arXiv subjects

K. Otmianowska-Mazur

Publications and source records attributed to K. Otmianowska-Mazur.

24 records · Page 2Linked to original sources

arXiv2004

Amplification of Galactic Magnetic Fields by the Cosmic-Ray Driven Dynamo

We present the first numerical model of the magnetohydrodynamical cosmic-ray (CR) driven dynamo of the type proposed by Parker (1992). The driving force of the amplification process comes from CRs injected into the galactic disk in randomly distributed spherical regions representing supernova remnants. The underlying disk is differentially rotating. An explicit resistivity is responsible for the dissipation of the small-scale magnetic field component. We obtain amplification of the large-scale magnetic on a timescale 250 Myr.

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arXiv2003

Magnetic field evolution in galaxies interacting with the intracluster medium. 3D numerical simulations

A fully three-dimensional (3D) magnetohydrodynamical (MHD) model is applied to simulate the evolution of the large-scale magnetic field in cluster galaxies interacting with the intra-cluster medium (ICM). As the model input we use a time dependent gas velocity field resulting from 3D N-body sticky-particle simulations of a galaxy. The modeled clouds are affected by the ram pressure due to their rapid motion through the ICM in the central part of a cluster. Numerical simulations have shown that after the initial compression phase due to ram pressure a process of gas re-accretion onto the galactic disk takes place. We find that the gas re-accretion leads to an increase of the total magnetic energy without any dynamo action. The simulated magnetic fields are used to construct the model maps of high-frequency (Faraday rotation-free) polarized radio emission. We show that the evolution of the polarized intensity shows features that are characteristic for different evolutionary stages of an ICM-ISM interaction. The comparison of polarized radio continuum emission maps with our model permits to determine whether the galaxy is in the compression or in the re-accretion phase. It also provides an important constraint upon the dynamical modeling of an ICM-ISM interactions.

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arXiv2002

Magnetic fields and radio polarization of barred galaxies - 3D dynamo simulations

A three-dimensional (3D) MHD model is applied to simulate the evolution of a large-scale magnetic field in a barred galaxy possessing a gaseous halo extending to about 2.8 kpc above the galactic plane. As the model input we use a time-dependent velocity field of molecular gas resulting from self-consistent 3D N-body simulations of a galactic disk. We assume that the gaseous halo rotates differentially co-rotating with the disk or decreasing its velocity in the Z direction. The dynamo process included in the model yields the amplification of the magnetic field as well as the formation of field structures high above the galactic disk. The simulated magnetic fields are used to construct the models of a high-frequency (Faraday rotation-free) polarized radio emission that accounts for effects of projection and limited resolution, and is thus suitable for direct comparison with observations. We found that the resultant magnetic field correctly reproduces the observed structures of polarization B-vectors, forming coherent patterns well aligned with spiral arms and with the bar. The process initializing a wave-like behavior of the magnetic field, which efficiently forms magnetic maxima between the spiral arms, is demonstrated. The inclusion of the galactic halo constitutes a step towards a realistic model of galactic magnetic fields that includes as many dynamical components as needed for a realistic description.

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arXiv1998

Global three-dimensional simulations of magnetic field evolution in a galactic disk. II. Gas rich galaxies

A fully three-dimensional computation of induction processes in a disk is performed to investigate the evolution of a large-scale magnetic field in gas-rich barred and spiral galaxies in the presence of field diffusion. As input parameters we use time dependent velocity fields obtained from self-consistent 3D N-body calculations of galactic dynamics. Our present work primarily analyzes the influence of the gas flows in non-axisymmetric gravitational disturbances (like spiral arms and bars) on the behavior of the magnetic field. The magnetic field is found to evolve towards structures resembling dynamical spiral arms and bars, however its distribution is often much more complicated than the velocity field itself. We show that a random configuration of seed magnetic fields quickly dissipates, and is therefore unable to explain the magnetic field strength observed in nearby galaxies. The detailed comparison between the simulated velocity and magnetic fields allows us to establish that the reversals of magnetic vectors appear in the vicinity of the corotation radius of non-axisymmetric disk structures, where the velocity field shows rather abrupt changes. We argue that this explains the observed field reversals in our Galaxy.

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arXiv1997

Global three-dimensional simulations of magnetic field evolution in a galactic disk

The evolution of three-dimensional, large-scale, magnetic fields, in a galactic disk is investigated numerically. The N-body simulations of galactic dynamics are incorporated into the kinematic calculations of induction equations to study the influence of non-axisymmetric gas flows on the galactic magnetic field. The time-dependent gas velocity fields are introduced as input parameters for the MHD-simulations. Our principal concern is to check how dynamical evolution of the galactic gas affects the global magnetic field structure and intensity. We have found that the magnetic field responds sensitively to changes in the gas velocity field, and even slight variations of the dynamical parameters, such as the gas mass/total mass ratio results in nonuniform intensity structures, i.e. magnetic arms. The magnetic lines of force are well aligned with spiral arms and bar due to compressional flows in these features. In the inter-arm regions the areas with magnetic vectors going opposite to the main magnetic spirals are present.

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arXiv1995

Numerical simulation of large-scale magnetic-field evolution in spiral galaxies

The evolution of large-scale magnetic fields in disk galaxies is investigated numerically. The gasdynamical simulations in a disk perturbed by spiral or bar potential are incorporated into the kinematic calculations of induction equations to elucidate the effects of non-axisymmetric disk structure on magnetic fields. The effects of interstellar turbulence are given as the turbulent diffusion of magnetic fields. The usually adopted dynamo mechanism of alpha-effect is not considered in our computations, because it is not obvious about the actual existence of the effect in a galaxy. Our principal concern is to clear how observationally and theoretically well-established gas flow affects the magnetic-field structure and evolution, without putting a lot of artificial parameters in the model. We have found that the density-wave streaming motion of gas has a significant influence on the distribution of magnetic fields: the lines of force are well aligned with spiral arms due to the compressional and additional shearing flow of gas in these regions.

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