3D numerical simulations of magnetic field evolution in barred galaxies and in spiral galaxies under influence of tidal forces

AbstractWe present the results of the three-dimensional, fully non-linear MHD simulations of the large-scale magnetic field evolution in a barred galaxy with the back reaction of magnetic field to gas. We also include the process of the cosmic-ray driven dynamo. In addition, we check what physical processes are responsible for the magnetic field evolution in the tidally influenced spiral galaxies. We solve the MHD equations for the gas and magnetic field in a spiral galaxy with gravitationally prescribed bulge, disk and halo which travels along common orbit with the second body. In order to compare our modeling results with the observations we also construct the maps of high-frequency (Faraday rotation-free) polarized radio emission from the simulated magnetic fields. The model accounts for the effects of projection and limited resolution.We found 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. We also found a physical explanation of the problem of inconsistency between the velocity and magnetic fields character present in this type of galaxies. 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. The modeled total energy of magnetic field and magnetic flux grows exponentially due to the action of the cosmic-ray driven dynamo. We also obtained the polarization maps of tidally influenced spiral galaxies which are similar to observations.

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Magnetic Fields and Halos in Spiral Galaxies

Galaxies ◽

10.3390/galaxies7020054 ◽

2019 ◽

Vol 7 (2) ◽

pp. 54 ◽

Cited By ~ 4

Author(s):

Marita Krause

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Spiral Galaxies ◽

Cosmic Ray ◽

Radio Continuum ◽

Field Pattern ◽

Dynamo Action ◽

Disk Plane ◽

The Magnetic Field

Radio continuum and polarization observations reveal best the magnetic field structure and strength in nearby spiral galaxies. They show a similar magnetic field pattern, which is of spiral shape along the disk plane and X-shaped in the halo, sometimes accompanied by strong vertical fields above and below the central region of the disk. The strength of the total halo field is comparable to that of the disk. The small- and large-scale dynamo action is discussed to explain the observations with special emphasis on the rôle of star formation on the α − Ω dynamo and the magnetic field strength and structure in the disk and halo. Recently, with RM-synthesis of the CHANG-ES observations, we obtained the first observational evidence for the existence of regular magnetic fields in the halo. The analysis of the radio scale heights indicate escape-dominated radio halos with convective cosmic ray propagation for many galaxies. These galactic winds may be essential for an effective dynamo action and may transport large-scale magnetic field from the disk into the halo.

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CHANG-ES

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834515 ◽

2019 ◽

Vol 623 ◽

pp. A33 ◽

Cited By ~ 14

Author(s):

Y. Stein ◽

R.-J. Dettmar ◽

J. Irwin ◽

R. Beck ◽

M. Weżgowiec ◽

...

Keyword(s):

Magnetic Field ◽

Cosmic Rays ◽

Magnetic Fields ◽

Large Scale ◽

Spiral Galaxies ◽

Cosmic Ray ◽

Transport Processes ◽

X Ray ◽

Radio Data ◽

The Magnetic Field

Context. The observation of total and linearly polarized synchrotron radiation of spiral galaxies in the radio continuum reveals the distribution and structure of their magnetic fields. By observing these, information about the proposed dynamo processes that preserve the large-scale magnetic fields in spiral galaxies can be gained. Additionally, by analyzing the synchrotron intensity, the transport processes of cosmic rays into the halo of edge-on spiral galaxies can be investigated. Aims. We analyze the magnetic field geometry and the transport processes of the cosmic rays of the edge-on spiral starburst galaxy NGC 4666 from CHANG-ES radio data in two frequencies; 6 GHz (C-band) and 1.5 GHz (L-band). Supplementary X-ray data are used to investigate the hot gas in NGC 4666. Methods. We determine the radio scale heights of total power emission at both frequencies for this galaxy. We show the magnetic field orientations derived from the polarization data. Using rotation measure (RM) synthesis we further study the behavior of the RM values along the disk in C-band to investigate the large-scale magnetic-field pattern. We use the revised equipartition formula to calculate a map of the magnetic field strength. Furthermore, we model the processes of cosmic-ray transport into the halo with the 1D SPINNAKER model. Results. The extended radio halo of NGC 4666 is box-shaped and is probably produced by the previously observed supernova-driven superwind. This is supported by our finding of an advective cosmic-ray transport such as that expected for a galactic wind. The scale-height analysis revealed an asymmetric halo above and below the disk as well as between the two sides of the major axis. A central point source as well as a bubble structure is seen in the radio data for the first time. Our X-ray data show a box-shaped hot halo around NGC 4666 and furthermore confirm the AGN nature of the central source. NGC 4666 has a large-scale X-shaped magnetic field in the halo, as has been observed in other edge-on galaxies. The analysis furthermore revealed that the disk of NGC 4666 shows hints of field reversals along its radius, which is the first detection of this phenomenon in an external galaxy.

