Thanks for cooperation with Dick Manchester (ATNF, Australia),

1. Magnetic fields in our GalaxyJinLin HanNational Astronomical ObservatoriesChinese Academy of SciencesBeijing, Chinahjl@bao.ac.cn Thanks for cooperation with Dick Manchester (ATNF, Australia), G.J. Qiao (PKU, China), A.G. Lyne (Jodrell Bank, UK), (K. Ferriere: Obs. Midi-Pyr. France)

2. Magnetic fields in our GalaxyWhat RMs of pulsars & EGRes can tell us? • Some background, reminding • Knowledge 10 years ago • Current knowledge • Central field & halo field • disk field • directions • strength • spatial magnetic energy spectrum We advanced a lot of knowledge on magnetic fields of our Galaxy in last 10 years! --- More coming.

3. Observational tracers of magnetic fields • Polarization of starlight:perpendicular field in 2 or 3 kpc orientation // B⊥ ------------- 9000 stars • Zeeman splitting: parallel field, in situ (masers, clouds) △ ∝ B// ------ 30 masers • Polarization at infrared, mm:perpendicular field orientation // B⊥ ------------- star formation regions • Synchrotron radiation:vertical field structures (added) total intensity S ∝ B⊥2/7, p%∝ B⊥u2 / B⊥t2 • Faraday rotation:parallel field, integrated (the halo & disk) RM∝∫ne B//ds ------ 550 pulsars + >2000 EGSes

4. Starlight polarization:local field // arm • 9000 stars have polarization measured • mostly nearby (1~2kpc) • polarization percentage increases with distance Zweibel & Heiles 1997, Nature 385,131 Berdyugin & Teerikorpi 2001, A&A 368,635

5. Zeeman Effect: B in molecular clouds >30 people working for >30 years, get <30 good measurements! Difficult &Bad Luck! Bourke et al. 2001, ApJ 554, 916

6. Maser B-fields:Nothing to do with large-scale B-field?! Reid & Silverstein 1990, ApJ 361, 483 Fish et al. 2003 41 clockwise 33 counterclockwise Assume Bφ>> Br or Bz ne: ISM: 1cm-3 ==> GMC: 103cm-3 ==> OH-maser: 107cm-3

7. Observational tracers of magnetic fields • Polarization of starlight: perpendicular field in 2 or 3 kpc orientation // B⊥ ------------- 9000 stars • Zeeman splitting: parallel field, in situ (masers, clouds) △ ∝ B// ------ 30 masers • Polarization at infrared, mm : perpendicular field orientation // B⊥ ------------- star formation regions • Synchrotron radiation : vertical field structures (added) total intensity S ∝ B⊥2/7, p% ∝ B⊥u2 / B⊥t2 • Faraday rotation:parallel field, integrated (the halo & disk) RM∝∫ne B//ds ------ 500 pulsars + >1000 EGSes Magnetic field around GC Comparison of magnetic fields of nearby Galaxies to our owns

8. thermal emission (of dusts) aligned by B-field in the clouds Polarization at mm, sub-mm, infraredWorking toward measure B-field of galactic scale Hildebrand et al. PASP 112, 1215

9. Poloidal & Toroidal fields near GC (after Novak et al. 2003) Predicted B-direction GC Large-scale Toroidal fields permeated in the central molecular zone (170pc*30pc) sub-mm obs of p% toroidal field directions determined by averaged RMs of plumes or SNR! Poloidal field filaments Unique to GC ---dipolar geometry!? (Yusef-Zadeh et al., 1984;1997 Morris 1994; Lang et al.1999) 150pc

10. Magnetic fields in our Galaxy: near GC Spiral arms to centre: continue near GC? Yes in NGC 2997 (Han et al. 1999) - How strong? Do not know! Poloidal fields: reason for jets? dipole field? related to vertical-B? how strong? (from B.D.C. Chandran 2000)

11. Synchrotron radiation:transverse B-structuresGlobal B-field structure from linearly polarized emission • Two Possible origin of polarization: • Large-scale magnetic field as vectors shown (convention) • Anisotropic random field compressed by large-scale density wave RM maps helps on directions of (disk &) halo field! MPIFR has a group working on this for 25 years! No information of B-directions! Han et al. 1999, A&A 384, 405

