WG7.4: Modelling the Galactic Magnetic Field

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WG7.4 Modelling the Galactic Magnetic Field

• Paddy Leahy
• (for Althea Wilkinson and Tony Banday)

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Members

• Initial Telecon
• Tony Banday
• Althea Wilkinson
• Carlo Burigana
• Rod Davies
• Richard Davis
• Martin Giard
• Giovanna Giardino
• Paddy Leahy
• Roberta Paladini
• Luca Valenziano
• Andre Waelkens
• Steven Gibson

• In addition, the following people expressed
  interestin the modelling effort, but were not
  able to participatein the telecon
• Clive Dickinson
• Pablo Fosalba
• Torsten Ensslin
• Laura LaPorta
• Juan Macias-Perez
• Michele Maris
• Wolfgang Reich
• Jan Tauber
• Russ Taylor
• Richard Wielebinski
• Carlos del Burgo

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Aims

• Generate a model sky (or skies)
• Test software for fitting the Planck Galactic
  (polarized) emission
• Provide input training sets for (polarized)
  component separation (WG2)
• A scientific output of the mission (after the
  model is iterated against the Planck data
  itself)

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REPRESENTATION of the model

• A 3D grid in Earth centred l,b,r coordinates
• a radially nested HEALPix structure would seem
  convenient
• target physical resolution
• target angular resolution l,b grid matched to
  Planck resolution, but with sufficient fine-scale
  granularity to capture relevant physical
  processes
• variation of radial grid size with radius
• 2D emission by appropriate radial integration
• Already implemented by Waelkens Ensslin
• See poster

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OBSERVED COMPONENTS

• Synchrotron
• Free-free (H?, RRLs, RMs, ?)
• Temperature diagnostics?
• Dust
• Thermal component
• Anomalous dust-correlated component
• (dust or synchrotron?)

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PARAMETERISATION

• spiral structure model of the Milky Way for
  various components
• does not yet exist, even the number and
  distribution of the spiral arms may be uncertain
  (eg. 4 arm structure from HI may be contradicted
  by 2-arm structure in the infrared)
• dynamic properties rotation curve, streaming
  motions
• scale lengths and heights of various stellar
  populations and ISM   components in the disk
• explicit model for the Galactic halo
• specific nearby structures
• magnetic field
• large-scale ordering of the field parallel to the
  spiral arms and in the plane of the disk
• spiral structure
• small-scale structure the magnetic field shows
  real "structure", i.e. non-random phases
  variations between arm and interarm regions, and
  with gas phase e.g. between GMCs, CNM, WNM/WIM,
  HIM
• CR spectrum
• dust emission spectra as functions of composition

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CONSTRAINING the model

• Common data format? HEALPix - who generates
  these?
• Dedicated observation programmes?

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OPEN QUESTIONS to resolve

• Can we define some simple starting points?
• Are existing parameterizations of the components
  consistent?
• How do we define "sub-groups" and sub-group
  leaders overlap with other WG7 groups?
• Aims before WG7 meeting in September