1. Galactic Magnetic Field Research with LOFAR Wolfgang Reich Max-Planck-Institut für Radioastronomie Bonn, Germany

2. The Galactic magnetic field What we want to know : - global field structure: disk + halo - regular/random component f(r) - field strength f(r) - field reversals - local peculiarities What to do: - measurements - modelling - what can LOFAR contribute ?

3. The Galactic magnetic field Observational methods (local results): Starlight polarization: perpendicular field  3 kpc Zeeman splitting: parallel field local e.g. masers, clouds Polarized dust: perpendicular field star forming regions

4. The Galactic magnetic field Observational methods (global results): Synchrotron emission I: perpendicular field Synchrotron emission PI: perpendicular / regular component Rotation measures (PSR, EGS): parallel field Needs: cosmic ray density/spectrum f(r,z) thermal electron density and filling factor f(r,z)

5. Total intensity all-sky surveys Longair (2004)

6. Polarized intensity all-sky surveys depolarization 1.4 GHz DRAO (Wolleben et al., 2006) + Villa Elisa (Testori et al., 2008) 22.8 GHz WMAP (Page et al. 2007) Low percentage polarization outside local features.

7. RMs from Extragalactic Sources Currently available data (compiled by JinLin Han) Brown et al. 2007 Brown et al. 2003 Han et al. 1997

8. CR thermal n e B-field Synchrotron Emission I ( ) + PI ( ) NE2001 RM,  ( ) Galactic components

9. Models should agree with all observations Radio observational constrains on Galactic 3D-emission models Sun X.H., Reich, W., Waelkens, A., Enßlin, T.A. 2008, A&A, 477, 573 + some recent progress Simulations based on the “Hammurabi” code: Waelkens, A., Jaffe, T., Reinecke, R., Kitaura, F., Enßlin T.A., 2008, A&A, submitted (astro-ph 0807.2262)

10. Galactic 3D models Various 3D models available for: thermal electron distribution -- PSR DMs (NE2001) magnetic field structure -- RMs of pulsars / EGSs CR electrons -- propagation of CR New 3D model in agreement with all-sky observations: optically thin free-free emission from WMAP low-frequency thermal absorption 22, 45, 408, 1420 MHz I maps 22.8 GHz PI map (= intrinsic) highly depolarized 1.4 GHz PI map RMs of EGS (PSR RMs not yet included)

11. The method applied

12. Galactic thermal electron distribution NE2001 (Cordes & Lazio, 2002) NE2001 does not reproduce low frequency absorption diffuse thermal emission is clumpy in the plane: HII regions + small filling factor f e (z) (Berkhuijsen et al., 2006) thermal component: WMAP NE2001 NE2001 +f e WMAP NE2001 +f e

13. RM data of EGS High latitude RMs interpolated RM map includes new Effelsberg L-band RM survey (~1500 sources : Han, Reich et al. in prep.) RMs asymmetric to the plane and the centre towards the inner Galaxy. Not local (Han et al. 1999). RMs along the Galactic plane EGS in CGPS (Brown et al. 2003 ) EGS in SGPS (Brown et al. 2007) Large RM fluctuations ! Han et al. 1997

14. radial and height dependence Galactic 3D modeling: the regular magnetic disk field ASS+RINGASS+ARMBSS local regular field: 2  G regular center field: 2  G scale height: 1 kpc ASS BSS

15. radial and height dependence: |z|<1.5 kpc |z|>1.5 kpc (not sensitive) strength at solar radius: 7  G at z = 1.5kpc Galactic 3D modeling: regular magnetic halo field RM-Observations don’t agree with BSS+Halo model CGPS RMs: Brown et al. B-disk - B-Halo B-disk + B-Halo Moss & Sokoloff, 2008, AA, 487,197: galactic dynamo theory is unable to accout for this B-field configuration

16. Disk field: ASS + one reversal

17. Galactic 3D modeling: random fields, CR electrons and local excess of synchrotron emission CR electrons: power law spectral index of –3 (high)/ -2(low) normalization factor: truncation at 1 kpc Local excess of synchrotron emission: Observational evidence isotropic high latitude (>30°) emission enhanced local CR electrons OR random fields Random fields: Gaussian, homogeneous (3  G); high-resolution sim. (Kolmogorov) Fleishman & Tokarev (1995)

18. Galactic 3D modeling: fit of 22.8 GHz (PI) observations ASS field consistent with PI asymmetry in the plane PI N-S asymmetrie too large

19. Galactic 3D modeling: depolarization at 1.4 GHz fan region Loop I NPS problem: modeled depolarization insufficient !! proposed solution f nb = f e f c f e : filling factor of ne f c : coupling factor between ne and b let b ~ n 0.5, f c ~f e 0.5, f nb =f e 1.5 for f e =0.05, f nb = 0.01 RM=RM 0 +RM r /f nb 0.5 original f nb =0.01 Large RM scatter

20. CGPS RM-data (Brown et al., 2001) overlaid on the Effelsberg 11cm total intensity survey (Fürst et al., 1990) W1 Mean RM ~ -150 rad m -2 lb=119°,2.5°: map size 8°x5° Large RM Scatter

21. Implications in turn for NE2001: NE2001 needs modification by including filling factor and scale height of thermal electrons  Sun et al. (2008) suggest: Scale height increase from ~1 kpc to ~2 kpc Halo-field will decrease to 2  G avoids unphysical truncation of CR at z = 1 kpc Gaensler et al., 2008, astro/ph 0808.2550 – reanalysis of scale height gives ~1.8 kpc !!

22. All-sky simulations at 15‘ angular resolution: diffuse Galactic emission to be seen by LOFAR synchrotron spectral index  = 2.5 Galactic plane: 0° < L < 90°, -20° < B < 20° 10 MHz 50 MHz 30 MHz 70 MHz

23. Expected LOFAR input for 3D-modelling synchrotron spectral index variations thermal scale height local synchrotron emissivity in 3D by optically thick HII-regions N e – B relation for small clumps high resolution Faraday screen mapping with high RM resolution

24. Problem: Cloud Distance ?  RM - Synthesis ABC FS +5 B A C LOFAR will detect small RMs from small clouds OFF ON

25. High resolution 151 MHz simulations (Sun & Reich) I 160..100K Same area with different distribution of random B-field I 160..100K Random B-field spectrum with Kolmogorov-like power law PI 20..0K RM +/-70 rad/m 2 mean -8 +/-30 PC 4.6+/- 2.3% Field size 6°x6° resolution 7.2” centre (l,b) 190°, 48°

26. Thank you !