The relative orientation between the magnetic field and gas density structures in non-gravitating turbulent media

ABSTRACT Magnetic fields are a dynamically important agent for regulating structure formation in the interstellar medium. The study of the relative orientation between the local magnetic field and gas (column-) density gradient has become a powerful tool to analyse the magnetic field’s impact on the dense gas formation in the Galaxy. In this study, we perform numerical simulations of a non-gravitating, isothermal gas, where the turbulence is driven either solenoidally or compressively. We find that only simulations with an initially strong magnetic field (plasma-β < 1) show a change in the preferential orientation between the magnetic field and isodensity contours, from mostly parallel at low densities to mostly perpendicular at higher densities. Hence, compressive turbulence alone is not capable of inducing the transition observed towards nearby molecular clouds. At the same high initial magnetization, we find that solenoidal modes produce a sharper transition in the relative orientation with increasing density than compressive modes. We further study the time evolution of the relative orientation and find that it remains unchanged by the turbulent forcing after one dynamical time-scale.

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Using Herschel and Planck observations to delineate the role of magnetic fields in molecular cloud structure

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935779 ◽

2019 ◽

Vol 629 ◽

pp. A96 ◽

Cited By ~ 19

Author(s):

Juan D. Soler

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Molecular Clouds ◽

Thermal Emission ◽

Relative Orientation ◽

Young Stellar Objects ◽

Circular Statistics ◽

Stellar Objects ◽

Submillimeter Wavelengths ◽

The Magnetic Field

We present a study of the relative orientation between the magnetic field projected onto the plane of sky (B⊥) on scales down to 0.4 pc, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the distribution of gas column density (NH) structures on scales down to 0.026 pc, derived from the observations by Herschel in submillimeter wavelengths, toward ten nearby (d < 450 pc) molecular clouds. Using the histogram of relative orientation technique in combination with tools from circular statistics, we found that the mean relative orientation between NH and B⊥ toward these regions increases progressively from 0°, where the NH structures lie mostly parallel to B⊥, with increasing NH, in many cases reaching 90°, where the NH structures lie mostly perpendicular to B⊥. We also compared the relative orientation between NH and B⊥ and the distribution of NH, which is characterized by the slope of the tail of the NH probability density functions (PDFs). We found that the slopes of the NH PDF tail are steepest in regions where NH and B⊥ are close to perpendicular. This coupling between the NH distribution and the magnetic field suggests that the magnetic fields play a significant role in structuring the interstellar medium in and around molecular clouds. However, we found no evident correlation between the star formation rates, estimated from the counts of young stellar objects, and the relative orientation between NH and B⊥ in these regions.

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What are we learning from the relative orientation between density structures and the magnetic field in molecular clouds?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731049 ◽

2017 ◽

Vol 607 ◽

pp. A2 ◽

Cited By ~ 34

Author(s):

J. D. Soler ◽

P. Hennebelle

Keyword(s):

Magnetic Field ◽

Molecular Clouds ◽

Relative Orientation ◽

The Magnetic Field

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The Magnetic Field of the Galaxy

Physical Review ◽

10.1103/physrev.70.777 ◽

1946 ◽

Vol 70 (9-10) ◽

pp. 777-778 ◽

Cited By ~ 6

Author(s):

Lyman Spitzer

Keyword(s):

Magnetic Field ◽

The Galaxy ◽

The Magnetic Field

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The Origin and Dynamical Effects of the Magnetic Fields and Cosmic Rays in the Disk of the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900004873 ◽

1970 ◽

Vol 39 ◽

pp. 168-183

Author(s):

E. N. Parker

Keyword(s):

