1. WG7.4: Modelling the Galactic Magnetic Field Paddy Leahy (for Althea Wilkinson and Tony Banday)

2. 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 interest in the modelling effort, but were not able to participate in 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

3. 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)

4. 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

5. OBSERVED COMPONENTS Synchrotron Free-free (H , RRLs, RMs, ?) –Temperature diagnostics? Dust –Thermal component –Anomalous dust-correlated component (dust or synchrotron?)

6. 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

7. CONSTRAINING the model Common data format? HEALPix - who generates these? Dedicated observation programmes?

8. 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