Enhanced Small-Scale Faraday Rotation in the Galactic Spiral Arms

2006 ◽  
Vol 637 (1) ◽  
pp. L33-L35 ◽  
Author(s):  
M. Haverkorn ◽  
B. M. Gaensler ◽  
J. C. Brown ◽  
N. S. Bizunok ◽  
N. M. McClure-Griffiths ◽  
...  
Keyword(s):  
Faraday Rotation ◽  
Small Scale ◽  
Spiral Arms ◽  
Galactic Spiral

scholarly journals Measuring interstellar magnetic fields by radio synchrotron emission

2008 ◽  
Vol 4 (S259) ◽  
pp. 3-14 ◽  
Author(s):  
Rainer Beck
Keyword(s):  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Milky Way ◽  
Small Scale ◽  
Synchrotron Emission ◽  
Intensity Measures ◽  
Spiral Arms ◽  
Preferred Direction ◽  
Ordered Fields

AbstractRadio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of interstellar magnetic fields. The total intensity traces the strength and distribution of total magnetic fields. Total fields in gas-rich spiral arms and bars of nearby galaxies have strengths of 20–30 μGauss, due to the amplification of turbulent fields, and are dynamically important. In the Milky Way, the total field strength is about 6 μG near the Sun and several 100 μG in filaments near the Galactic Center. – The polarized intensity measures ordered fields with a preferred orientation, which can be regular or anisotropic fields. Ordered fields with spiral structure exist in grand-design, barred, flocculent and even in irregular galaxies. The strongest ordered fields are found in interarm regions, sometimes forming “magnetic spiral arms” between the optical arms. Halo fields are X-shaped, probably due to outflows. – The Faraday rotation of the polarization vectors traces coherent regular fields which have a preferred direction. In some galaxies Faraday rotation reveals large-scale patterns which are signatures of dynamo fields. However, in most galaxies the field has a complicated structure and interacts with local gas flows. In the Milky Way, diffuse polarized radio emission and Faraday rotation of the polarized emission from pulsars and background sources show many small-scale and large-scale magnetic features, but the overall field structure in our Galaxy is still under debate.

scholarly journals Galactic spiral patterns and dynamo action

2012 ◽  
Vol 8 (S294) ◽  
pp. 249-250 ◽  
Author(s):  
Luke Chamandy ◽  
Kandaswamy Subramanian ◽  
Anvar Shukurov
Keyword(s):  
Mean Field ◽  
Small Scale ◽  
Galactic Rotation ◽  
Dynamo Action ◽  
Spiral Arms ◽  
Ngc 6946 ◽  
The Mean ◽  
Galactic Spiral ◽  
Scale Turbulence ◽  
Galactic Dynamos

AbstractThe theory of mean-field galactic dynamos is generalized by allowing for a finite response time of the mean electromotive force (emf) to variations in the mean magnetic field and small-scale turbulence. A non-axisymmetric forcing of the dynamo by a spiral pattern (either stationary or transient) is invoked. The resulting magnetic spiral arms are phase-shifted from the spiral arms of the pattern by an angle 15°–40°, opposite to the sense of galactic rotation. Our findings may help to explain the phase shift between material and magnetic arms observed in NGC 6946 and other galaxies.

scholarly journals Velocity Structures in the Vertical Extensions of Spiral Arms

1983 ◽  
Vol 100 ◽  
pp. 143-144
Author(s):  
J. V. Feitzinger ◽  
J. Spicker
Keyword(s):  
Rolling Motion ◽  
Spiral Arms ◽  
Motion Effect ◽  
Geometrical Effects ◽  
Galactic Spiral

Yuan and Wallace (1973) explained the “Rolling motion” in galactic spiral arms by geometrical means as apparent, but not actual motions. Strauss and Poeppel (1976), however, could demonstrate, that these geometrical effects are not sufficiently large to produce the rolling motions. The aim of this investigation is to explain the remaining part of the rolling motion effect with the galactic fountain model (Bregman 1980).

Star formation in galactic spiral arms

Nature ◽  
1982 ◽  
Vol 297 (5863) ◽  
pp. 179-180
Author(s):  
Gerard Gilmore
Keyword(s):  
Star Formation ◽  
Spiral Arms ◽  
Galactic Spiral

scholarly journals Star formation scales and efficiency in Galactic spiral arms

2015 ◽  
Vol 452 (1) ◽  
pp. 289-300 ◽  
Author(s):  
D. J. Eden ◽  
T. J. T. Moore ◽  
J. S. Urquhart ◽  
D. Elia ◽  
R. Plume ◽  
...  
Keyword(s):  
Star Formation ◽  
Spiral Arms ◽  
Galactic Spiral

