Polarimetric Observations of the Masers in NGC 4258: An Upper Limit on the Large-Scale Magnetic Field 0.2 pc from the Central Engine

Abstract

We report VLA 1 sigma upper limits of 1.5% and 3% on the intrinsic circular and linear fractional polarizations, respectively, of the water vapor maser emission 0.2 pc from the central engine of NGC 4258. A corresponding 0.5% upper limit on any Zeeman-splitting-induced circular polarization translates to a 1 sigma upper limit on the parallel, or toroidal, component of the magnetic field of 300 mG. Assuming magnetic and thermal pressure balance in the disk, this magnetic field upper limit corresponds to a model-dependent estimate of the accretion rate through the molecular disk of 10^-1.9 alpha solar masses per year for the case where the magnetic field lies along the line of sight.

14 pages, 3 figures. To appear in ApJ, Part I

References in corpus (2)

• A Survey for H${}_2$O Megamasers in Active Galactic Nuclei -- II. A Comparison of Detected and Undetected Galaxies
• VLBA Continuum Observations of NGC 4258: Constraints on an Advection-Dominated Accretion Flow

Cited by in corpus (18)

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• Near-Infrared Polarimetric Adaptive Optics Observations of NGC 1068: A torus created by a hydromagnetic outflow wind
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• Theory and Extragalactic Masers