Cosmic magnetism (KSP of the SKA)?

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Cosmic magnetism (KSP of the SKA)? understand
the origin and evolution of magnetism in the
Galaxy, extragalactic objects, clusters and
inter-galactic/-cluster space. SKADS in the MPI
für Radioastronmie (Bonn)? the Galaxy and nearby
spiral galaxies

• M 51 VLAEff 6cm
• (Fletcher Beck)?

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Galactic foreground simulationX.H. Sun, W.
Reich (MPIfR Bonn),A. Waelkens, T. Enßlin (MPE
Garching) submitted to AA

• Aim is to develop a Galactic 3D-model which
  will produce all-sky maps in total intensity,
  linear polarization and rotation measure
• Observations used to constrain the model
• All-sky intensity maps (408 MHz 1400 MHz 22.8
  GHz - WMAP)?
• All-sky polarization maps (1.4 GHz 22.8 GHz)?
• Rotation measures of extragalactic sources (1800
  NVSS sources Han et al. in prep.)

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Disk fields ASS (Axisymmetric Spiral)
reversals in arms
Fit of RMs in the plane
Fits of 408MHz I
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T.G.Arshakian, R.Beck and M.Krause (MPIfR, Bonn)
R.Stepanov and P.Frick (ICMM, Perm) submitted to
AA
Testing the magnetic field models of spiral
galaxies with the SKA SKADS science simulations

• The aim is to estimate the required number
  density of polarized sources to be
• detected with the SKA for reliable recognition
  or reconstruction of the magnetic
• field structure in nearby spiral galaxies.
• Steps
• To simulate the RM maps of a typical spiral
  galaxy for
• - the regular and turbulent magnetic field
  models (disk and halo)?
• - the thermal electron density model
• 2. To recognize or reconstruct the magnetic field
  structure from the simulated RM map
• and assess their reliability.

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Recognition of regular magnetic field structures
for ASS, BSS, QSS,
Simple magnetic field structures can be reliably
recognized from a limited RM measurements (lt50).
Recognition method provides a reliable estimate
of the pitch angle (10) and field amplitude
(10).
Simulations of a minimum number density of
polarized sources (N) for different -
inclination of a galaxy - turbulence of RM
- slope of integral number counts of polarized
sources.
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Perspectives for the SKA at 1.4 GHz

• Reconstruction of magnetic field structures is
  possible from a sample of ? 1000 RM sources
  galaxies at 1 Mpc with T lt 1 h, and 60 galaxies
  between 1 to 10 Mpc with tens to hundred hours
  with the SKA.
• Recognition can be reliably performed from a
  limited sample of ? 50 RM measurements 600
  spiral galaxies (lt10 Mpc, ?p0.2 µJy) can be
  recognized within T 15 min SKA observation
  time, and 60.000 galaxies (?100 Mpc, ?p0.015
  µJy) with T 100 h.
• The pitch angles are reproduced with accuracy of
  2o for the ASS and 1o (for the QSS). The field
  amplitude about 10 for all field models.
• High modes (BSS and QSS) are easier to
  recognize.
• The slope of number counts of polarized sources
  needs to be determined at low flux levels.
• The RM errors are much smaller at low
  frequencies RM data can be used for detection
  and recognition of weak galactic and
  intergalactic magnetic fields with LOFAR, ASKAP
  and SKA-AA if background sources are still
  polarized at low frequencies (lt300 MHz) - NEEDS
  FURTHER INVESTIGATION.