Effects of grain alignment efficiency on synthetic dust polarization observations of molecular clouds

King, Patrick; Chen, Che-Yu; Fissel, Laura M.; Li, Zhi-Yun

doi:10.1093/mnras/stz2628

Cited by 18 publications

(20 citation statements)

References 47 publications

(93 reference statements)

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“…molecular cloud complex Vela C (Fissel et al 2016). The suggested possible explanations for this trend are due to: (1) the loss of the grain alignment because of the grain growth (Bethell et al 2007;Brauer et al 2016) or scattering and absorption of photons at high density (King et al 2018(King et al , 2019; (2) the optical depth effect (Dowell 1997;Hildebrand et al 1999); or (3) the unresolved complex B-field structures along the line of sight. It is, however, beyond the scope of this paper to constrain them using only these data.…”

Section: Polarization Propertiesmentioning

confidence: 99%

The JCMT BISTRO Survey: An 850/450 μm Polarization Study of NGC 2071IR in Orion B

Lyo¹,

Kim²,

Sadavoy³

et al. 2021

ApJ

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We present the results of simultaneous 450 μm and 850 μm polarization observations toward the massive starforming region NGC 2071IR, a target of the BISTRO (B-fields in STar-forming Region Observations) Survey, using the POL-2 polarimeter and SCUBA-2 camera mounted on the James Clerk Maxwell Telescope. We find a pinched magnetic field morphology in the central dense core region, which could be due to a rotating toroidal disklike structure and a bipolar outflow originating from the central young stellar object IRS 3. Using the modified Davis-Chandrasekhar-Fermi method, we obtain a plane-of-sky magnetic field strength of 563 ± 421 μG in the central ∼0.12 pc region from 850 μm polarization data. The corresponding magnetic energy density of 2.04 × 10 −8 erg cm −3 is comparable to the turbulent and gravitational energy densities in the region. We find that 85 NAOJ Fellow.

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Section: Polarization Propertiesmentioning

confidence: 99%

The JCMT BISTRO Survey: An 850/450 μm Polarization Study of NGC 2071IR in Orion B

Lyo¹,

Kim²,

Sadavoy³

et al. 2021

ApJ

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“…King et al (2018) highlighted the importance of properly treating grain alignment physics in modeling synthetic observations. Corrections for mimicking RAT alignment were later investigated in King et al (2019) without invoking the full complexity of RAT physics.…”

Section: Origin Of Dust Polarizationmentioning

confidence: 99%

Linear dust polarization during the embedded phase of protostar formation

Küffmeier

Reißl

Wolf

et al. 2020

A&A

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Context. Measuring polarization from thermal dust emission can provide important constraints on the magnetic field structure around embedded protostars. However, interpreting the observations is challenging without models that consistently account for both the complexity of the turbulent protostellar birth environment and polarization mechanisms. Aims. We aim to provide a better understanding of dust polarization maps of embedded protostars with a focus on bridge-like structures such as the structure observed toward the protostellar multiple system IRAS 16293–2422 by comparing synthetic polarization maps of thermal reemission with recent observations. Methods. We analyzed the magnetic field morphology and properties associated with the formation of a protostellar multiple based on ideal magnetohydrodynamic 3D zoom-in simulations carried out with the RAMSES code. To compare the models with observations, we postprocessed a snapshot of a bridge-like structure that is associated with a forming triple star system with the radiative transfer code POLARIS and produced multiwavelength dust polarization maps. Results. The typical density in the most prominent bridge of our sample is about 10−16 g cm−3, and the magnetic field strength in the bridge is about 1 to 2 mG. Inside the bridge, the magnetic field structure has an elongated toroidal morphology, and the dust polarization maps trace the complex morphology. In contrast, the magnetic field strength associated with the launching of asymmetric bipolar outflows is significantly more magnetized (~100 mG). At λ = 1.3 mm, and the orientation of the grains in the bridge is very similar for the case accounting for radiative alignment torques (RATs) compared to perfect alignment with magnetic field lines. However, the polarization fraction in the bridge is three times smaller for the RAT scenario than when perfect alignment is assumed. At shorter wavelength (λ ≲ 200 μm), however, dust polarization does not trace the magnetic field because other effects such as self-scattering and dichroic extinction dominate the orientation of the polarization. Conclusions. Compared to the launching region of protostellar outflows, the magnetic field in bridge-like structures is weak. Synthetic dust polarization maps of ALMA Bands 6 and 7 (1.3 mm and 870 μm, respectively) can be used as a tracer of the complex morphology of elongated toroidal magnetic fields associated with bridges.

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“…In more recent work employing MHD simulations, King et al (2018) and Seifried et al (2019) find that the ordered and random components are more complicated than modeled by Jones et al (1992). While Jones et al (2015a) argued that a slope of α = −1 indicated complete loss of grain alignment due solely to loss of radiation that aligns grains by radiative torques (Lazarian & Hoang 2007;Andersson et al 2015), King et al (2019) find that including a dependency on local density for grain alignment efficiency can help explain these trends seen in large molecular clouds.…”

Section: Polarization -Intensity Relationmentioning

confidence: 99%

HAWC+ Far-Infrared Observations of the Magnetic Field Geometry in M51 and NGC 891

Jones,

Kim,

Dowell

et al. 2020

Preprint

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SOFIA HAWC+ polarimetry at 154 µm is reported for the face-on galaxy M51 and the edge-on galaxy NGC 891. For M51, the polarization vectors generally follow the spiral pattern defined by the molecular gas distribution, the far-infrared (FIR) intensity contours, and other tracers of star formation. The fractional polarization is much lower in the FIR-bright central regions than in the outer regions, and we rule out loss of grain alignment and variations in magnetic field strength as causes. When compared with existing synchrotron observations, which sample different regions with different weighting, we find the net position angles are strongly correlated, the fractional polarizations are moderately correlated, but the polarized intensities are uncorrelated. We argue that the low fractional polarization in the central regions must be due to significant numbers of highly turbulent segments across the beam and along lines of sight in the beam in the central 3 kpc of M51. For NGC 891, the FIR polarization vectors within an intensity contour of 1500 MJy sr −1 are oriented very close to the plane of the galaxy. The FIR polarimetry is probably sampling the magnetic field geometry in NGC 891 much deeper into the disk than is possible with NIR polarimetry and radio synchrotron

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Effects of grain alignment efficiency on synthetic dust polarization observations of molecular clouds

Cited by 18 publications

References 47 publications

The JCMT BISTRO Survey: An 850/450 μm Polarization Study of NGC 2071IR in Orion B

The JCMT BISTRO Survey: An 850/450 μm Polarization Study of NGC 2071IR in Orion B

Linear dust polarization during the embedded phase of protostar formation

HAWC+ Far-Infrared Observations of the Magnetic Field Geometry in M51 and NGC 891

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