Galactic winds and the symmetry properties of galactic magnetic fields

Moss, D.; Sokoloff, Dmitry; Beck, Rainer; Krause, M.

doi:10.1051/0004-6361/200913509

Cited by 57 publications

(76 citation statements)

References 13 publications

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“…This mean value agrees with theoretical predictions (e.g., Wielebinski & Krause 1993;Ferrière & Schmitt 2000;Moss et al 2010) and previous observations (e.g., Mathewson & Ford 1970;Heiles 2000;Men et al 2008). Analysis of NIR starlight polarimetry in the outer (Pavel et al 2012) and inner (Clemens et al 2012a) Galaxy also supports the conclusion that a single mean orientation is a reasonable characterization of the Galactic magnetic field in the disk.…”

Section: Starlight Polarimetry Toward Galactic Bubblessupporting

confidence: 92%

H Ii Region Driven Galactic Bubbles and Their Relationship to the Galactic Magnetic Field

Pavel

Clemens

2012

ApJ

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The relative alignments of mid-infrared traced Galactic bubbles are compared to the orientation of the mean Galactic magnetic field in the disk. The orientations of bubbles in the northern Galactic plane were measured and are consistent with random orientations-no preferential alignment with respect to the Galactic disk was found. A subsample of H ii region driven Galactic bubbles was identified, and as a single population they show random orientations. When this subsample was further divided into subthermal and suprathermal H ii regions, based on hydrogen radio recombination linewidths, the subthermal H ii regions showed a marginal deviation from random orientations, but the suprathermal H ii regions showed significant alignment with the Galactic plane. The mean orientation of the Galactic disk magnetic field was characterized using new near-infrared starlight polarimetry and the suprathermal H ii regions were found to preferentially align with the disk magnetic field. If suprathermal linewidths are associated with younger H ii regions, then the evolution of young H ii regions is significantly affected by the Galactic magnetic field. As H ii regions age, they cease to be strongly linked to the Galactic magnetic field, as surrounding density variations come to dominate their morphological evolution. From the new observations, the ratios of magnetic-to-ram pressures in the expanding ionization fronts were estimated for younger H ii regions.

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Section: Starlight Polarimetry Toward Galactic Bubblessupporting

confidence: 92%

H Ii Region Driven Galactic Bubbles and Their Relationship to the Galactic Magnetic Field

Pavel

Clemens

2012

ApJ

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“…However, model calculations of the mean-field αΩ-dynamo for a disk surrounded by a spherical halo including a galactic wind (Brandenburg et al 1993;and Moss et al 2010) simulated similar field configurations as the observed ones. Meanwhile, new MHD simulations of disk galaxies including a galactic wind are in progress and may explain the X-shaped field (Gressel et al 2008;Hanasz et al 2009a,b).…”

Section: Dynamo Action and Galactic Windmentioning

confidence: 57%

The large scale magnetic field structure of the spiral galaxy NGC 5775

Soida

Krause

Dettmar

et al. 2011

A&A

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Context. The origin of large-scale magnetic fields in spiral galaxies is still a theoretical riddle and better observational constraints are required to make further progress. Aims. In order to better determine the large-scale 3D-structure of magnetic fields in spiral galaxies we present a Faraday rotation analysis of the edge-on spiral galaxy NGC 5775. Methods. Deep radio-continuum observations in total power and linear polarization were performed at 8.46 GHz with the VLA and the 100-m Effelsberg telescope. They were analyzed together with archival 4.86 and 1.49 GHz VLA-data. We thus can derive rotation measures from a comparison of three frequencies and determine the intrinsic magnetic field structure. Results. A very extended halo is detected in NGC 5775, with magnetic field lines forming an X-shaped structure. Close to the galactic disk the magnetic field is plane-parallel. The scaleheights of the radio emission esimated for NGC 5775 are comaprable with other galaxies. The rotation measure distribution varies smoothly on both sides along the major axis from positive to negative values. Conclusions. From the derived distribution of rotation measures and the plane-parallel intrinsic magnetic field orientation along the galactic midplane we conclude that NGC 5775 has an even axisymmetric large-scale magnetic field configuration in the disk as generated by an αΩ-dynamo which is accompanied by a quadrupolar poloidal field. The magnetic field lines of the plane-parallel component are pointing outwards. The observed X-shaped halo magnetic field, however, cannot be explained by the action of the disk's mean-field dynamo alone. It is probably due to the influence of the galactic wind together with the dynamo action.

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“…In the case of S100 model, the toroidal magnetic field component has a different direction above and below the disk plane, which indicates an odd (dipole-type) configuration of magnetic field with respect to the galactic plane. The odd symmetry of the magnetic field is not the preferred configuration in the disk geometry (Moss et al 2010), while it has been found in some galaxies (e.g., in NGC 4631, Krause 2003).…”

Section: Discussionmentioning

confidence: 88%

The effect of supernova rate on the magnetic field evolution in barred galaxies

Kulpa-Dybeł

Nowak

Otmianowska-Mazur

et al. 2015

A&A

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Context. For the first time, our magnetohydrodynamical numerical calculations provide results for a three-dimensional model of barred galaxies involving a cosmic-ray driven dynamo process that depends on star formation rates. Furthermore, we argue that the cosmic-ray driven dynamo can account for a number of magnetic features in barred galaxies, such as magnetic arms observed along the gaseous arms, magnetic arms in the inter-arm regions, polarized emission that is at the strongest in the central part of the galaxy, where the bar is situated, polarized emission that forms ridges coinciding with the dust lanes along the leading edges of the bar, as well as their very strong total radio intensity. Aims. Our numerical model probes what kind of physical processes could be responsible for the magnetic field topology observed in barred galaxies (modes, etc.). We compare our modelled results directly with observations, constructing models of high-frequency (Faraday rotation-free) polarized radio emission maps out of the simulated magnetic field and cosmic ray pattern in our modeled galaxy. We also take the effects of projection into account as well as the limited resolution. Methods. We applied global 3D numerical calculations of a cosmic-ray driven dynamo in barred galaxies with different physical input parameters such as the supernova (SN) rate. Results. Our simulation results lead to the modelled magnetic field structure similar to the one observed on the radio maps of barred galaxies. Moreover, they cast new light on a number of properties in barred and spiral galaxies, such as fast exponential growth of the total magnetic energy to the present values. The quadrupole modes of magnetic field are often identified in barred galaxies, but the dipole modes (e.g., in NGC 4631) are found very seldom. In our simulations the quadrupole configuration dominates and the dipole configuration only appears once in the case of model S100, apparently as a consequence of the choice of the random number seed. Synthetic radio maps of our models display X-type structure similar to what is observed in real galaxies. Conclusions. We conclude that a cosmic-ray driven dynamo process in barred galaxies can amplify magnetic fields efficiently. The fastest rate of magnetic field increase is 195 yr for a SN frequency of 1/50 yr −1 .The obtained strength of magnetic field corresponds to the observational values (a few μG in spiral arms). The polarization and rotation measure maps also agree with observations. We found the effect of shifting magnetic arms in 4 models (out of the sample of 5).

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Galactic winds and the symmetry properties of galactic magnetic fields

Cited by 57 publications

References 13 publications

H Ii Region Driven Galactic Bubbles and Their Relationship to the Galactic Magnetic Field

H Ii Region Driven Galactic Bubbles and Their Relationship to the Galactic Magnetic Field

The large scale magnetic field structure of the spiral galaxy NGC 5775

The effect of supernova rate on the magnetic field evolution in barred galaxies

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