PROPERTIES OF THE MAGNETO-IONIC MEDIUM IN THE HALO OF M51 REVEALED BY WIDE-BAND POLARIMETRY

Journal Article · Fri Feb 20 04:00:00 EST 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/800/2/92· OSTI ID:22522095

Mao, S. A.; Ott, J. ^[1]; Zweibel, E. ^[2]; Fletcher, A. ^[3]

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1. National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States)
2. Department of Astronomy, The University of Wisconsin, Madison, WI 53706 (United States)
3. School of Mathematics and Statistics, University of Newcastle, Newcastle upon Tyne, NE1 7RU (United Kingdom)

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 ∼–9 rad m{sup –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.

• OSTI ID: 22522095
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 800; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
DEPOLARIZATION
FARADAY EFFECT
FLUCTUATIONS
GALAXIES
GHZ RANGE
MAGNETIC FIELDS
POLARIMETRY
POLARIZATION
ROTATION
SCALE HEIGHT
SPATIAL DISTRIBUTION
STRUCTURE FUNCTIONS
TURBULENCE