scholarly journals The role of the random magnetic fields in the ISM: HVC numerical simulations

2008 ◽  
Vol 4 (S259) ◽  
pp. 91-92
Author(s):  
Alfredo Santillán ◽  
J. Kim ◽  
F. J. Sánchez-Salcedo ◽  
J. Franco ◽  
L. Hernández-Cervantes
Keyword(s):  
Magnetic Field ◽  
Numerical Simulations ◽  
High Latitude ◽  
High Velocity ◽  
Random Component ◽  
Galactic Magnetic Field ◽  
Random Magnetic Field ◽  
The Mean ◽  
High Velocity Clouds

AbstractWe know that the galactic magnetic field possesses a random component in addition to the mean uniform component, with comparable strength of the two components. This random component is considered to play important roles in the evolution of the interstellar medium (ISM). In this work we present numerical simulations associated with the interaction of the supersonic flows located at high latitude in our Galaxy (High Velocity Clouds, HVC) with the magnetized galactic ISM in order to study the effect that produces a random magnetic field in the evolution of this objects.

scholarly journals Statistical simulations of the dust foreground to cosmic microwave background polarization

2017 ◽  
Vol 603 ◽  
pp. A62 ◽  
Author(s):  
F. Vansyngel ◽  
F. Boulanger ◽  
T. Ghosh ◽  
B. Wandelt ◽  
J. Aumont ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Cosmic Microwave Background ◽  
Power Spectra ◽  
Random Component ◽  
Galactic Magnetic Field ◽  
Microwave Background ◽  
Total Dust ◽  
The Mean ◽  
Polarization Spectra ◽  
The Magnetic Field

The characterization of the dust polarization foreground to the cosmic microwave background (CMB) is a necessary step toward the detection of the B-mode signal associated with primordial gravitational waves. We present a method to simulate maps of polarized dust emission on the sphere that is similar to the approach used for CMB anisotropies. This method builds on the understanding of Galactic polarization stemming from the analysis of Planck data. It relates the dust polarization sky to the structure of the Galactic magnetic field and its coupling with interstellar matter and turbulence. The Galactic magnetic field is modeled as a superposition of a mean uniform field and a Gaussian random (turbulent) component with a power-law power spectrum of exponent αM. The integration along the line of sight carried out to compute Stokes maps is approximated by a sum over a small number of emitting layers with different realizations of the random component of the magnetic field. The model parameters are constrained to fit the power spectra of dust polarization EE, BB, and TE measured using Planck data. We find that the slopes of the E and B power spectra of dust polarization are matched for αM = −2.5, an exponent close to that measured for total dust intensity but larger than the Kolmogorov exponent − 11/3. The model allows us to compute multiple realizations of the Stokes Q and U maps for different realizations of the random component of the magnetic field, and to quantify the variance of dust polarization spectra for any given sky area outside of the Galactic plane. The simulations reproduce the scaling relation between the dust polarization power and the mean total dust intensity including the observed dispersion around the mean relation. We also propose a method to carry out multifrequency simulations, including the decorrelation measured recently by Planck, using a given covariance matrix of the polarization maps. These simulations are well suited to optimize component separation methods and to quantify the confidence with which the dust and CMB B-modes can be separated in present and future experiments. We also provide an astrophysical perspective on our phenomenological modeling of the dust polarization spectra.

scholarly journals A dynamo amplifying the magnetic field of a Milky-Way-like galaxy

2020 ◽  
Vol 641 ◽  
pp. A165
Author(s):  
Evangelia Ntormousi ◽  
Konstantinos Tassis ◽  
Fabio Del Sordo ◽  
Francesca Fragkoudi ◽  
Rüdiger Pakmor
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Spiral Galaxies ◽  
Mean Field ◽  
Dark Matter Halo ◽  
Random Component ◽  
Galactic Magnetic Field ◽  
The Mean ◽  
The Magnetic Field ◽  
Mean Field Dynamo

Context. The magnetic fields of spiral galaxies are so strong that they cannot qualify as primordial. Their typical values are over one billion times higher than any value predicted for the early Universe. Explaining this immense growth and incorporating it in galaxy evolution theories is one of the long-standing challenges in astrophysics. Aims. So far, the most successful theory for the sustained growth of the galactic magnetic field is the alpha-omega dynamo. This theory predicts a characteristic dipolar or quadrupolar morphology for the galactic magnetic field, which has been observed in external galaxies. So far, however, there has been no direct demonstration of a mean-field dynamo operating in direct, multi-physics simulations of spiral galaxies. We carry out such a demonstration in this work. Methods. We employed numerical models of isolated, star-forming spiral galaxies that include a magnetized gaseous disk, a dark matter halo, stars, and stellar feedback. Naturally, the resulting magnetic field has a complex morphology that includes a strong random component. Using a smoothing of the magnetic field on small scales, we were able to separate the mean from the turbulent component and analyze them individually. Results. We find that a mean-field dynamo naturally occurs as a result of the dynamical evolution of the galaxy and amplifies the magnetic field by an order of magnitude over half a Gyr. Despite the highly dynamical nature of these models, the morphology of the mean component of the field is identical to analytical predictions. Conclusions. This result underlines the importance of the mean-field dynamo in galactic evolution. Moreover, by demonstrating the natural growth of the magnetic field in a complex galactic environment, it brings us a step closer to understanding the cosmic origin of magnetic fields.