12. Observational tracers of magnetic fields • Polarization of starlight: perpendicular field in 2 or 3 kpc orientation // B⊥ ------------- 9000 stars • Zeeman splitting: parallel field, in situ (masers, clouds) △ ∝ B// ------ 30 masers • Polarization at infrared, mm : perpendicular field orientation // B⊥ ------------- star formation regions • Synchrotron radiation : vertical field structures (added) total intensity S ∝ B⊥2/7, p% ∝ B⊥u2 / B⊥t2 • Faraday rotation:parallel field, integrated (the halo & disk) RM∝∫ne B//ds ------ 550 pulsars + >2000 EGSes

13. Pulsars: Uique probes for Large-scale Galactic B-field Pulsar distribution • Widely distributed in Galaxy • Distance from DM: 3-D B-field • Linearly polarized: RM easy to obs • No intrinsic RMs: Direct <B>

14. Why? Pulsars as probes for Galactic B-field • Polarized.Widely spread in our Galaxy. Faraday rotation: • Distances estimated from pulse dispersion: • <===the delay tells DM • the rotation of position • angles tells RM value===> • Average field strength is

15. Knowledgeof 10 years ago ……

16. Galactic magnetic fields: 10 years ago disk field:* 3 models* which one? • Halo field:*no idea on halo field * Poloidal fieldsnear GC:Yessee nonthermal filaments Concentric Rings Axi-symmetric Bi-Symmetric Spiral Rings model spiral (ASS) (BSS)

17. Axi-Symmetric Spiral modelby J.P. Vallee • Main Problem: fields go across the arms • Just one radius range for reversed fields • Not consistent with field reversals near -- Perseus arm?? -- the Norma arm !! ? ? BSS reversal BSS reversal

18. by R. Rand & S. Kulkarni (1989)R. Rand & A.Lyne(1994) Ring model:Concentric rings of reversed fields • Selection effect problem ?? • Field lines go across the arms? • Inconsistent Formula for the BSS when modeling ?? It is the zero-order modelling only for azimuthal magnetic field ! There were not as many pulsar RMs as today….

19. Bi-Symmetric Spiral Model Proposed from RMs of Extragalactic Radio Sources: Simard-Normandin & Kronberg (1980) Sofue & Fujimoto (1983) Confirmed byPulsar RMs: Han & Qiao (1994) Indrani & Deshpande (1998) Han, Manchester, Qiao (1999) Han,Manchester, Lyne, Qiao(2002) Supported bystarlight polarization Heiles (1996) The best match to all evidence field reversals & pitch angle – 8°±2° ( the field stronger in interarm region ? ? )

20. Galactic B-Field：10 years ago 30kpc Halo field：no idea！ Center: Poloidal field Sun Galactic center Disk field: A few kpc! 3 models: which？

21. Current knowledge …… • Central field & halo field • disk field: directions & Strength • magnetic energy spectrum

22. Poloidal & Toroidal fields near GC (from Novak et al. 2003) Predicted B-direction GC Toroidal fields (Novak et al. 2003, 2000) permeated in the central molecular zone (400pc*50pc) sub-mm obs of p% toroidal field directions determined by averaged RMs of plumes or SNR! Poloidal field filaments Unique to GC --- dipolar geometry! (Morris 1994; Lang et al.1999) 150pc

23. Magnetic fields in our Galaxy: near GC Spiral arms & B- fields continue near GC? Yes in NGC 2997 (Han et al. 1999) - How strong? Poloidal fields reason for jets? dipole field? related to vertical-B? how strong? (from B.D.C. Chandran 2000)

24. To study halo field:unique to our Galaxy RM distribution Pulsars • The largest edge-on Galaxy in the sky • Pulsars and extragalactic radio sources as probes

25. To study halo field:unique to our Galaxy Extragalactic Radio Sources RM distribution <B> away from us RM<0 RM>0 <B> to us • The largest edge-on Galaxy in the sky • Pulsars and extragalactic radio sources as probes