Magnetic Field ◽

Cosmic Rays ◽

Magnetic Fields ◽

Dynamical Behavior ◽

Cosmic Ray ◽

Interested Reader ◽

Written Text ◽

The Galaxy ◽

Basic Ideas ◽

The Magnetic Field

The topic of this presentation is the origin and dynamical behavior of the magnetic field and cosmic-ray gas in the disk of the Galaxy. In the space available I can do no more than mention the ideas that have been developed, with but little explanation and discussion. To make up for this inadequacy I have tried to give a complete list of references in the written text, so that the interested reader can pursue the points in depth (in particular see the review articles Parker, 1968a, 1969a, 1970). My purpose here is twofold, to outline for you the calculations and ideas that have developed thus far, and to indicate the uncertainties that remain. The basic ideas are sound, I think, but, when we come to the details, there are so many theoretical alternatives that need yet to be explored and so much that is not yet made clear by observations.

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Numerical Analysis of Air Convection in a Vertical Cylindrical Container With and Without a Gravitational Field Under a Gradient of a Magnetic Field

Computational Technologies for Fluid/Thermal/Structural/Chemical Systems With Industrial Applications, Volume 1 ◽

10.1115/pvp2002-1539 ◽

2002 ◽

Author(s):

Masato Akamatsu ◽

Mitsuo Higano ◽

Yoshio Takahashi ◽

Hiroyuki Ozoe

Keyword(s):

Magnetic Field ◽

Gravitational Field ◽

Transfer Rate ◽

Relative Orientation ◽

Axial Position ◽

Cylindrical Container ◽

Gravitational Fields ◽

Air Convection ◽

Magnetizing Force ◽

The Magnetic Field

Two-dimensional numerical computations were carried out for natural convection of air in a vertical cylindrical container with and without a gravitational field under a gradient of a magnetic field. The magnetic field and the magnetizing force were induced in the cylinder area and the strength and the vectors of the magnetizing force were dependent on the axial location of the electric coil. Sample computations were carried out by changing the relative orientation of an electric coil and container. In a gravitational field, air in a cylindrical container was driven by both gravitational and magnetizing forces. On the other hand, the air flow was induced by the magnetizing force even in a non-gravitational field. Flow pattern and the heat transfer rate greatly depended on the axial position of the electric coil under both gravitational and non-gravitational fields.

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Observability of the Magnetic Field in Molecular Clouds

Symposium - International Astronomical Union ◽

10.1017/s007418090019028x ◽

1990 ◽

Vol 140 ◽

pp. 304-304

Author(s):

N. Bel ◽

B. Leroy

Keyword(s):

Magnetic Field ◽

Molecular Clouds ◽

Diatomic Molecules ◽

Zeeman Effect ◽

Interstellar Clouds ◽

The Magnetic Field

We have done detailed calculations of the Zeeman effect in the dozen diatomic molecules identified in interstellar clouds.

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Solitary potential structures observed in the magnetosheath by the Cluster spacecraft

Nonlinear Processes in Geophysics ◽

10.5194/npg-10-3-2003 ◽

2003 ◽

Vol 10 (1/2) ◽

pp. 3-11 ◽

Cited By ~ 67

Author(s):

J. S. Pickett ◽

J. D. Menietti ◽

D. A. Gurnett ◽

B. Tsurutani ◽

P. M. Kintner ◽

...

Keyword(s):

