New Results on the Submillimeter Polarization Spectrum of the Orion Molecular Cloud

Vaillancourt, John E.; Dowell, C. D.; Hildebrand, R. H.; Kirby, Larry; Krejny, M.; Li, Hua Bai; Novak, Giles; Houde, Martin; Shinnaga, Hiroko; Attard, Michael

doi:10.1086/589152

Cited by 56 publications

(89 citation statements)

References 30 publications

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“…Indeed, this is why weak fields are expected to follow cloud rotation and turbulence, whilst strong fields will channel turbulence and suppress cloud rotation (Figure 2). Moving toward small scales, however, the MHD induction equation also suggests decoupling between turbulent eddies and B fields (when the magnetic Reynolds number, R M , is approximately below unity; Li and Houde 2008). This may help to solve the magnetic braking catastrophe, if this decoupling scale, L , is comparable to the scales of protostellar discs (a few hundred AU) and turbulence at this scale is the main energy source of disc angular momentum.…”

Section: Observation X: Decoupling Between B Fields and Turbulence Amentioning

confidence: 99%

“…By setting R M (the ratio between the advection term and diffusion terms of the induction equation) equal to unity, it can be shown that (Li and Houde 2008): B 2 pos ≈ 4πn i µv i V n L , where B pos , n i , v i and µ are, respectively, the plane-of-sky B-field strength, the ion density, the collision rate between an ion and the neutrals, and the reduced mass for such collisions. V n is the neutral turbulent velocity at L .…”

Section: Observation X: Decoupling Between B Fields and Turbulence Amentioning

confidence: 99%

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The Link Between Magnetic Fields and Cloud/Star Formation

Li¹,

Goodman

Sridharan³

et al. 2014

Protostars and Planets VI

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The question whether magnetic fields play an important role in the processes of molecular cloud and star formation has been debated for decades. Recent observations have revealed a simple picture that may help illuminate these questions: magnetic fields have a tendency to preserve their orientation at all scales that have been probed -from 100-pc scale inter-cloud media down to sub-pc scale cloud cores. This ordered morphology has implications for the way in which self-gravity and turbulence interact with magnetic fields: both gravitational contraction and turbulent velocities should be anisotropic, due to the influence of dynamically important magnetic fields. Such anisotropy is now observed. Here we review these recent observations and discuss how they can improve our understanding of cloud/star formation.

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Section: Observation X: Decoupling Between B Fields and Turbulence Amentioning

confidence: 99%

Section: Observation X: Decoupling Between B Fields and Turbulence Amentioning

confidence: 99%

The Link Between Magnetic Fields and Cloud/Star Formation

Li¹,

Goodman

Sridharan³

et al. 2014

Protostars and Planets VI

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“…Schleuning (1998) explains the depolarization in Orion KL by the rising dust opacity towards the far-infrared, while the low polarization in the Orion Bar, a photon-dominated region seen edge-on (Tielens & Hollenbach 1985), is attributed to a magnetic field pointing to the observer. Vaillancourt et al (2008) studied the polarization spectrum of OMC-1 and conclude that a polarization minimum occurs between λ100 µm and λ350 µm while Houde et al (2004), investigating the large scale structure of the magnetic field in Orion A, confirmed the relatively smooth polarization angle structure towards OMC1 and interprete the weak polarization levels in the Orion bar with the lower dust temperature in that region.…”

Section: Omc1mentioning

confidence: 87%

Submillimeter polarimetry with PolKa, a reflection-type modulator for the APEX telescope

Wiesemeyer

Hezareh

Kreysa

et al. 2014

2014 39th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

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Imaging polarimetry is an important tool for the study of cosmic magnetic fields. In our Galaxy, polarization levels of a few up to ∼10% are measured in the submillimeter dust emission from molecular clouds and in the synchrotron emission from supernova remnants. Only few techniques exist to image the distribution of polarization angles, as a means of tracing the plane-of-sky projection of the magnetic field orientation. At submillimeter wavelengths, polarization is either measured as the differential total power of polarization-sensitive bolometer elements, or by modulating the polarization of the signal. Bolometer arrays such as LABOCA at the APEX telescope are used to observe the continuum emission from fields as large as ∼ 0.• 2 in diameter. Here we present PolKa, a polarimeter for LABOCA with a reflection-type waveplate of at least 90% efficiency.The modulation efficiency depends mainly on the sampling and on the angular velocity of the waveplate. For the data analysis the concept of generalized synchronous demodulation is introduced. The instrumental polarization towards a point source is at the level of ∼ 0.1%, increasing to a few percent at the −10db contour of the main beam. A method to correct for its effect in observations of extended sources is presented. Our map of the polarized synchrotron emission from the Crab nebula is in agreement with structures observed at radio and optical wavelengths. The linear polarization measured in OMC1 agrees with results from previous studies, while the high sensitivity of LABOCA enables us to also map the polarized emission of the Orion Bar, a prototypical photon-dominated region.

