A Technique for Constraining the Driving Scale of Turbulence and a Modified Chandrasekhar–fermi Method

Cho, Jungyeon; Yoo, Hyunju

doi:10.3847/0004-637x/821/1/21

Cited by 66 publications

(97 citation statements)

References 27 publications

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“…Simulations show that this estimate can be corrected for a statistical ensemble of objects to yield realistic estimates of the field strength (Heitsch et al 2001;Ostriker et al 2001;Falceta-Gonçalves et al 2008). In addition, the effects of multiple eddies along the line of sight have been studied by Cho & Yoo (2016).…”

Section: Observing Magnetic Fieldsmentioning

confidence: 99%

First Results from BISTRO: A SCUBA-2 Polarimeter Survey of the Gould Belt

Ward-Thompson

Pattle

Bastien

et al. 2017

ApJ

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104

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We present the first results from the B-fields In STar-forming Region Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer Array2 camera, with its associated polarimeter (POL-2), on the James Clerk Maxwell Telescope in Hawaii. We discuss the survey's aims and objectives. We describe the rationale behind the survey, and the questions thatthe survey will aim to answer. The most important of these is the role of magnetic fields in the star formation process on the scale of individual filaments and cores in dense regions. We describe the data acquisition and reduction processes for POL-2, demonstrating both repeatability and consistency with previous data. We present a first-look analysis of the first results from the BISTRO survey in the OMC1 region. We see that the magnetic field lies approximately perpendicular to the famous "integral filament" in the densest regions of that filament. Furthermore, we see an "hourglass" magnetic field morphology extending beyond the densest region of the integral filament into the less-dense surrounding material, and discuss possible causes for this. We also discuss the more complex morphology seen along the Orion Bar region. We examine the morphology of the field along the lower-density northeastern filament. We find consistency with previous theoretical models that predict magnetic fields lying parallel to low-density, non-self-gravitating filaments, and perpendicular to higher-density, self-gravitating filaments.

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Section: Observing Magnetic Fieldsmentioning

confidence: 99%

First Results from BISTRO: A SCUBA-2 Polarimeter Survey of the Gould Belt

Ward-Thompson

Pattle

Bastien

et al. 2017

ApJ

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104

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“…We have shown that the conventional CF method tends to overestimate B 3D 0,sky if the driving scale is smaller than the system size and proposed a modified CF method that can correct the effect. The method we propose in Equation (23) with 0.7 < ξ ′ < 1.0 does not require new observations [5]. That is, the method is readily applicable for present observational data.…”

Section: Numerical Tests Of the Modified Cf Methodsmentioning

confidence: 93%

“…As we can see in the figure, the conventional CF method overestimates B 3D 0,sky as N eddy (∼ 1/k f ) increases. proportional to √ N eddy (see [5] for details). The centroid velocity is a kind of average velocity.…”

Section: Numerical Tests Of the Conventional Cf Methodsmentioning

confidence: 99%

“…We use direct numerical simulations to test the conventional CF method (see [5] for details). We solve the following compressible MHD equations in a periodic box of size 2π using an Essentially Non-Oscillatory scheme (see [9]):…”

Section: Numerical Tests Of the Conventional Cf Methodsmentioning

confidence: 99%

“…Note that N eddy ≈ L sys /L f in simulation data. In Section 3, we introduce our modified CF method (see [5] for details). In Section 4, we provide discussions and summary.…”

Section: Introductionmentioning

confidence: 99%

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Effects of driving scale on astrophysical turbulence and a modified Chandrasekhar-Fermi method