scholarly journals The Structure of the Galactic Magnetic Field toward the High‐Latitude Clouds

1997 ◽  
Vol 476 (2) ◽  
pp. 717-729 ◽  
Author(s):  
Ana I. Gomez de Castro ◽  
Ralph E. Pudritz ◽  
Pierre Bastien
Keyword(s):  
Magnetic Field ◽  
High Latitude ◽  
Galactic Magnetic Field

scholarly journals Wave Structure within HI Filaments at High Galactic Latitude and the Nature of “Clouds” in Interstellar Space

1991 ◽  
Vol 144 ◽  
pp. 93-96
Author(s):  
Gerrit L. Verschuur
Keyword(s):  
High Resolution ◽  
High Latitude ◽  
High Velocity ◽  
Large Amplitude ◽  
Wave Structure ◽  
Interstellar Space ◽  
Galactic Latitude ◽  
High Galactic Latitude ◽  
Field Geometry ◽  
High Velocity Clouds

Large amplitude waves have been found in the morphology and velocity patterns of several long filaments of HI at high latitude. HI in the filaments is controlled by magnetic fields and the velocity patterns and morphology bear the hallmarks of Alfvén waves. Enhanced emission features (EEFs), traditionally referred to as “clouds,” are seen wherever a segment of flux tube is viewed end-on. This suggests that HI emission structure teaches us about field geometry and not about cloud physics. Similar effects have been recognized in other regions mapped with high-resolution as well as in completely mapped high-velocity “clouds.”

scholarly journals Nonlinear Dynamo in a Disk Galaxy

1993 ◽  
Vol 157 ◽  
pp. 349-353
Author(s):  
A. Poezd ◽  
A. Shukurov ◽  
D.D. Sokoloff
Keyword(s):  
Magnetic Field ◽  
Milky Way ◽  
Dynamo Model ◽  
The Galaxy ◽  
Seed Field ◽  
Andromeda Nebula ◽  
The Mean ◽  
Dynamo Equation ◽  
The Magnetic Field

A nonlinear thin-disk galactic dynamo model based on α-quenching is proposed. Assuming that the mean helicity depends on the magnetic field strength averaged across the disk, we derive a universal form of nonlinearity in the radial dynamo equation. We discuss the evolution of the regular magnetic field in the Milky Way and the Andromeda Nebula. It is argued that the reversals of the regular magnetic field in the Galaxy are a relic inherited from the structure of the seed field. We also briefly discuss the role of the turbulent diamagnetism and the effects of galactic evolution on the dynamo.

scholarly journals Microstructure of the Galactic Magnetic Field

1958 ◽  
Vol 8 ◽  
pp. 952-954
Author(s):  
K. Serkowski
Keyword(s):  
Magnetic Field ◽  
Position Angle ◽  
Mean Value ◽  
Open Clusters ◽  
Electric Vector ◽  
Stokes Parameters ◽  
Galactic Magnetic Field ◽  
The Mean ◽  
Image Position

The polarization of the stars in open clusters, explained on the basis of the Davis-Greenstein theory, gives some information on the microstructure of the galactic magnetic field.The polarization is most conveniently described by the parameters Q, U, proportional to the Stokes parameters and defined by where p is the amount of polarization, θ is the position angle of the electric vector, and θ̄ is the mean value of θ for the region under consideration.

scholarly journals The Role of Magnetic Fields in Star Forming Regions

1990 ◽  
Vol 140 ◽  
pp. 259-267
Author(s):  
L Mestel
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
The Self ◽  
Galactic Magnetic Field ◽  
Star Forming ◽  
Star Forming Regions

The flux from the galactic magnetic field alters radically the appropriate description of the equilibrium, collapse and fragmentation of the self-gravitating gas clouds that are the locale of star formation.

scholarly journals REMOTE NUMERICAL SIMULATIONS OF THE INTERACTION OF HIGH VELOCITY CLOUDS WITH RANDOM MAGNETIC FIELDS

2007 ◽  
Vol 40 (4) ◽  
pp. 165-169 ◽  
Author(s):  
Alfredo Santikkan ◽  
Liliana Hernandez-Cervantes ◽  
Alejandro Gonzalez-Ponce ◽  
Jong-Soo Kim
Keyword(s):  
Magnetic Fields ◽  
Numerical Simulations ◽  
High Velocity ◽  
High Velocity Clouds
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