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“…One of the diffuse foregrounds contaminating the CMB signal is thermal emission by diffuse interstellar dust. Because interstellar polarization of starlight is commonly seen in the visible from differential extinction by aspherical dust particles that are aligned with respect to the Galactic magnetic field (Hall 1949;Hiltner 1949;Davis & Greenstein 1951), it was predicted that the thermal emission from these grains would be polarized (Stein 1966) and indeed this is the case (Hildebrand et al 1999;Benoît et al 2004;Kogut et al 2007;Vaillancourt et al 2008;Bierman et al 2011;Planck Collaboration Int. XIX 2015 and references therein).…”

Section: Introductionmentioning

confidence: 99%

“…On high column density lines of sight in the Galactic plane and in dense molecular clouds, even when polarization data in the visible are available, the interpretation of the visible and submillimetre polarization is further complicated by beam dilution; distortions in the magnetic field topology; changes in the degree of alignment along the line of sight; grain evolution; and ranges of grain temperature and optical depth that affect which grains dominate the polarized emission in various parts of the submillimetre spectrum (e.g., Hildebrand et al 1999;Vaillancourt 2007;Vaillancourt et al 2008;Bierman et al 2011;Vaillancourt & Matthews 2012). Such complex regions are deliberately not considered here.…”

Section: Introductionmentioning

confidence: 99%

Planckintermediate results. XXI. Comparison of polarized thermal emission from Galactic dust at 353 GHz with interstellar polarization in the visible

Ade

Aghanim

Alina

et al. 2015

A&A

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The Planck survey provides unprecedented full-sky coverage of the submillimetre polarized emission from Galactic dust. In addition to the information on the direction of the Galactic magnetic field, this also brings new constraints on the properties of dust. The dust grains that emit the radiation seen by Planck in the submillimetre also extinguish and polarize starlight in the visible. Comparison of the polarization of the emission and of the interstellar polarization on selected lines of sight probed by stars provides unique new diagnostics of the emission and light scattering properties of dust, and therefore of the important dust model parameters, composition, size, and shape. Using ancillary catalogues of interstellar polarization and extinction of starlight, we obtain the degree of polarization, p V , and the optical depth in the V band to the star, τ V . Toward these stars we measure the submillimetre polarized intensity, P S , and total intensity, I S , in the Planck 353 GHz channel. We compare the column density measure in the visible, E(B − V), with that inferred from the Planck product map of the submillimetre dust optical depth and compare the polarization direction (position angle) in the visible with that in the submillimetre. For those lines of sight through the diffuse interstellar medium with comparable values of the estimated column density and polarization directions close to orthogonal, we correlate properties in the submillimetre and visible to find two ratios, R S/V = (P S /I S )/(p V /τ V ) and R P/p = P S /p V , the latter focusing directly on the polarization properties of the aligned grain population alone. We find R S/V = 4.2, with statistical and systematic uncertainties 0.2 and 0.3, respectively, and R P/p = 5.4 MJy sr −1 , with uncertainties 0.2 and 0.3 MJy sr −1 , respectively. Our estimate of R S/V is compatible with predictions based on a range of polarizing dust models that have been developed for the diffuse interstellar medium. This estimate provides new empirical validation of many of the common underlying assumptions of the models, but is not yet very discriminating among them. However, our estimate of R P/p is not compatible with predictions, which are too low by a factor of about 2.5. This more discriminating diagnostic, R P/p , indicates that changes to the optical properties in the models of the aligned grain population are required. These new diagnostics, together with the spectral dependence in the submillimetre from Planck, will be important for constraining and understanding the full complexity of the grain models, and for interpreting the Planck thermal dust polarization and refinement of the separation of this contamination of the cosmic microwave background.Key words. polarization -dust, extinction -ISM: clouds -ISM: magnetic fields -submillimeter: ISM Appendices are available in electronic form at

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New Results on the Submillimeter Polarization Spectrum of the Orion Molecular Cloud

Cited by 56 publications

References 30 publications

The Link Between Magnetic Fields and Cloud/Star Formation

The Link Between Magnetic Fields and Cloud/Star Formation

Submillimeter polarimetry with PolKa, a reflection-type modulator for the APEX telescope

Planckintermediate results. XXI. Comparison of polarized thermal emission from Galactic dust at 353 GHz with interstellar polarization in the visible

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