The Magnetoionic Medium

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The Magneto-ionic Medium
Russ Taylor Institute for Space Imaging
Science University of Calgary
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Spectro-polarimetry of the Galaxy

• International Galactic Plane Survey
• A short excursion to the NVSS
• Future directions

• The Global Galactic Magnetic Field
• Magnetic Fields and the ISM

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The International Galactic Plane Survey
Interferometric Surveys
Atomic Hydrogen Radio Continuum
Full Stokes Polarimetry
Full Stokes Polarimetry
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GGPS Phase I 145 lt ? lt 75
1420 MHz Continuum (Ionized gas and relativistic
plasma)
HI Line VLSR -41 km/s (neutral hydrogen gas
atoms)
Canadian Galactic Plane Survey, Taylor et al. 2003
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A kpc scale section of the Perseus Arm.
Canadian Galactic Plane Survey
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Canadian Galactic Plane Survey Polarimetry
Russ Taylor Jo-Anne Brown Andrew Gray Tom
Landecker Beulent Uyaniker Rob Ried
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Southern Galactic Plane Survey Polarimetry

John Dickey Ann Green Bryan Gaensler Marijke
Haverkorn Natalya Bizunok Jo-Anne Brown
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All-Sky Rotation Measure Grid
Pulsars 529
EGS 887
circa 2000
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CGPS
1 RM per square degree
Brown and Taylor (2001)
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Average RM through the Disk versus Longitude
CGPS
SGPS
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Lines of Sight Through the Galaxy Disk
CGPS
SGPS
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Some Recent Hypotheses about the global field

• Vallee (2005) 1 reversed ring, 2 kpc wide.
• Ring directed ccw, all else cw.
• Purely azimuthal
  field.

• Han et al. (2006) Arm-Interarm regions
  oppositely
• directed.
  Spiral field with overall
• bisymmetric
  structure.

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a
ne -gt Cordes Lazio 2002
b
Assume geometry
c
Solve for field
Brown et al. 2007
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Predicted Galactic Disk RM Distribution
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Brown et al. (2007)
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CGPS
SGPS
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What is the pitch angle the field?
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The Magnetic Field and the ISM
Magnetic Reversal Bubbles?
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The Faraday Screen
Diffuse Synchrotron Emissivity
Magneto-ionic structure introduces excess
Faraday Rotation
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The Faraday Screen
Diffuse Synchrotron Emissivity
Magneto-ionic structure introduces excess
Faraday Rotation
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Phenomenology of Diffuse Polarized Emission
Combined effects of synchrotron
emissivity syncrotron polarisation ionized
gas Galactic magnetic field
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Atomic Hydrogen Mushroom Cloud
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HI Emission
Polarisation position angle
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Total Intensity (Stokes I) CGPS in the Galactic
anticentre
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Polarized Intensity DRAO ST Effelsberg DRAO
26m
An HIM bubble
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CGPS High Latitude Polarimetry ST Data Only
Stokes I
Stokes Q
Stokes U
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Depolarization Shadows in the NVSS
Number density of NVSS catalog polarized sources
Stil and Taylor (2007)
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Depolarization Shadows in the NVSS
Number density of NVSS catalog polarized sources
Stil and Taylor (2007)
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Reprocessed NVSS Data in both bands
Ratio of band total polarized flux density to
average of individual bands
Derived Rotation Measure
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NVSS Sources p gt 4 mJy, size lt 100
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Wolleben, Landecker, Reich Wielebinski (2006)
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ALFA Arecibo L-band Feed Array
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GALFA Continuum Transit Survey
- ?? 300 MHz (1225 1525 MHz) - 1s 80 µJy
per Stokes (over full band), ?Trms 0.8 mK -
8196 frequency channels - absolute photometry on
all spatial scales to 3.4 using DRAO 26-m - sky
coverage 12,734 sq degrees (32 of the sky) -
total observing time 1600 hours over years
(2008-2011)
See poster by Sukphreet Guram
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GALFACTS Consortium

• Jo-Anne Brown University of Calgary
• Mike Davis SETI institute
• Avinash Deshpande Raman Research Institute
• Tyler Foster Dominion Radio Astrophysical
  Observatory
• Bryan Gaensler Harvard University
• Tapasi Ghosh NAIC
• Steve Gibson NAIC
• Sukphreet Guram University of Calgary
• JinLin Han Beijing Astronomical Observatory
• Marijke Haverkorn Harvard University
• Carl Heiles UC Berkeley
• Tess Jaffe University of Manchester
• Gilles Joncas Université Laval
• Roland Kothes Dominion Radio Astrophysical
  Observatory
• Charles Kerton Iowa State University
• Tom Landecker Dominion Radio Astrophysical
  Observatory
• Paddy Leahy University of Manchester
• Aui Ann Mao Harvard
• Emmanuel Momjian NAIC

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Global Magneto-ionic Medium Survey
Wolleben 12
Component Surveys
Prime Goal is Faraday Tomography of the Galactic
ISM
Brentjen and de Bruyn (2005) Schnitzeller et al.
2008
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The End
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GALFACTS

• Measuring the Galactic magnetic field and its
  role in the Galaxy
• Image the diffuse polarization in the Galaxy and
  the effects of the Faraday Screen
• Study structure and processes of the
  magneto-ionic ISM.
• Molecular cloud formation and star formation.
• Energization of the disk acceleration and
  confinement of energetic particles.
• Energy and mass flow between the disk, halo, and
  the IGM.
• RM image of both diffuse emission and compact
  background radio source population down to
  polarized intensity of 500 µJy
• Structure of the Galactic magnetic field from the
  disk to the pole.
• Generation and evolution of the Galactic magnetic
  field.
• Scientific pathfinder to SKA Cosmic Magnetism Key
  Science
• Rotation Measure Grid