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Properties of the Magneto-Ionic Medium in the Halo of M51 Revealed by Wide-Band Polarimetry

Lookup NU author(s): Dr Andrew Fletcher

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Abstract

We present a study of the magneto-ionic medium in the Whirlpool galaxy (M51) using new wide-band multi-configuration polarization data at L band (1-2 GHz) obtained at the Karl G. Jansky Very Large Array. By fitting the observed diffuse complex polarization Q+iU as a function of wavelength directly to various depolarization models, we find that polarized emission from M51 at 1-2 GHz originates from the top of the synchrotron disk and then experiences Faraday rotation in the near-side thermal halo of the galaxy. Thus, the scale height of the thermal gas must exceed that of the synchrotron emitting gas at L band. The observed Faraday depth distribution at L band is consistent with a halo field that is comprised of a plane-parallel bisymmetric component and a vertical component that produces a Faraday rotation of similar to-9 radm(-2). The derived rotation measure (RM) structure functions indicate a characteristic scale of RM fluctuations of less than 560 pc in the disk and approximately 1 kpc in the halo. The outer scale of turbulence of 1 kpc found in the halo of M51 is consistent with superbubbles and the Parker instability being the main energy injection mechanisms in galactic halos.

Publication metadata

Author(s): Mao SA, Zweibel E, Fletcher A, Ott J, Tabatabaei F

Publication type: Article

Publication status: Published

Journal: Astrophysical Journal

Year: 2015

Volume: 800

Issue: 2

Pages: 1-19

Online publication date: 17/02/2015

Acceptance date: 07/12/2014

ISSN (print): 0004-637X

ISSN (electronic): 1538-4357

Publisher: Institute of Physics Publishing, Inc.

URL: http://dx.doi.org/10.1088/0004-637X/800/2/92

DOI: 10.1088/0004-637X/800/2/92

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