scholarly journals The Influence of Spiral Arms and Bar on the Large-Scale Galactic Magnetic Field Evolution

1996 ◽  
Vol 171 ◽  
pp. 429-429
Author(s):  
K. Otmianowska-Mazur ◽  
S. von Linden ◽  
H. Lesch
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Pitch Angle ◽  
Large Scale ◽  
Angle Distribution ◽  
Galactic Magnetic Field ◽  
Pitch Angle Distribution ◽  
Spiral Arms ◽  
Nearby Galaxies ◽  
The Magnetic Field

Recent observations of radio polarization from nearby galaxies show that the large-scale galactic magnetic field is aligned with spiral arms and bars and the magnetic field vectors in the interarm regions possess a spiral structure which has the same pitch angle as that in spiral arms. Our present project is going to address the following questions: What is the structure and evolution of the large-scale galactic magnetic field under the influence of spiral and bar structure in a galactic disk? To which extent could the resulting magnetic field account for the observed spiral pattern of magnetic field in nearby galaxies? The model is based on the particle-particle numerical scheme (SPH) involving two components: stars and molecular gas. The magnetic field is connected with the latter one. The magnetic field computations were performed first in two dimensions for 100 velocity fields: from 107 to 109 yrs. The resultant magnetic field is strongly affected by spiral arms, however at the given evolutionary stage its structure is different from the velocity field at the same time. The magnetic pitch angle distribution shows that the magnetic field “remembers” all the past velocity steps. The magnetic pitch angle distribution resulting after beam smoothing could quite well fit observations. The present model with fully 3D velocity field of interstellar gas should clear the problem if the magnetic field under the realistic velocity evolution of gas could explain the observed structure of large-scale magnetic field with constant pitch angle in the whole disk.

scholarly journals 8.14. Magnetic fields in star-forming regions of our Galaxy

1998 ◽  
Vol 184 ◽  
pp. 371-372
Author(s):  
B. Hutawarakorn ◽  
R. J. Cohen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Zeeman Splitting ◽  
Theoretical Work ◽  
Field Configuration ◽  
Galactic Magnetic Field ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Magnetic Field

Masers provide a direct way of measuring magnetic fields in star-forming regions. OH ground-state masers at 18 cm wavelength exhibit strong circular polarization due to Zeeman splitting. The implied magnetic field strength is typically a few mG, which is sufficient for the field to be dynamically important, e.g. in channelling the observed bipolar outflows. Moreover there are indications that magnetic fields in maser regions are aligned with the large-scale Galactic magnetic field (Reid & Silverstein 1990), and that bipolar molecular outflows are also aligned with the local Galactic magnetic field (Cohen, Rowland & Blair 1984). Some theoretical work in fact suggests that the magnetic field is intimately connected with the origin of the molecular outflow (e.g. Pudritz & Norman 1983; Uchida & Shibata 1985). It is therefore important to investigate the magnetic field configuration in these regions in as much detail as possible.

scholarly journals The effect of velocity shear on dynamo action due to rotating convection

2013 ◽  
Vol 717 ◽  
pp. 395-416 ◽  
Author(s):  
D. W. Hughes ◽  
M. R. E. Proctor
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Large Scale ◽  
Mean Field ◽  
Magnetic Reynolds Number ◽  
Velocity Shear ◽  
Magnetic Field Generation ◽  
Dynamo Action ◽  
Rotating Convection ◽  
The Magnetic Field

AbstractRecent numerical simulations of dynamo action resulting from rotating convection have revealed some serious problems in applying the standard picture of mean field electrodynamics at high values of the magnetic Reynolds number, and have thereby underlined the difficulties in large-scale magnetic field generation in this regime. Here we consider kinematic dynamo processes in a rotating convective layer of Boussinesq fluid with the additional influence of a large-scale horizontal velocity shear. Incorporating the shear flow enhances the dynamo growth rate and also leads to the generation of significant magnetic fields on large scales. By the technique of spectral filtering, we analyse the modes in the velocity that are principally responsible for dynamo action, and show that the magnetic field resulting from the full flow relies crucially on a range of scales in the velocity field. Filtering the flow to provide a true separation of scales between the shear and the convective flow also leads to dynamo action; however, the magnetic field in this case has a very different structure from that generated by the full velocity field. We also show that the nature of the dynamo action is broadly similar irrespective of whether the flow in the absence of shear can support dynamo action.

scholarly journals Photoelectron pitch angle distribution near Mars and implications on cross terminator magnetic field connectivity

2020 ◽  
Vol 4 (1) ◽  
pp. 1-6
Author(s):  
YuTian Cao ◽  
◽  
Jun Cui ◽  
XiaoShu Wu ◽  
JiaHao Zhong ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Pitch Angle ◽  
Angle Distribution ◽  
Pitch Angle Distribution

scholarly journals Zeeman splitting of OH masers and the galactic magnetic field

2002 ◽  
Vol 206 ◽  
pp. 371-374 ◽  
Author(s):  
Vincent L. Fish ◽  
Mark J. Reid ◽  
Alice L. Argon ◽  
Karl M. Menten
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Large Scale ◽  
Massive Star ◽  
Milky Way ◽  
Zeeman Splitting ◽  
Galactic Magnetic Field ◽  
Massive Star Formation ◽  
The Magnetic Field

Zeeman measurements of OH masers are used to probe the magnetic field around regions of massive star formation. Previous observations suggested that OH maser field directions were aligned in a clockwise sense in the Milky Way, but recent data from a large-scale VLA survey do not support this hypothesis. However, these observations suggest that the magnetic field of the Milky Way is correlated on kiloparsec scales.

scholarly journals Reconnection and energetic particles at the edge of the exterior cusp