26. Anti-symmetric RM sky: A0 dynamo(Han et al. 1997 A&A322, 98) Evidence for global scale • High anti-symmetry to the Galactic coordinates • Only in inner Galaxy • nearby pulsars show it at higher latitudes Implications • Consistent with field configuration of A0 dynamo • The first dynamo mode identified on galactic scales Bv

27. Unpublished database ……EGRes

28. Magnetic field configurations for basic dynamos A0 M31:only 21 polarized bright background sources available !! Han, Beck, Berkhuijsen (1998): An even mode (S0) dynamo may operate in M31 ! S0 S1

29. RMs of EGRs for the halo B-field Only about 1000 RMs available in literature upto now... We are using Effelsberg -100m telescope to make a RM survey of 1700 sources, enlarge the cover density by a factor of three in most sky area……

30. Current knowledge …… • Central field & halo field • disk field: • directions • Strength • magnetic energy spectrum

31. Pulsar RM distribution in Galactic planeRed: new measurements by Parkes 64m telescope (Han et al. 2005, to be submitted)

32. Pulsar RM distribution in Galactic planered: new measurements by Parkes 64m telescope

33. CCW B-field along the Norma arm: from New Pulsar RMs possible field directions Field directionsnewly determined ?? Coherent B-fielddirections>5 kpc along Norma arm Another reversed field in large-scale? Han et al. 2002, ApJ 570, L17

34. Pulsar RM distribution in Galactic planered: new measurements by Parkes 64m telescope (Han et al. 2005, to be submitted)

35. Large-scale magnetic field in the Galactic disk(Han et al. 2005, to be submitted)

36. Large-scale magnetic field in the Galactic disk(Han et al. 2005, to be submitted) Weisberg et al. 2004: large-scale magnetic fields lies in arm region?! Yes! • always counterclockwise in arm region! • clockwise in interarm region ? • Different from previous models ! Tight BSS？ • More data still needed!

37. Current knowledge …… • Central field & halo field • disk field: • directions • Strength • magnetic energy spectrum

38. Radial dependence of regular field strength(Han et al. 2005, to be submitted)

39. Radial dependence of regular field strength(Han et al. 2005, to be submitted)

40. Current knowledge …… • Central field & halo field • disk field: directions & Strength • magnetic energy spectrum

41. Why our Galaxy has magnetic field?Probably Dynamo!How dynamo works? Alpha-Omega effect. Dynamo Really works? Computer Simulations….

42. Many Simulations of dynamos ---- check spacial B-energy spectrum & its evolution e.g. Magnetic energy distribution on different spatial scales (k=1/λ) • No real measurements • to check whether • dynamo works or not! • Many papers by • N.E. L. Haugen, A. Brandenburg, W. Dobler, ….. • A. Schekochihin, S.C. Cowley, S. Taylor, J. Moron, ….. • E. Blackman, J. Maron ….. • Others ….. Far away from telling anything about a real galaxy …… Don’t know much about the large-scale magnetic field ...

43. What spatial magnetic energy spectrum does our Galaxy have?

44. Kolmogorov over 12 orders in scale? Spatial fluctuation spectrum for electron density “The Big Powerlaw in the Sky” (Armstrong, Rickett & Spangler 1995) 10 pc B-field & electrons coupling? If so, B-energy spectrum? 1000 km

45. Minter & Spangler 1996 Spatial energy spectrum of BPreviously only available information from RM structure function λ< ~4pc: consistent to Kolmogorov 3D 80>λ> ~4pc: turbulence in 2D?

46. Pulsar RM distribution in Galactic planered: new measurements by Parkes 64m telescope

47. Spatial magnetic energy spectrum of our Galaxy(Han et al. 2004, ApJ 610, 820) By pulsar RM/DM Email from A. Minter Minter & Spangler 1996

48. We now can tell about ---- Global structure of Galactic magnetic field • Halo field structure • Disk field structure

49. Galactic B-Field：10 years ago 30kpc Halo field：no idea！ Center: Poloidal field Sun Galactic center Disk field: A few kpc! 3 models: which？

50. Conclusive Remarks: More data needed--Pulsars are unique powerful probes • Spatial Energy spectrum • Radial dependence • Halo field • Disk field