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Dynamo in Astrophysics

Symposium - International Astronomical Union ◽

10.1017/s0074180900189636 ◽

1990 ◽

Vol 140 ◽

pp. 83-89

Author(s):

A.A. Ruzmaikin

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Turbulent Flow ◽

Large Scale ◽

Spiral Galaxies ◽

Clusters Of Galaxies ◽

Magnetic Structures ◽

Random Magnetic Field ◽

Astrophysical Objects

The fast dynamo acting in a turbulent flow explains the origin of magnetic fields in astrophysical objects. Stellar cycles and large-scale magnetic fields in spiral galaxies reflect the behaviour of a mean magnetic field. Intermittent magnetic structures in clusters of galaxies are associated with random magnetic field.

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Magnetic field evolution in dwarf and Magellanic-type galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201730566 ◽

2018 ◽

Vol 611 ◽

pp. A7 ◽

Cited By ~ 1

Author(s):

H. Siejkowski ◽

M. Soida ◽

K. T. Chyży

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Large Scale ◽

Magnetic Energy ◽

Galactic Disk ◽

Cosmic Ray ◽

Dark Matter Halo ◽

Field Evolution ◽

Low Mass ◽

The Magnetic Field

Aims. Low-mass galaxies radio observations show in many cases surprisingly high levels of magnetic field. The mass and kinematics of such objects do not favour the development of effective large-scale dynamo action. We attempted to check if the cosmic-ray-driven dynamo can be responsible for measured magnetization in this class of poorly investigated objects. We investigated how starburst events on the whole, as well as when part of the galactic disk, influence the magnetic field evolution. Methods. We created a model of a dwarf/Magellanic-type galaxy described by gravitational potential constituted from two components: the stars and the dark-matter halo. The model is evolved by solving a three-dimensional (3D) magnetohydrodynamic equation with an additional cosmic-ray component, which is approximated as a fluid. The turbulence is generated in the system via supernova explosions manifested by the injection of cosmic-rays. Results. The cosmic-ray-driven dynamo works efficiently enough to amplify the magnetic field even in low-mass dwarf/Magellanic-type galaxies. The e-folding times of magnetic energy growth are 0.50 and 0.25 Gyr for the slow (50 km s−1) and fast (100 km s−1) rotators, respectively. The amplification is being suppressed as the system reaches the equipartition level between kinetic, magnetic, and cosmic-ray energies. An episode of star formation burst amplifies the magnetic field but only for a short time while increased star formation activity holds. We find that a substantial amount of gas is expelled from the galactic disk, and that the starburst events increase the efficiency of this process.

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3D model of magnetic fields evolution in dwarf irregular galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311007344 ◽

2010 ◽

Vol 6 (S274) ◽

pp. 389-392

Author(s):

Hubert Siejkowski ◽

Marian Soida ◽

Katarzyna Otmianowska-Mazur ◽

Michał Hanasz ◽

Dominik J. Bomans

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Gravitational Potential ◽

Spiral Galaxies ◽

Cosmic Ray ◽

Dynamo Model ◽

Slow Rotation ◽

Irregular Galaxies ◽

Dwarf Irregular Galaxies ◽

The Magnetic Field

AbstractRadio observations show that magnetic fields are present in dwarf irregular galaxies (dIrr) and its strength is comparable to that found in spiral galaxies. Slow rotation, weak shear and shallow gravitational potential are the main features of a typical dIrr galaxy. These conditions of the interstellar medium in a dIrr galaxy seem to unfavourable for amplification of the magnetic field through the dynamo process. Cosmic-ray driven dynamo is one of the galactic dynamo model, which has been successfully tested in case of the spiral galaxies. We investigate this dynamo model in the ISM of a dIrr galaxy. We study its efficiency under the influence of slow rotation, weak shear and shallow gravitational potential. Additionally, the exploding supernovae are parametrised by the frequency of star formation and its modulation, to reproduce bursts and quiescent phases. We found that even slow galactic rotation with a low shearing rate amplifies the magnetic field, and that rapid rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.

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Interstellar and intergalactic dynamos

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313002573 ◽

2012 ◽

Vol 8 (S294) ◽

pp. 225-236

Author(s):

M. Hanasz ◽

D. Woltanski ◽

K. Kowalik

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Numerical Models ◽

Rotation Period ◽

Cosmic Ray ◽

Small Scale ◽

Galactic Rotation ◽

Galaxy Mergers ◽

Wide Range

AbstractWe review recent developments of amplification models of galactic and intergalactic magnetic field. The most popular scenarios involve variety of physical mechanisms, including turbulence generation on a wide range of physical scales, effects of supernovae, buoyancy as well as the magnetorotational instability. Other models rely on galaxy interaction, which generate galactic and intergalactic magnetic fields during galaxy mergers. We present also global galactic-scale numerical models of the Cosmic Ray (CR) driven dynamo, which was originally proposed by Parker (1992). We conduct a series of direct CR+MHD numerical simulations of the dynamics of the interstellar medium (ISM), composed of gas, magnetic fields and CR components. We take into account CRs accelerated in randomly distributed supernova (SN) remnants, and assume that SNe deposit small-scale, randomly oriented, dipolar magnetic fields into the ISM. The amplification timescale of the large-scale magnetic field resulting from the CR-driven dynamo is comparable to the galactic rotation period. The process efficiently converts small-scale magnetic fields of SN-remnants into galactic-scale magnetic fields. The resulting magnetic field structure resembles the X-shaped magnetic fields observed in edge-on galaxies.

