Detection of submillimeter polarization in the Orion nebula

Hildebrand, R. H.; Dragovan, M.; Novak, Giles

doi:10.1086/184351

Cited by 78 publications

(67 citation statements)

References 16 publications

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“…We also note that our polarization angles agree, within the errors, with those measured by Hildebrand et al (1984) despite the different wavelengths and spatial resolutions. We therefore confirm a fairly smooth magnetic field structure where only at smaller spatial scales (< 20 , i.e., 0.04 pc) depolarization occurs towards the cores of Orion KL and South.…”

Section: Omc1supporting

confidence: 83%

“…He confirmed the relatively weak linear polarization and its position angle measured by Hildebrand et al (1984) towards the Kleinman-Low nebula (Orion KL) which is thought to be powered by an explosive event (Zapata et al 2011), while the neighboring high mass star-forming region Orion-South and the envelope of Orion KL exhibit a stronger polarization. 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.…”

Section: Omc1mentioning

confidence: 71%

“…The first detection of the polarization of the dust emission from the Orion Molecular Cloud I (OMC1) was made at λ270 µm with the Kuiper Airborne Observatory at a spatial resolution of 90 (Hildebrand et al 1984, further references to earlier attempts therein).…”

Section: Omc1mentioning

confidence: 99%

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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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Section: Omc1supporting

confidence: 83%

Section: Omc1mentioning

confidence: 71%

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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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“…Starlight appears polarized parallel with the magnetic field due to absorption effects by dust (Davis & Greenstein 1951;Hildebrand 1988). Meanwhile, thermal emission by these dust grains produce light at far-infrared and submillimetre wavelengths polarized perpendicular to the magnetic field (Hildebrand et al 1984;Novak et al 1997;Vaillancourt 2007;Alves et al 2014). This allows for the measurement of magnetic field orientations.…”

Section: Introductionmentioning

confidence: 99%

Filamentary flow and magnetic geometry in evolving cluster-forming molecular cloud clumps

Klassen

Pudritz

Kirk

2016

Mon. Not. R. Astron. Soc.

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We present an analysis of the relationship between the orientation of magnetic fields and filaments that form in 3D magnetohydrodynamic simulations of cluster-forming, turbulent molecular cloud clumps. We examine simulated cloud clumps with size scales of L ∼ 2-4 pc and densities of n ∼ 400-1000 cm −3 with Alfvén Mach numbers near unity. We simulated two cloud clumps of different masses, one in virial equilibrium, the other strongly gravitationally bound, but with the same initial turbulent velocity field and similar mass-to-flux ratio. We apply various techniques to analyze the filamentary and magnetic structure of the resulting cloud, including the DisPerSE filamentfinding algorithm in 3D. The largest structure that forms is a 1-2 parsec-long filament, with smaller connecting sub-filaments. We find that our simulated clouds, wherein magnetic forces and turbulence are comparable, coherent orientation of the magnetic field depends on the virial parameter. Subvirial clumps undergo strong gravitational collapse and magnetic field lines are dragged with the accretion flow. We see evidence of filament-aligned flow and accretion flow onto the filament in the subvirial cloud. Magnetic fields oriented more parallel in the subvirial cloud and more perpendicular in the denser, marginally bound cloud. Radiative feedback from a 16 M star forming in a cluster in one of our simulations ultimately results in the destruction of the main filament, the formation of an H ii region, and the sweeping up of magnetic fields within an expanding shell at the edges of the H ii region.

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“…In dense star-forming clouds, the polarized thermal emission from dust grains at infrared and sub-millimeter wavelengths has been shown to be a reliable technique of studying the projected magnetic field direction on the plane of sky (e.g. Hildebrand et al 1984;Hildebrand 1988;Novak et al 1997;Dotson et al 2000;Hildebrand et al 2000;Matthews et al 2001). Though the physical mechanism causing the alignment of grains with respect to the magnetic field is still an open question (see e.g.…”

mentioning

confidence: 99%

Change of Magnetic Field-Gas Alignment at the Gravity-Driven Alfvénic Transition in Molecular Clouds: Implications for Dust Polarization Observations

Chen

King

2016

ApJ

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Diffuse striations in molecular clouds are preferentially aligned with local magnetic fields whereas dense filaments tend to be perpendicular to them. When and why this transition occurs remain uncertain. To explore the physics behind this transition, we compute the histogram of relative orientation (HRO) between the density gradient and the magnetic field in 3D MHD simulations of prestellar core formation in shock-compressed regions within GMCs. We find that, in the magnetically-dominated (sub-Alfvénic) post-shock region, the gas structure is preferentially aligned with the local magnetic field. For overdense sub-regions with super-Alfvénic gas, their elongation becomes preferentially perpendicular to the local magnetic field instead. The transition occurs when self-gravitating gas gains enough kinetic energy from the gravitational acceleration to overcome the magnetic support against the cross-field contraction, which results in a power-law increase of the field strength with density. Similar results can be drawn from HROs in projected 2D maps with integrated column densities and synthetic polarized dust emission. We quantitatively analyze our simulated polarization properties, and interpret the reduced polarization fraction at high column densities as the result of increased distortion of magnetic field directions in trans-or super-Alfvénic gas. Furthermore, we introduce measures of the inclination and tangledness of the magnetic field along the line of sight as the controlling factors of the polarization fraction. Observations of the polarization fraction and angle dispersion can therefore be utilized in studying local magnetic field morphology in star-forming regions.

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Detection of submillimeter polarization in the Orion nebula

Cited by 78 publications

References 16 publications

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

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

Filamentary flow and magnetic geometry in evolving cluster-forming molecular cloud clumps

Change of Magnetic Field-Gas Alignment at the Gravity-Driven Alfvénic Transition in Molecular Clouds: Implications for Dust Polarization Observations

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