Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds

P.A.R Ade; N. Aghanim; M.I.R. Alves; L. Arnaud; D. Arzoumanian; M. Ashdown; J. Aumont; C. Baccigalupi; A.J. Banday; R.B. Barreiro; N. Bartolo; Per Rex Christensen; Anne Mette Frejsel; Pavel Nasselski; Igor Dmitrievich Novikov; Hans Ulrik Nørgaard-Nielsen

doi:10.1051/0004-6361/201525896

Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds

P.A.R Ade, N. Aghanim, M.I.R. Alves, L. Arnaud, D. Arzoumanian, M. Ashdown, J. Aumont, C. Baccigalupi, A.J. Banday, R.B. Barreiro, N. Bartolo, Per Rex Christensen, Anne Mette Frejsel, Pavel Nasselski, Igor Dmitrievich Novikov, Hans Ulrik Nørgaard-Nielsen

Theoretical high energy, astroparticle and gravitational physics

74 Citations (Scopus)

Abstract

Within ten nearby (d < 450 pc) Gould belt molecular clouds we evaluate statistically the relative orientation between the magnetic field projected on the plane of sky, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the gas column density structures, quantified by the gradient of the column density, N_H. The selected regions, covering several degrees in size, are analysed at an effective angular resolution of 10′ FWHM, thus sampling physical scales from 0.4 to 40 pc in the nearest cloud. The column densities in the selected regions range from N_H ≈ 10²¹ to 10²³ cm^-2, and hence they correspond to the bulk of the molecular clouds. The relative orientation is evaluated pixel by pixel and analysed in bins of column density using the novel statistical tool called "histogram of relative orientations". Throughout this study, we assume that the polarized emission observed by Planck at 353 GHz is representative of the projected morphology of the magnetic field in each region, i.e., we assume a constant dust grain alignment efficiency, independent of the local environment. Within most clouds we find that the relative orientation changes progressively with increasing N_H, from mostly parallel or having no preferred orientation to mostly perpendicular. In simulations of magnetohydrodynamic turbulence in molecular clouds this trend in relative orientation is a signature of Alfvénic or sub-Alfvénic turbulence, implying that the magnetic field is significant for the gas dynamics at the scales probed by Planck. We compare the deduced magnetic field strength with estimates we obtain from other methods and discuss the implications of the Planck observations for the general picture of molecular cloud formation and evolution.

Original language	English
Article number	A138
Journal	Astronomy & Astrophysics
Volume	538
ISSN	0004-6361
DOIs	https://doi.org/10.1051/0004-6361/201525896
Publication status	Published - 1 Feb 2016

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Ade, P. A. R., Aghanim, N., Alves, M. I. R., Arnaud, L., Arzoumanian, D., Ashdown, M., Aumont, J., Baccigalupi, C., Banday, A. J., Barreiro, R. B., Bartolo, N., Christensen, P. R., Frejsel, A. M., Nasselski, P., Novikov, I. D., & Nørgaard-Nielsen, H. U. (2016). Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds. Astronomy & Astrophysics, 538, Article A138. https://doi.org/10.1051/0004-6361/201525896

Ade, PAR, Aghanim, N, Alves, MIR, Arnaud, L, Arzoumanian, D, Ashdown, M, Aumont, J, Baccigalupi, C, Banday, AJ, Barreiro, RB, Bartolo, N, Christensen, PR, Frejsel, AM, Nasselski, P, Novikov, ID & Nørgaard-Nielsen, HU 2016, 'Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds', Astronomy & Astrophysics, vol. 538, A138. https://doi.org/10.1051/0004-6361/201525896

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title = "Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds",

abstract = "Within ten nearby (d < 450 pc) Gould belt molecular clouds we evaluate statistically the relative orientation between the magnetic field projected on the plane of sky, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the gas column density structures, quantified by the gradient of the column density, NH. The selected regions, covering several degrees in size, are analysed at an effective angular resolution of 10′ FWHM, thus sampling physical scales from 0.4 to 40 pc in the nearest cloud. The column densities in the selected regions range from NH ≈ 1021 to 1023 cm-2, and hence they correspond to the bulk of the molecular clouds. The relative orientation is evaluated pixel by pixel and analysed in bins of column density using the novel statistical tool called {"}histogram of relative orientations{"}. Throughout this study, we assume that the polarized emission observed by Planck at 353 GHz is representative of the projected morphology of the magnetic field in each region, i.e., we assume a constant dust grain alignment efficiency, independent of the local environment. Within most clouds we find that the relative orientation changes progressively with increasing NH, from mostly parallel or having no preferred orientation to mostly perpendicular. In simulations of magnetohydrodynamic turbulence in molecular clouds this trend in relative orientation is a signature of Alfv{\'e}nic or sub-Alfv{\'e}nic turbulence, implying that the magnetic field is significant for the gas dynamics at the scales probed by Planck. We compare the deduced magnetic field strength with estimates we obtain from other methods and discuss the implications of the Planck observations for the general picture of molecular cloud formation and evolution.",

