Electric dipole moments and disalignment of interstellar dust grains

Jordan, Margaret E.; Weingartner, Joseph C.

doi:10.1111/j.1365-2966.2009.15480.x

Cited by 12 publications

(8 citation statements)

References 35 publications

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“…Second, the grain randomization due to the electric field acting on the electric dipole moment of grains that are accelerated by interstellar turbulence (Lazarian & Yan 2002;Yan & Lazarian 2003;Yan et al 2004;Yan 2009;Hoang et al 2012) is found to decrease (i.e., the degree of RAT alignment is increased) when the magnetic field is increased. The effect of such a randomization is described in Weingartner (2006) and (Jordan & Weingartner 2009). 9 For a weak magnetic field, the randomization is thought to be more important because the rate of Larmor precession is lower than the rate of dipole fluctuations.…”

Section: Excess Uv Polarization and Alignment Of Smallmentioning

confidence: 99%

Paramagnetic Alignment of Small Grains: A Novel Method for Measuring Interstellar Magnetic Fields

Hoang

Lazarían

Martín

2014

ApJ

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We present a novel method to measure the strength of interstellar magnetic fields using ultraviolet (UV) polarization of starlight that is in part produced by weakly aligned, small dust grains. We begin with calculating the degrees of the paramagnetic alignment of small (size a ∼ 0.01 μm) and very small (a ∼ 0.001 μm) grains in the interstellar magnetic field due to the Davis-Greenstein relaxation and resonance relaxation. To calculate the degrees of paramagnetic alignment, we use Langevin equations and take into account various interaction processes essential for the rotational dynamics of small grains. We find that the alignment of small grains is necessary to reproduce the observed polarization in the UV, although the polarization arising from these small grains is negligible at the optical and infrared (IR) wavelengths. Based on fitting theoretical models to observed extinction and polarization curves, we find that the best-fit model for the case with the peak wavelength of polarization λ max < 0.55 μm requires a higher degree of alignment of small grains than for the typical case with λ max = 0.55 μm. We interpret the correlation between the systematic increase of the UV polarization relative to maximum polarization (i.e., of p(6 μm −1 )/p max ) with λ −1 max for cases of low λ max by appealing to the higher degree of alignment of small grains. We utilize the correlation of the paramagnetic alignment of small grains with the magnetic field strength B to suggest a new way to measure B using the observable parameters λ max and p(6 μm −1 )/p max .

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Section: Excess Uv Polarization and Alignment Of Smallmentioning

confidence: 99%

Paramagnetic Alignment of Small Grains: A Novel Method for Measuring Interstellar Magnetic Fields

Hoang

Lazarían

Martín

2014

ApJ

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“…Within our study, we use the estimate of grain charge to evaluate the rate of grain Larmor rotation about a magnetic field, and we use the grain dipole moment estimates from Weingartner (2009) and Jordan & Weingartner (2009). In future publications, we intend to address the modification of alignment processes for carbonaceous grains of different sizes and composition by the variations of grain charging, as well as the variations in the grain electric dipole moment (see Appendix A).…”

Section: Environment Of Carbonaceous Grainsmentioning

confidence: 99%

Two modes of carbonaceous dust alignment

Lazarian

2020

Preprint

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Radiative Torques (RATs) or Mechanical Torques (METs) acting on irregular grains can induce the alignment of dust grains in respect to the alignment axis (AA), which can be either the direction of the magnetic field, or the direction of the radiation. We show that carbonaceous grains can be aligned with their axes both parallel and perpendicular to the AA and we explore the conditions where the particular mode of alignment takes place. We identify a new process of alignment of charged carbonaceous grains in a turbulent magnetized interstellar medium with respect to an electric field. This field acts on grains accelerated in a turbulent medium and gyro-rotating about a magnetic field. The electric field can also arise from the temporal variations of magnetic field strength in turbulent compressible media. The direction of the electric field is perpendicular to a magnetic field and the carbonaceous grains precess in the electric field because of their electric moments. If this precession is faster than Larmor precession in the magnetic field, the alignment of such grains is with their long axes parallel to magnetic field. We explore the parameter space for which the new mechanism aligns grains with long axes parallel to the magnetic field. We compare this mechanism with another process that provides the same type of alignment, namely, the RAT alignment of grains with insufficiently fast internal relaxation. We describe the conditions for which the particular mode of carbonaceous grain alignment is realized and discuss what information can be obtained by measuring the resulting polarization.