Distribution of type Ib/c supernovae relative to galactic spiral arms

2007 ◽  
Vol 33 (11) ◽  
pp. 715-719 ◽  
Author(s):  
G. A. Mikhailova ◽  
O. S. Bartunov ◽  
D. Yu. Tsvetkov
Keyword(s):  
Spiral Arms ◽  
Galactic Spiral

scholarly journals Can we detect Galactic spiral arms? 3D dust distribution in the Milky Way

2017 ◽  
Vol 12 (S330) ◽  
pp. 189-192 ◽  
Author(s):  
Sara Rezaei Kh. ◽  
Coryn A. L. Bailer-Jones ◽  
Morgan Fouesneau ◽  
Richard Hanson
Keyword(s):  
Spatial Correlation ◽  
High Precision ◽  
Milky Way ◽  
Precision Measurements ◽  
Line Of Sight ◽  
Spiral Arms ◽  
Dust Extinction ◽  
The Galaxy ◽  
Galactic Spiral ◽  
Dust Distribution

AbstractWe present a model to map the 3D distribution of dust in the Milky Way. Although dust is just a tiny fraction of what comprises the Galaxy, it plays an important role in various processes. In recent years various maps of dust extinction have been produced, but we still lack a good knowledge of the dust distribution. Our presented approach leverages line-of-sight extinctions towards stars in the Galaxy at measured distances. Since extinction is proportional to the integral of the dust density towards a given star, it is possible to reconstruct the 3D distribution of dust by combining many lines-of-sight in a model accounting for the spatial correlation of the dust. Such a technique can be used to infer the most probable 3D distribution of dust in the Galaxy even in regions which have not been observed. This contribution provides one of the first maps which does not show the “fingers of God” effect. Furthermore, we show that expected high precision measurements of distances and extinctions offer the possibility of mapping the spiral arms in the Galaxy.

scholarly journals Morphological signatures induced by dust back reaction in discs with an embedded planet

2019 ◽  
Vol 491 (4) ◽  
pp. 4702-4718 ◽  
Author(s):  
Chao-Chin Yang (楊朝欽) ◽  
Zhaohuan Zhu (朱照寰)
Keyword(s):  
Large Scale ◽  
Stopping Time ◽  
Dust Particles ◽  
Small Scale ◽  
Thermal Mass ◽  
Back Reaction ◽  
Spiral Arms ◽  
Tightly Coupled ◽  
Dust Component ◽  
Modelling Effort

ABSTRACT Recent observations have revealed a gallery of substructures in the dust component of nearby protoplanetary discs, including rings, gaps, spiral arms, and lopsided concentrations. One interpretation of these substructures is the existence of embedded planets. Not until recently, however, most of the modelling effort to interpret these observations ignored the dust back reaction to the gas. In this work, we conduct local-shearing-sheet simulations for an isothermal, inviscid, non-self-gravitating, razor-thin dusty disc with a planet on a fixed circular orbit. We systematically examine the parameter space spanned by planet mass (0.1Mth ≤ Mp ≤ 1Mth, where Mth is the thermal mass), dimensionless stopping time (10−3 ≤ τs ≤ 1), and solid abundance (0 < Z ≤ 1). We find that when the dust particles are tightly coupled to the gas (τs < 0.1), the spiral arms are less open and the gap driven by the planet becomes deeper with increasing Z, consistent with a reduced speed of sound in the approximation of a single dust–gas mixture. By contrast, when the dust particles are marginally coupled (0.1 ≲ τs ≲ 1), the spiral structure is insensitive to Z and the gap structure in the gas can become significantly skewed and unidentifiable. When the latter occurs, the pressure maximum radially outside of the planet is weakened or even extinguished, and hence dust filtration by a low-mass (Mp < Mth) planet could be reduced or eliminated. Finally, we find that the gap edges where the dust particles are accumulated as well as the lopsided large-scale vortices driven by a massive planet, if any, are unstable, and they are broken into numerous small-scale dust–gas vortices.

scholarly journals Substructure within galactic spiral arms as derived from studies at 21 cm

1959 ◽  
Vol 9 ◽  
pp. 355-359
Author(s):  
R. D. Davies
Keyword(s):  
Fine Structure ◽  
High Resolution ◽  
Velocity Dispersion ◽  
Detailed Structure ◽  
Hydrogen Line ◽  
Spiral Arms ◽  
Frequency Structure ◽  
Galactic Spiral ◽  
Spiral Arm

Detailed structure within the spiral arms of our Galaxy is suggested by hydrogen-line spectra taken with high resolution in frequency [1]. The spectra show much detail in each maximum (spiral arm). It is not clear, however, if this frequency structure refers to fine structure in depth or in velocity dispersion or in both. Fine structure in position and depth has been inferred from 21-cm drift curves taken across the nearby spiral arms. The results of three investigations will be discussed. Two have been published in some detail [2, 3] and will only be summarized here.

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