PROPERTIES OF THE MAGNETO-IONIC MEDIUM IN THE HALO OF M51 REVEALED BY WIDE-BAND POLARIMETRY
- National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States)
- Department of Astronomy, The University of Wisconsin, Madison, WI 53706 (United States)
- 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, Vol. 800, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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