Cho

2017

J. Phys.: Conf. Ser.

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Abstract. Many astrophysical fluids are in turbulent state. To maintain turbulence, energy must be injected into the fluid. In turbulence simulations, it is customary to drive the fluids on a scale comparable to the size of the computational domain. In this paper, we show how some statistics of turbulence, especially turbulence statistics projected on the plane of the sky, is changed when we do not follow the conventional approach. As an example of such a statistics, we discuss in detail how the Chandrasekhar-Fermi method is affected by the small-scale driving, which is a simple and powerful technique for estimating the strength of the mean magnetic field projected on the plane of the sky. IntroductionDriving is required to initiate and maintain turbulence. When hydrodynamic turbulence is driven on a scale L f , the injected energy cascades down to small scales and, when the energy cascade reaches the dissipation scale L d , the energy is lost through viscous damping. The energy spectrum of turbulence peaks at the driving wavenumber k f and shows a power-law scaling in the range between k f and the dissipation wave number k d . The spectrum drops rapidly for wavenumbers larger than k d .In turbulence simulations, the driving scale L f is usually very close to the computational box size L sys . The reason for this is to maximize the inertial range. Let us assume L sys = 2π throughout the paper. In most turbulence simulations, the dissipation wavenumber k d is determined by the numerical resolution: k d is slightly smaller than the maximum wavenumber N x /2, where N x is the number of grid points in one direction. Therefore, in order to maximize the inertial range, it is necessary to drive turbulence near k ∼ 1, which means k f ∼ 1 andIn astronomy, observed quantities are usually integrated along the line-of-sight (LOS). Since observed quantities are two-dimensional (2D) data, obtaining three-dimensional (3D) quantities from observations is not easy. Nevertheless, there are techniques developed to derive 3D turbulence properties from 2D observations. However, those techniques have an intrinsic shortcoming: it is difficult to verify them. To overcome this difficulty, people use computer simulation data to verify their techniques.One such example is the Chandrasekhar-Fermi (CF) method [1], which is a powerful technique for estimating the strength of the plane-of-the-sky component of the mean magnetic field, B 0,sky . The CF method makes use of polarized emission from magnetically aligned dust grains. In the

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Ultraviolet spectropolarimetry with polstar: interstellar medium science

Andersson

Clayton

Doney

et al. 2022

Astrophys Space Sci

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Continuum polarization over the UV-to-microwave range is due to dichroic extinction (or emission) by asymmetric, aligned dust grains. Scattering can also be an important source of polarization, especially at short wavelengths. Because of both grain alignment and scattering physics, the wavelength dependence of the polarization, generally, traces the size of the aligned grains. Similarly because of the differing wavelength dependencies of dichroic extinction and scattering polarization, the two can generally be reliably separated. Ultraviolet (UV) polarimetry therefore provides a unique probe of the smallest dust grains (diameter$< 0.09~\upmu \text{m}$ < 0.09 μm ), their mineralogy and interaction with the environment. However, the current observational status of interstellar UV polarization is very poor with less than 30 lines of sight probed. With the modern, quantitative and well-tested, theory of interstellar grain alignment now available, we have the opportunity to advance the understanding of the interstellar medium (ISM) by executing a systematic study of the UV polarization in the ISM of the Milky Way and near-by galaxies. The Polstar mission will provide the sensitivity and observing time needed to carry out such a program (probing hundreds of stars in the Milky Way and dozens of stars in the LMC/SMC), addressing questions of dust composition as a function of size and location, radiation- and magnetic-field characteristics as well as unveiling the carrier of the 2175 Å extinction feature. In addition, using high-resolution UV line spectroscopy Polstar will search for and probe the alignment of, and polarization from, aligned atoms and ions - so called “Ground State Alignment”, a potentially powerful new probe of magnetic fields in the diffuse ISM.

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A Technique for Constraining the Driving Scale of Turbulence and a Modified Chandrasekhar–fermi Method

Cited by 66 publications

References 27 publications

First Results from BISTRO: A SCUBA-2 Polarimeter Survey of the Gould Belt

First Results from BISTRO: A SCUBA-2 Polarimeter Survey of the Gould Belt

Effects of driving scale on astrophysical turbulence and a modified Chandrasekhar-Fermi method

Ultraviolet spectropolarimetry with polstar: interstellar medium science

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