author = "P.A.R Ade and N. Aghanim and M.I.R. Alves and L. Arnaud and D. Arzoumanian and M. Ashdown and J. Aumont and C. Baccigalupi and A.J. Banday and R.B. Barreiro and N. Bartolo and Christensen, {Per Rex} and Frejsel, {Anne Mette} and Pavel Nasselski and Novikov, {Igor Dmitrievich} and N{\o}rgaard-Nielsen, {Hans Ulrik}",

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T1 - Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds

AU - Ade, P.A.R

AU - Aghanim, N.

AU - Alves, M.I.R.

AU - Arnaud, L.

AU - Arzoumanian, D.

AU - Ashdown, M.

AU - Aumont, J.

AU - Baccigalupi, C.

AU - Banday, A.J.

AU - Barreiro, R.B.

AU - Bartolo, N.

AU - Christensen, Per Rex

AU - Frejsel, Anne Mette

AU - Nasselski, Pavel

AU - Novikov, Igor Dmitrievich

AU - Nørgaard-Nielsen, Hans Ulrik

PY - 2016/2/1

Y1 - 2016/2/1

N2 - Within ten nearby (d < 450 pc) Gould belt molecular clouds we evaluate statistically the relative orientation between the magnetic field projected on the plane of sky, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the gas column density structures, quantified by the gradient of the column density, NH. The selected regions, covering several degrees in size, are analysed at an effective angular resolution of 10′ FWHM, thus sampling physical scales from 0.4 to 40 pc in the nearest cloud. The column densities in the selected regions range from NH ≈ 1021 to 1023 cm-2, and hence they correspond to the bulk of the molecular clouds. The relative orientation is evaluated pixel by pixel and analysed in bins of column density using the novel statistical tool called "histogram of relative orientations". Throughout this study, we assume that the polarized emission observed by Planck at 353 GHz is representative of the projected morphology of the magnetic field in each region, i.e., we assume a constant dust grain alignment efficiency, independent of the local environment. Within most clouds we find that the relative orientation changes progressively with increasing NH, from mostly parallel or having no preferred orientation to mostly perpendicular. In simulations of magnetohydrodynamic turbulence in molecular clouds this trend in relative orientation is a signature of Alfvénic or sub-Alfvénic turbulence, implying that the magnetic field is significant for the gas dynamics at the scales probed by Planck. We compare the deduced magnetic field strength with estimates we obtain from other methods and discuss the implications of the Planck observations for the general picture of molecular cloud formation and evolution.

AB - Within ten nearby (d < 450 pc) Gould belt molecular clouds we evaluate statistically the relative orientation between the magnetic field projected on the plane of sky, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the gas column density structures, quantified by the gradient of the column density, NH. The selected regions, covering several degrees in size, are analysed at an effective angular resolution of 10′ FWHM, thus sampling physical scales from 0.4 to 40 pc in the nearest cloud. The column densities in the selected regions range from NH ≈ 1021 to 1023 cm-2, and hence they correspond to the bulk of the molecular clouds. The relative orientation is evaluated pixel by pixel and analysed in bins of column density using the novel statistical tool called "histogram of relative orientations". Throughout this study, we assume that the polarized emission observed by Planck at 353 GHz is representative of the projected morphology of the magnetic field in each region, i.e., we assume a constant dust grain alignment efficiency, independent of the local environment. Within most clouds we find that the relative orientation changes progressively with increasing NH, from mostly parallel or having no preferred orientation to mostly perpendicular. In simulations of magnetohydrodynamic turbulence in molecular clouds this trend in relative orientation is a signature of Alfvénic or sub-Alfvénic turbulence, implying that the magnetic field is significant for the gas dynamics at the scales probed by Planck. We compare the deduced magnetic field strength with estimates we obtain from other methods and discuss the implications of the Planck observations for the general picture of molecular cloud formation and evolution.

U2 - 10.1051/0004-6361/201525896

DO - 10.1051/0004-6361/201525896

M3 - Journal article

SN - 0004-6361

VL - 538

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

M1 - A138

ER -

Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds

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