Magnetic Field ◽

Time Series Data ◽

Broad Band ◽

Low Frequency ◽

Bow Shock ◽

Local Magnetic Field ◽

Series Data ◽

The Individual ◽

Almost All ◽

The Magnetic Field

Abstract. Bipolar pulses of ~ 25-100 µs in duration have been observed in the wave electric field data obtained by the Wideband plasma wave instrument on the Cluster spacecraft in the dayside magnetosheath. These pulses are similar in almost all respects to those observed on several spacecraft over the last few years. They represent solitary potential structures, and in this case, electron phase space holes. When the time series data containing the bipolar pulses on Cluster are transformed to the frequency domain by a windowed FFT, the pulses appear as typical broad-band features, extending from the low-frequency cutoff of the bandpass filter, ~ 1 kHz, up to as great as 20-40 kHz in some cases, with decreasing intensity as the frequency increases. The upper frequency cutoff of the broad band is an indication of the individual pulse durations (1/f). The solitary potential structures are detected when the local magnetic field is contained primarily in the spin plane, indicating that they propagate along the magnetic field. Their frequency extent and intensity seem to increase as the angle between the directions of the magnetic field and the plasma flow decreases from 90°. Of major significance is the finding that the overall profile of the broad-band features observed simultaneously by two Cluster spacecraft, separated by a distance of over 750 km, are strikingly similar in terms of onset times, frequency extent, intensity, and termination. This implies that the generation region of the solitary potential structures observed in the magnetosheath near the bow shock is very large and may be located at or near the bow shock, or be connected with the bow shock in some way.

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Study of the Magnetic Field of the Galaxy using Correlation Functions of the Intensity of Synchrotron Background Radio Emission

Symposium - International Astronomical Union ◽

10.1017/s0074180900230441 ◽

1996 ◽

Vol 169 ◽

pp. 615-616

Author(s):

V.R. Shoutenkov

Keyword(s):

Magnetic Field ◽

Radio Emission ◽

Correlation Functions ◽

Theoretical Calculations ◽

Angular Separation ◽

Field Studies ◽

Position Angle ◽

The Galaxy ◽

Image Position ◽

The Magnetic Field

The possibility to study magnetic field of the Galaxy calculating correlation or structure functions of synchrotron background radio emission have been known long ago (Kaplan and Pikel'ner (1963); Getmantsev (1958)). But this method had not been as popular as other methods of magnetic field studies. However theoretical calculations made by Chibisov and Ptuskin (1981) showed that correlation functions of intensity of synchrotron background radio emission can give a lot of valuable information about galactic magnetic fields because of the intensity of synchrotron background radio emission depends on H⊥. According to this theory correlation C(θ, φ) and structure S(θ, φ) functions of intensity, as functions of angular separation θ between two lines of sight and position angle φ on the sky between this two lines of sight, can be presented as a sum of isotropic (not dependent from angle φ) and anisotropic parts:

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Accretion Disc Formation in Intermediate Polars

International Astronomical Union Colloquium ◽

10.1017/s0252921100038501 ◽

1996 ◽

Vol 158 ◽

pp. 161-164

Author(s):

G. A. Wynn ◽

A. R. King

Keyword(s):

Magnetic Field ◽

Accretion Disc ◽

Local Magnetic Field ◽

Magnetic Systems ◽

X Ray ◽

Accretion Flow ◽

Intermediate Polars ◽

X Ray Binaries ◽

The Magnetic Field ◽

Disc Formation

The large-scale accretion flow in the intermediate polars (IPs) is still a matter of vigorous debate. It is known that the magnetic field of the white dwarf (WD) controls the accretion flow close to the surface, channeling the plasma onto the polecaps and giving rise to X-ray emission modulated at the WD spin period (Pspin). After their discovery it was assumed that IPs were the WD analogues of the pulsing X-ray binaries, where a magnetic neutron star accretes from a disrupted accretion disc. However, a number of authors have pointed out that the criteria for disc formation in IPs are less certain than those for the X-ray binaries.The simplest possible criterion for disc formation in a binary is that the accretion flow should be able to orbit freely about the primary star (see Frank, King & Raine 1991 for a review). In non-magnetic systems this is merely the condition that the minimum approach distance of the free stream (Rmin) should exceed the radius of the primary. The situation in magnetic systems is more complex, as the magnetic field of the primary presents an obstacle to the infalling accretion stream. In many treatments of IPs it is assumed that the plasma stream is able to orbit freely about the WD until the ram pressure of the stream is of the same order as the magnetic pressureρv2~B2/8π, whereρis the stream density,vthe stream velocity andBthe local magnetic field strength. This condition fixes the magnetospheric radius,Rmag, inside which the magnetic field is assumed to thread the stream material and direct the accretion flow along the fieldlines.

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