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Near-infrared polarimetric adaptive optics observations of NGC 1068: a torus created by a hydromagnetic outflow wind

Near-infrared polarimetric adaptive optics observations of NGC 1068: a torus created by a hydromagnetic outflow wind
Near-infrared polarimetric adaptive optics observations of NGC 1068: a torus created by a hydromagnetic outflow wind
We present J? and K? imaging linear polarimetric adaptive optics observations of NGC 1068 using MMT-Pol on the 6.5-m MMT. These observations allow us to study the torus from a magnetohydrodynamical (MHD) framework. In a 0.5 arcsec (30 pc) aperture at K?, we find that polarization arising from the passage of radiation from the inner edge of the torus through magnetically aligned dust grains in the clumps is the dominant polarization mechanism, with an intrinsic polarization of 7.0 ± 2.2?per?cent. This result yields a torus magnetic field strength in the range of 4–82 mG through paramagnetic alignment, and 139+11?20 mG through the Chandrasekhar–Fermi method. The measured position angle (P.A.) of polarization at K? is found to be similar to the P.A. of the obscuring dusty component at few parsec scales using infrared interferometric techniques. We show that the constant component of the magnetic field is responsible for the alignment of the dust grains, and aligned with the torus axis on to the plane of the sky. Adopting this magnetic field configuration and the physical conditions of the clumps in the MHD outflow wind model, we estimate a mass outflow rate ?0.17 M??yr?1 at 0.4 pc from the central engine for those clumps showing near-infrared dichroism. The models used were able to create the torus in a time-scale of ?105?yr with a rotational velocity of ?1228 km s?1 at 0.4 pc. We conclude that the evolution, morphology and kinematics of the torus in NGC 1068 can be explained within a MHD framework.
0035-8711
1902-1913
Lopez-Rodriguez, E.
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Packham, C.
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Jones, T.J.
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Nikutta, R.
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McMaster, L.
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Mason, R.E.
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Elvis, M.
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Shenoy, D.
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Alonso-Herrero, A.
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Ramírez, E.
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González Martín, O.
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Hoenig, S.F.
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Levenson, N.A.
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Ramos Almeida, C.
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Perlman, E.
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Lopez-Rodriguez, E.
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Packham, C.
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Jones, T.J.
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Nikutta, R.
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McMaster, L.
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Mason, R.E.
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Elvis, M.
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Shenoy, D.
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Alonso-Herrero, A.
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Ramírez, E.
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González Martín, O.
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Hoenig, S.F.
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Levenson, N.A.
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Ramos Almeida, C.
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Perlman, E.
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Lopez-Rodriguez, E., Packham, C., Jones, T.J., Nikutta, R., McMaster, L., Mason, R.E., Elvis, M., Shenoy, D., Alonso-Herrero, A., Ramírez, E., González Martín, O., Hoenig, S.F., Levenson, N.A., Ramos Almeida, C. and Perlman, E. (2015) Near-infrared polarimetric adaptive optics observations of NGC 1068: a torus created by a hydromagnetic outflow wind. Monthly Notices of the Royal Astronomical Society, 452 (2), 1902-1913. (doi:10.1093/mnras/stv1410).

Record type: Article

Abstract

We present J? and K? imaging linear polarimetric adaptive optics observations of NGC 1068 using MMT-Pol on the 6.5-m MMT. These observations allow us to study the torus from a magnetohydrodynamical (MHD) framework. In a 0.5 arcsec (30 pc) aperture at K?, we find that polarization arising from the passage of radiation from the inner edge of the torus through magnetically aligned dust grains in the clumps is the dominant polarization mechanism, with an intrinsic polarization of 7.0 ± 2.2?per?cent. This result yields a torus magnetic field strength in the range of 4–82 mG through paramagnetic alignment, and 139+11?20 mG through the Chandrasekhar–Fermi method. The measured position angle (P.A.) of polarization at K? is found to be similar to the P.A. of the obscuring dusty component at few parsec scales using infrared interferometric techniques. We show that the constant component of the magnetic field is responsible for the alignment of the dust grains, and aligned with the torus axis on to the plane of the sky. Adopting this magnetic field configuration and the physical conditions of the clumps in the MHD outflow wind model, we estimate a mass outflow rate ?0.17 M??yr?1 at 0.4 pc from the central engine for those clumps showing near-infrared dichroism. The models used were able to create the torus in a time-scale of ?105?yr with a rotational velocity of ?1228 km s?1 at 0.4 pc. We conclude that the evolution, morphology and kinematics of the torus in NGC 1068 can be explained within a MHD framework.

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Accepted/In Press date: 23 June 2015
e-pub ahead of print date: 21 July 2015
Published date: 11 September 2015
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 402382
URI: http://eprints.soton.ac.uk/id/eprint/402382
ISSN: 0035-8711
PURE UUID: b03d8a15-0caf-493f-b18f-d06c215ff992

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Date deposited: 07 Nov 2016 16:26
Last modified: 21 Nov 2021 04:19

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Contributors

Author: E. Lopez-Rodriguez
Author: C. Packham
Author: T.J. Jones
Author: R. Nikutta
Author: L. McMaster
Author: R.E. Mason
Author: M. Elvis
Author: D. Shenoy
Author: A. Alonso-Herrero
Author: E. Ramírez
Author: O. González Martín
Author: S.F. Hoenig
Author: N.A. Levenson
Author: C. Ramos Almeida
Author: E. Perlman

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