2006 ◽  
Vol 24 (7) ◽  
pp. 1949-1956 ◽  
Author(s):  
T. Asikainen ◽  
K. Mursula
Keyword(s):  
Magnetic Field ◽  
Pitch Angle ◽  
Energetic Particles ◽  
Maximum Energy ◽  
Closed Field ◽  
Angle Distribution ◽  
Pitch Angle Distribution ◽  
Flux Transfer Events ◽  
Cusp Region ◽  
Field Lines

Abstract. In this paper we study flux transfer events (FTE) observed at the post-noon edge of the exterior cusp region by Cluster satellites. During the outbound dayside orbit on 2 February 2003, intense bursts of energetic particles were observed in close conjuction with magnetic field FTE signatures by the RAPID instrument onboard the Cluster 4. The pitch-angle distribution of the particles showed that the enhancements consist of particles flowing antiparallel to the magnetosheath field lines away from the expected reconnection site to the exterior cusp. At the same time Cluster 3 observed enhancements of energetic particles deeper in the exterior cusp with a delay of about 40 s to the Cluster 4 enhancements. The estimated maximum energy gain per particle by reconnection remains below 1 keV, thus clearly below the tens to hundreds of keV energy range observed by the RAPID instrument. These observations support the earlier statistical result of the magnetospheric origin of energetic particles in the exterior cusp. Reconnection near the exterior cusp partly releases the particles in the closed field lines of the adjacent HLPS region into the exterior cusp.

scholarly journals Global enhancement and structure formation of the magnetic field in spiral galaxies

2018 ◽  
Vol 609 ◽  
pp. A104 ◽  
Author(s):  
Sergey A. Khoperskov ◽  
Sergey S. Khrapov
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Large Scale ◽  
Spiral Galaxies ◽  
Mean Field ◽  
Field Structure ◽  
Small Scale ◽  
Spiral Pattern ◽  
Spiral Arms ◽  
The Magnetic Field

In this paper we study numerically large-scale magnetic field evolution and its enhancement in gaseous disks of spiral galaxies. We consider a set of models with the various spiral pattern parameters and the initial magnetic field strength with taking into account gas self-gravity and cooling and heating processes. In agreement with previous studies we find out that galactic magnetic field is mostly aligned with gaseous structures, however small-scale gaseous structures (spurs and clumps) are more chaotic than the magnetic field structure. In spiral arms magnetic field often coexists with the gas distribution, in the inter-arm region we see filamentary magnetic field structure. These filaments connect several isolated gaseous clumps. Simulations reveal the presence of the small-scale irregularities of the magnetic field as well as the reversal of magnetic field at the outer edge of the large-scale spurs. We provide evidences that the magnetic field in the spiral arms has a stronger mean-field component, and there is a clear inverse correlation between gas density and plasma-beta parameter, compared to the rest of the disk with a more turbulent component of the field and an absence of correlation between gas density and plasma-beta. We show the mean field growth up to 3−10 μG in the cold gas during several rotation periods (500−800 Myr), whereas ratio between azimuthal and radial field is equal to 4/1. We find an enhancement of random and ordered components of the magnetic field. Mean field strength increases by a factor of 1.5−2.5 for models with various spiral pattern parameters. Random magnetic field component can reach up to 25% from the total strength. By making an analysis of the time-dependent evolution of the radial Poynting flux, we point out that the magnetic field strength is enhanced more strongly at the galactic outskirts which is due to the radial transfer of magnetic energy by the spiral arms pushing the magnetic field outward. Our results also support the presence of sufficient conditions for the development of magnetorotational instability at distances >11 kpc after 300 Myr of evolution.

scholarly journals NIR polarimetry as a probe of the large-scale structure of the galactic magnetic field

2012 ◽  
Vol 8 (S294) ◽  
pp. 253-254
Author(s):  
Michael D. Pavel
Keyword(s):  
Magnetic Field ◽  
Pitch Angle ◽  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Galactic Magnetic Field ◽  
Galactic Longitude

AbstractH-band (1.6 μm) starlight polarimetry was used to test predictions of the large-scale symmetry of the Galactic magnetic field and to measure the Galactic magnetic pitch angle. Polarimetry was obtained with the Mimir instrument on the 1.8m Perkins Telescope outside of Flagstaff, AZ USA along a line of constant Galactic longitude for a range of Galactic latitudes. Comparison with all-sky predictions of starlight polarimetry allows significant rejection of disk anti-symmetric Galactic magnetic field geometries and favored disk symmetric geometries. The Galactic magnetic field pitch angle was also constrained to be p=–6±2° towards this direction.

scholarly journals Magnetic Field Vector Structure of NGC6946

Galaxies ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 59
Author(s):  
Kohei Kurahara ◽  
Hiroyuki Nakanishi
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Azimuthal Angle ◽  
Outer Region ◽  
Infrared Image ◽  
Field Vector ◽  
Magnetic Vector ◽  
Spiral Arms ◽  
Vector Map ◽  
The Magnetic Field

We studied large-scale magnetic field reversals of a galaxy based on a magnetic vector map of NGC6946. The magnetic vector map was constructed based on the polarization maps in the C and X bands after the determination of the geometrical orientation of a disk with the use of an infrared image and the velocity field, according to the trailing spiral arm assumption. We examined the azimuthal variation of the magnetic vector and found that the magnetic pitch angle changes continually as a function of the azimuthal angle in the inter-arm region. However, the direction of the magnetic field had 180 ∘ jumps at the azimuthal angles of 20 ∘ , 110 ∘ , 140 ∘ , 220 ∘ , 280 ∘ , and 330 ∘ . These reversals seem to be related to the spiral arms since the locations of the jumps are coincident with those of the spiral arms. These six reversals of the magnetic field were seen only in the inner region of NGC6946 whereas four reversals can be identified in the outer region.

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