Magnetic Fields in Star‐forming Molecular Clouds. IV. Polarimetry of the Filamentary NGC 2068 Cloud in Orion B

Matthews, Brenda C.; Wilson, C. D.

doi:10.1086/339915

Cited by 17 publications

(10 citation statements)

References 33 publications

(53 reference statements)

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“…This leads to the theory that the emission in the west originates from gas and dust in front of the nebula, with the rest of the emission originates from deeper in the cloud, behind the nebula. This theory is supported by polarimetry analysis carried out by Matthews and Wilson (2002), who in addition, argue that while the emission originates from two distinct regions, these two regions are most likely not completely spatially separated, implying that the filament does not lie in the plane of the sky. Instead, the dust filament is thought to be twisted with the western edge lying in the foreground of the optical reflection nebula while the eastern edge lies behind it.…”

Section: Velocity Structure and Kinematicsmentioning

confidence: 74%

The structure and kinematics of dense gas in NGC 2068

Walker-Smith¹,

Richer

Buckle

et al. 2013

Monthly Notices of the Royal Astronomical Society

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We have carried out a survey of the NGC 2068 region in the Orion B molecular cloud using HARP on the JCMT, in the 13 CO and C 18 O (J = 3 -2) and H 13 CO + (J = 4 -3) lines. We used 13 CO to map the outflows in the region, and matched them with previously defined SCUBA cores. We decomposed the C 18 O and H 13 CO + into Gaussian clumps, finding 26 and 8 clumps respectively. The average deconvolved radii of these clumps is 6200 ± 2000 AU and 3600 ± 900 AU for C 18 O and H 13 CO + respectively. We have also calculated virial and gas masses for these clumps, and hence determined how bound they are. We find that the C 18 O clumps are more bound than the H 13 CO + clumps (average gas mass to virial mass ratio of 4.9 compared to 1.4). We measure clump internal velocity dispersions of 0.28 ± 0.02 km s −1 and 0.27±0.04 km s −1 for C 18 O and H 13 CO + respectively, although the H 13 CO + values are heavily weighted by a majority of the clumps being protostellar, and hence having intrinsically greater linewidths. We suggest that the starless clumps correspond to local turbulence minima, and we find that our clumps are consistent with formation by gravoturbulent fragmentation. We also calculate inter-clump velocity dispersions of 0.39±0.05 km s −1 and 0.28±0.08 km s −1 for C 18 O and H 13 CO + respectively. The velocity dispersions (both internal and external) for our clumps match results from numerical simulations of decaying turbulence in a molecular cloud. However, there is still insufficient evidence to conclusively determine the type of turbulence and timescale of star formation, due to the small size of our sample.

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Section: Velocity Structure and Kinematicsmentioning

confidence: 74%

The structure and kinematics of dense gas in NGC 2068

Walker-Smith¹,

Richer

Buckle

et al. 2013

Monthly Notices of the Royal Astronomical Society

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“…What does this polarization fraction tell us about the properties of the dust in Cas A? Average polarization fractions in typical interstellar and molecular clouds are of the order 2–7 per cent (Hildebrand et al 2000; Matthews & Wilson 2002; Curran & Chrysostomou 2007) though some clouds have values as high as 15–20 per cent (Benoît et al 2004). We are unaware of any measurements as high as those quoted here, which suggests that either the dust or the alignment mechanisms in Cas A differ – perhaps unsurprisingly – from those in the general ISM.…”