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“…The diffuse polarized Galactic synchrotron emission is produced by relativistic electrons that spiral along the GMF lines (see Ginzburg & Syrovatskiȋ 1966, for a review). Equivalently, the polarized thermal dust emission is produced by rotating aspherical dust grains that are totally or partially aligned with the GMF lines (Davis & Greenstein 1951;King & Harwit 1973;Onaka 1996;Lazarian et al 1996;Onaka 2000;Efroimsky 2002;Jordan & Weingartner 2009;Vaillancourt et al 2013;Andersson et al 2015;Hoang 2017).…”

Section: Introductionmentioning

confidence: 99%

“…The diffuse polarized Galactic synchrotron emission is produced by relativistic electrons that spiral along the Galactic magnetic field (GMF) lines (see Ginzburg & Syrovatski ȋ 1966, for a review). Equivalently, the polarized thermal dust emission is produced by rotating prolate dust grains totally or partially aligned by the GMF lines (Davis & Greenstein 1951;King & Harwit 1973;Onaka 1996;Lazarian et al 1996;Onaka 2000; Efroimsky 1 http://www.radioforegrounds.eu/ 2002; Jordan & Weingartner 2009;Vaillancourt et al 2013;Andersson et al 2015;Hoang 2017). Therefore, a combined study of the diffuse synchrotron and thermal dust polarized Galactic emission should in principle allow us to constrain the GMF properties and the Galaxy matter content.…”

Section: Introductionmentioning

confidence: 99%

Galactic magnetic field reconstruction using the polarized diffuse Galactic emission: formalism and application to Planck data

Pelgrims

Macías-Pérez

Ruppin

2021

A&A

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The polarized Galactic synchrotron and thermal dust emission constitutes a major tool in the study of the Galactic magnetic field (GMF) and in constraining its strength and geometry for the regular and turbulent components. In this paper, we review the modeling of these two components of the polarized Galactic emission and present our strategy for optimally exploiting the currently existing data sets. We investigate a Markov chain Monte Carlo (MCMC) method to constrain the model parameter space through maximum-likelihood analysis, focusing mainly on dust polarized emission. Relying on simulations, we demonstrate that our methodology can be used to constrain the regular GMF geometry. Fitting for the reduced Stokes parameters, this reconstruction is only marginally dependent of the accuracy of the reconstruction of the Galactic dust grain density distribution. However, the reconstruction degrades, apart from the pitch angle, when including a turbulent component on the order of the regular one as suggested by current observational constraints. Finally, we applied this methodology to a set of Planck polarization maps at 353 GHz to obtain the first MCMC based constrains on the large-scale regular-component of the GMF from the polarized diffuse Galactic thermal dust emission. By testing various models of the dust density distribution and of the GMF geometry, we prove that it is possible to infer the large-scale geometrical properties of the GMF. We obtain coherent three-dimensional views of the GMF, from which we infer a mean pitch angle of 27 degrees with 14% scatter, which is in agreement with results obtained in the literature from synchrotron emission.

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Electric dipole moments and disalignment of interstellar dust grains

Cited by 12 publications

References 35 publications

Paramagnetic Alignment of Small Grains: A Novel Method for Measuring Interstellar Magnetic Fields

Paramagnetic Alignment of Small Grains: A Novel Method for Measuring Interstellar Magnetic Fields

Two modes of carbonaceous dust alignment

Galactic magnetic field reconstruction using the polarized diffuse Galactic emission: formalism and application to Planck data

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