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Spin-Down of Solar-Type Stars with Internal Magnetic Fields

International Astronomical Union Colloquium ◽

10.1017/s0252921100018261 ◽

1993 ◽

Vol 137 ◽

pp. 464-468

Author(s):

Paul Charbonneau ◽

Keith B. Macgregor

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Differential Rotation ◽

Large Scale ◽

Back Reaction ◽

Large Set ◽

Large Scale Magnetic Field ◽

Solar Type ◽

Solar Type Star ◽

Selection Of

AbstractWe present a selection of results from a large set of numerical simulations of the spin-down of a solar-type star containing a large scale magnetic field in its radiative interior. Our computations are dynamical, in that they take into account both the generation of the toroidal component by the wind-induced shear endits back-reaction on the azimuthal flow. Our results demonstrate the existence of classes of internal magnetic fields that can accomodate rapid spin-down near the ZAMS, and yield weak internal differential rotation by the solar age.

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GLOBAL SIMULATIONS OF THE MAGNETIC FIELD EVOLUTION IN BARRED GALAXIES UNDER THE INFLUENCE OF THE COSMIC-RAY-DRIVEN DYNAMO

The Astrophysical Journal ◽

10.1088/2041-8205/733/2/l18 ◽

2011 ◽

Vol 733 (2) ◽

pp. L18 ◽

Cited By ~ 33

Author(s):

K. Kulpa-Dybeł ◽

K. Otmianowska-Mazur ◽

B. Kulesza-Żydzik ◽

M. Hanasz ◽

G. Kowal ◽

...

Keyword(s):

Magnetic Field ◽

Cosmic Ray ◽

Barred Galaxies ◽

Field Evolution ◽

The Magnetic Field

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On the combined role of cosmic rays and supernova-driven turbulence for galactic dynamos

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3509 ◽

2020 ◽

Vol 500 (3) ◽

pp. 3527-3535

Author(s):

Abhijit B Bendre ◽

Detlef Elstner ◽

Oliver Gressel

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Mean Field ◽

Cosmic Ray ◽

Field Method ◽

Dynamo Model ◽

Test Field ◽

Dynamo Action ◽

Magnetohydrodynamic Simulations

ABSTRACT Large-scale coherent magnetic fields observed in the nearby galaxies are thought to originate by a mean-field dynamo. This is governed via the turbulent electromotive force (EMF, $\overline{{\boldsymbol {\cal E}} {}}$) generated by the helical turbulence driven by supernova (SN) explosions in the differentially rotating interstellar medium (ISM). In this paper, we aim to investigate the possibility of dynamo action by the virtue of buoyancy due to a cosmic ray (CR) component injected through the SN explosions. We do this by analysing the magnetohydrodynamic simulations of local shearing box of ISM in which the turbulence is driven via random SN explosions and the energy of the explosion is distributed in the CR and/or thermal energy components. We use the magnetic field aligned diffusion prescription for the propagation of CR. We compare the evolution of magnetic fields in the models with the CR component to our previous models that did not involve the CR. We demonstrate that the inclusion of CR component enhances the growth of dynamo slightly. We further compute the underlying dynamo coefficients using the test-field method and argue that the entire evolution of the large-scale mean magnetic field can be reproduced with an α − Ω dynamo model. We also show that the inclusion of CR component leads to an unbalanced turbulent pumping between magnetic field components and additional dynamo action by the Rädler effect.

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Cosmic-ray driven dynamo in galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311007265 ◽

2010 ◽

Vol 6 (S274) ◽

pp. 355-360 ◽

Cited By ~ 1

Author(s):

M. Hanasz ◽

D. Wóltanski ◽

K. Kowalik ◽

H. Kotarba

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Numerical Models ◽

Rotation Period ◽

Cosmic Ray ◽

Small Scale ◽

Galactic Rotation ◽

Large Scale Magnetic Field ◽

Recent Developments

AbstractWe present recent developments of global galactic-scale numerical models of the Cosmic Ray (CR) driven dynamo, which was originally proposed by Parker (1992). We conduct a series of direct CR+MHD numerical simulations of the dynamics of the interstellar medium (ISM), composed of gas, magnetic fields and CR components. We take into account CRs accelerated in randomly distributed supernova (SN) remnants, and assume that SNe deposit small-scale, randomly oriented, dipolar magnetic fields into the ISM. The amplification timescale of the large-scale magnetic field resulting from the CR-driven dynamo is comparable to the galactic rotation period. The process efficiently converts small-scale magnetic fields of SN-remnants into galactic-scale magnetic fields. The resulting magnetic field structure resembles the X-shaped magnetic fields observed in edge-on galaxies.

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