Section: Discussionmentioning

confidence: 99%

Cassiopeia A: dust factory revealed via submillimetre polarimetry

Dunne

Maddox

Ivison

et al. 2009

Monthly Notices of the Royal Astronomical Society

124

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If Type-II supernovae - the evolutionary end points of short-lived, massive stars - produce a significant quantity of dust (>0.1 M_sun) then they can explain the rest-frame far-infrared emission seen in galaxies and quasars in the first Gyr of the Universe. Submillimetre observations of the Galactic supernova remnant, Cas A, provided the first observational evidence for the formation of significant quantities of dust in Type-II supernovae. In this paper we present new data which show that the submm emission from Cas A is polarised at a level significantly higher than that of its synchrotron emission. The orientation is consistent with that of the magnetic field in Cas A, implying that the polarised submm emission is associated with the remnant. No known mechanism would vary the synchrotron polarisation in this way and so we attribute the excess polarised submm flux to cold dust within the remnant, providing fresh evidence that cosmic dust can form rapidly. This is supported by the presence of both polarised and unpolarised dust emission in the north of the remnant, where there is no contamination from foreground molecular clouds. The inferred dust polarisation fraction is unprecedented (f_pol ~ 30%) which, coupled with the brief timescale available for grain alignment (<300 yr), suggests that supernova dust differs from that seen in other Galactic sources (where f_pol=2-7%), or that a highly efficient grain alignment process must operate in the environment of a supernova remnant.Comment: In press at MNRAS, 10 pages, print in colou

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“…Regarding the effect of magnetic helicity on dust polarization power spectra, our first intuition is conservative within the interpretation frame of the correlation between density filaments and the magnetic field in the ISM. The existence of helical magnetic fields wrapped around the main axis of molecular filaments has been observed (Bally et al 1987;Matthews & Wilson 2002;Poidevin et al 2011;Tahani et al 2018), and is suggested to regulate the dynamics of such clouds against gravitational fragmentation (Fiege & Pudritz 2000;Toci & Galli 2015).…”

Section: Introductionmentioning

confidence: 99%

Is there a left-handed magnetic field in the solar neighborhood?

Bracco

Candelaresi

Sordo

et al. 2019

A&A

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Context. The analysis of the full-sky Planck polarization data at 850 μm revealed unexpected properties of the E- and B-mode power spectra of dust emission in the interstellar medium (ISM). The positive cross-correlations over a wide range of angular scales between the total dust intensity, T, and both E and (most of all) B modes has raised new questions about the physical mechanisms that affect dust polarization, such as the Galactic magnetic field structure. This is key both to better understanding ISM dynamics and to accurately describing Galactic foregrounds to the polarization of the cosmic microwave background (CMB). In particular, in the quest to find primordial B modes of the CMB, the observed positive cross-correlation between T and B for interstellar dust requires further investigation towards parity-violating processes in the ISM. Aims. In this theoretical paper we investigate the possibility that the observed cross-correlations in the dust polarization power spectra, and specifically the one between T and B, can be related to a parity-odd quantity in the ISM such as the magnetic helicity. Methods. We produce synthetic dust polarization data, derived from 3D analytical toy models of density structures and helical magnetic fields, to compare with the E and B modes of observations. We present several models. The first is an ideal fully helical isotropic case, such as the Arnold-Beltrami-Childress field. Second, following the nowadays favored interpretation of the T–E signal in terms of the observed alignment between the magnetic field morphology and the filamentary density structure of the diffuse ISM, we design models for helical magnetic fields wrapped around cylindrical interstellar filaments. Lastly, focusing on the observed T–B correlation, we propose a new line of interpretation of the Planck observations advocating the presence of a large-scale helical component of the Galactic magnetic field in the solar neighborhood. Results. Our analysis shows that: I) the sign of magnetic helicity does not affect E and B modes for isotropic magnetic-field configurations; II) helical magnetic fields threading interstellar filaments cannot reproduce the Planck results; and III) a weak helical left-handed magnetic field structure in the solar neighborhood may explain the T–B correlation seen in the Planck data. Such a magnetic-field configuration would also account for the observed large-scale T–E correlation. Conclusions. This work suggests a new perspective for the interpretation of the dust polarization power spectra that supports the imprint of a large-scale structure of the Galactic magnetic field in the solar neighborhood.

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Magnetic Fields in Star‐forming Molecular Clouds. IV. Polarimetry of the Filamentary NGC 2068 Cloud in Orion B

Cited by 17 publications

References 33 publications

The structure and kinematics of dense gas in NGC 2068

The structure and kinematics of dense gas in NGC 2068

Cassiopeia A: dust factory revealed via submillimetre polarimetry

Is there a left-handed magnetic field in the solar neighborhood?

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