Anisotropy in the angular broadening of Sagittarius A* at the Galactic center

Farhad Yusef-Zadeh; William Cotton; Mark Wardle; Fulvio Melia; Douglas A. Roberts

doi:10.1086/187575

Anisotropy in the angular broadening of Sagittarius A* at the Galactic center

Farhad Yusef-Zadeh, William Cotton, Mark Wardle, Fulvio Melia, Douglas A. Roberts

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40 Scopus citations

Abstract

We present the results of a λ = 20 cm VLA² observation of the compact Galactic center radio source Sgr A*. The scatter-broadened image is elongated in the east-west direction, with an axial ratio of 0.56 ± 0.22 and a position angle of 82° ± 1°.8. A similar shape and orientation has been found previously at shorter wave-lengths using VLBI and VLBA. Both the major and minor axes follow the λ² law appropriate for scattering by turbulence in the intervening medium. We argue that the scattering occurs in thin ionized surface layers of molecular clouds lying in the central 100 pc of the Galaxy. The ionized regions are characterized by electron densities of 10⁴ cm^-3 and milligauss magnetic field strengths, and are responsible for the diffuse free-free emission and the Faraday rotation in the region.

Original language	English (US)
Pages (from-to)	L63-L66
Journal	Astrophysical Journal
Volume	434
Issue number	2 PART 2
DOIs	https://doi.org/10.1086/187575
State	Published - Oct 20 1994

Keywords

Galaxies: ISM
Galaxy: center
ISM: individual (Sagittarius A*, IRS 16)

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.1086/187575

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title = "Anisotropy in the angular broadening of Sagittarius A* at the Galactic center",

abstract = "We present the results of a λ = 20 cm VLA2 observation of the compact Galactic center radio source Sgr A*. The scatter-broadened image is elongated in the east-west direction, with an axial ratio of 0.56 ± 0.22 and a position angle of 82° ± 1°.8. A similar shape and orientation has been found previously at shorter wave-lengths using VLBI and VLBA. Both the major and minor axes follow the λ2 law appropriate for scattering by turbulence in the intervening medium. We argue that the scattering occurs in thin ionized surface layers of molecular clouds lying in the central 100 pc of the Galaxy. The ionized regions are characterized by electron densities of 104 cm-3 and milligauss magnetic field strengths, and are responsible for the diffuse free-free emission and the Faraday rotation in the region.",

keywords = "Galaxies: ISM, Galaxy: center, ISM: individual (Sagittarius A*, IRS 16)",

author = "Farhad Yusef-Zadeh and William Cotton and Mark Wardle and Fulvio Melia and Roberts, {Douglas A.}",

year = "1994",

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T1 - Anisotropy in the angular broadening of Sagittarius A* at the Galactic center

AU - Yusef-Zadeh, Farhad

AU - Cotton, William

AU - Wardle, Mark

AU - Melia, Fulvio

AU - Roberts, Douglas A.

PY - 1994/10/20

Y1 - 1994/10/20

N2 - We present the results of a λ = 20 cm VLA2 observation of the compact Galactic center radio source Sgr A*. The scatter-broadened image is elongated in the east-west direction, with an axial ratio of 0.56 ± 0.22 and a position angle of 82° ± 1°.8. A similar shape and orientation has been found previously at shorter wave-lengths using VLBI and VLBA. Both the major and minor axes follow the λ2 law appropriate for scattering by turbulence in the intervening medium. We argue that the scattering occurs in thin ionized surface layers of molecular clouds lying in the central 100 pc of the Galaxy. The ionized regions are characterized by electron densities of 104 cm-3 and milligauss magnetic field strengths, and are responsible for the diffuse free-free emission and the Faraday rotation in the region.

AB - We present the results of a λ = 20 cm VLA2 observation of the compact Galactic center radio source Sgr A*. The scatter-broadened image is elongated in the east-west direction, with an axial ratio of 0.56 ± 0.22 and a position angle of 82° ± 1°.8. A similar shape and orientation has been found previously at shorter wave-lengths using VLBI and VLBA. Both the major and minor axes follow the λ2 law appropriate for scattering by turbulence in the intervening medium. We argue that the scattering occurs in thin ionized surface layers of molecular clouds lying in the central 100 pc of the Galaxy. The ionized regions are characterized by electron densities of 104 cm-3 and milligauss magnetic field strengths, and are responsible for the diffuse free-free emission and the Faraday rotation in the region.

KW - Galaxies: ISM

KW - Galaxy: center

KW - ISM: individual (Sagittarius A, IRS 16)

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DO - 10.1086/187575

M3 - Article

AN - SCOPUS:12044254976

SN - 0004-637X

VL - 434

SP - L63-L66

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 2 PART 2

ER -

Anisotropy in the angular broadening of Sagittarius A* at the Galactic center

Abstract

Keywords

ASJC Scopus subject areas

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