the dynamo in local Cartesian domains, with shear-periodic boundary conditions, placed at the different galactocentric radii. Those local solutions are concatenated together to construct the synchrotron images of the whole galaxy. The main aim of the paper is to compare the model results with the observed radio continuum emission from nearly edge-on spiral galaxy. On the basis of the modeled evolution of the magnetic field structure, the polarization maps can be calculated at different time-steps and at any orientation of the modeled galaxy. For the first time a self-consistent cosmic-ray electron distribution is used to integrate synchrotron emissivity along the line of sight. Finally, our maps are convolved with the given radiotelescope beam. We show that it is possible to reconstruct the extended magnetic halo structures of the edge-on galaxies (so called X-shaped structures).Comment: 7 pages, 7 figures. ApJ, accepte