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A Survey of the Global Magnetic Fields of Giant Molecular Clouds

A Survey of the Global Magnetic Fields of Giant Molecular Clouds. Giles Novak, Northwestern University. Instrument: SPARO Collaborators: P. Calisse, D. Chuss, M. Krejny, H. Li. CO J=1-0 emission from GMCs in the Perseus arm (~ 2 kpc). ( Brunt & Heyer 2002 ).

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A Survey of the Global Magnetic Fields of Giant Molecular Clouds

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  1. A Survey of the Global Magnetic Fields of Giant Molecular Clouds Giles Novak, Northwestern University Instrument: SPARO Collaborators: P. Calisse, D. Chuss, M. Krejny, H. Li

  2. CO J=1-0 emission from GMCs in the Perseus arm (~ 2 kpc) ( Brunt & Heyer 2002 ) -- low overall star formation efficiency: -- mechanical support by magnetic fields? (e.g., Shu et al. ‘87; Mouschovias & Ciolek ‘99; Basu & Ciolek ‘04) -- are GMCs dynamic structures? (e.g., Hartmann et al. `01; Elmegreen & Scalo `04; Mac Low & Klessen `04)

  3. simulated GMC 3-d MHD code; compressible; has self-gravity; Isothermal this map assumes strong B-field can reproduce size/line-width relationship that is observed in real GMCs Ostriker, Stone, & Gammie (2001)

  4. simulated GMC 3-d MHD code; compressible; has self-gravity; Isothermal this map assumes strong B-field can reproduce size/line-width relationship that is observed in real GMCs dynamical collapse: role of B-field; transport of angular momentum: (Allen, Li & Shu ’03) turbulence can affect ang. mom. transport: (Ballesteros-Paredes et al. ’06) IMF: from turbulent fragmentation (Padoan & Nordlund ’02) magnetic levitation? (Shu et al. ’04) Ostriker, Stone, & Gammie (2001)

  5. data from SPARO 2003 winter-over( Li et al. 2006 Ap.J. ) • we observed four GMCs in the Galactic disk • each map covers hundreds of sq. arcmin • total number of polarization detections: 130 • median degree of polarization: P = 2.0%

  6. NGC 6334 Carina Nebula G 333.6 G 331.5 histograms of B-field direction for each GMC -- next: we focus on internal structure of field -- Carina is different; very advanced stage of star formation -- G331.5 lies at 5.3 kpc

  7. NGC 6334 Carina Nebula G 333.6 G 331.5 histograms of B-field direction for each GMC sq = 22.3° sq = 21.6° -- next: we focus on internal structure of field -- Carina is different; very advanced stage of star formation -- G331.5 lies at 5.3 kpc

  8. dispersion in field direction vs. energy density of uniform field 50° 30° sq 20° 10° 5° 1 10 100 b-1

  9. dispersion in field direction vs. energy density of uniform field 50° 30° sq 20° mod. C.F. 10° 5° 1 10 100 b-1

  10. dispersion in field direction vs. energy density of uniform field 50° 30° sq 20° mod. C.F. 10° 5° 1 10 100 b-1

  11. dispersion in field direction vs. energy density of uniform field 50° 30° sq 20° mod. C.F. 10° 5° Problems: 1 - inclination of Bunif 2 - beam dilution 1 10 100 b-1

  12. dispersion in field direction vs. energy density of uniform field 50° 30° sq 20° mod. C.F. 10° 5° Problems: 1 - inclination of Bunif 2 - beam dilution 1 10 100 b-1

  13. dispersion in field direction vs. energy density of uniform field 50° 30° sq 20° mod. C.F. 10° 5° Problems: 1 - inclination of Bunif 2 - beam dilution 1 10 100 b-1

  14. dispersion in field direction vs. energy density of uniform field 50° 30° sq 20° mod. C.F. 10° 5° Problems: 1 - inclination of Bunif 2 - beam dilution 1 10 100 b-1

  15. dispersion in field direction vs. energy density of uniform field 50° 30° sq 20° mod. C.F. 10° 5° Problems: 1 - inclination of Bunif 2 - beam dilution 1 10 100 b-1

  16. conclusions from comparison with models : totalmagnetic energy density kinetic energy density -- consistent with Crutcher et al. (1999) -- not consistent with Padoan et al. (2001), Padoan & Nordlund (2002)

  17. Is there continuity between GMC fields and larger-scale Galactic fields? Searches for correlation of BGMC with orientation of Gal. plane: Glenn et al. ‘99 … “…appear randomly oriented wrt plane…” Hildebrand ‘02 … “…apparently random orientation…”

  18. BGMC from SPARO ( Li et al. `06 ApJ ) Is there continuity between GMC fields and larger-scale Galactic fields? Searches for correlation of BGMC with orientation of Gal. plane: Glenn et al. ‘99 … “…appear randomly oriented wrt plane…” Hildebrand ‘02 … “…apparently random orientation…”

  19. BGMC from SPARO ( Li et al. `06 ApJ ) NGC 6334 cloud Is there continuity between GMC fields and larger-scale Galactic fields? Searches for correlation of BGMC with orientation of Gal. plane: Glenn et al. ‘99 … “…appear randomly oriented wrt plane…” Hildebrand ‘02 … “…apparently random orientation…”

  20. Conclusions from SPARO GMC survey • For typical GMCs, the internal dispersion sq in magnetic field direction is estimated to be ~ 28° • By comparing this with the model of Ostriker et al. (2001) we infer that the total magnetic energy density is comparable to the kinetic energy density of turbulence. • By considering the distribution of GMC mean field directions, and by comparing with optical polarimetry, we find evidence for continuity between GMC fields and Galactic fields.

  21. observing magnetic fields in molecular clouds -- polarized dust emission: submm telescopes; Mauna Kea mm-wave interferometers Kuiper Airborne Obs. (early days) -- Zeeman splitting observ.: - radio freq. molecular lines (typ. OH absorption) - gives Bl.o.s. ( Bourke et al. 2001 )

  22. SPARO B-vectors on IRAS 100 mm maps(equatorial coordinates) NGC 6334 d ~ 1.7 kpc Carina d ~ 2.7 kpc G 333.6 d ~ 3.0 kpc G 331.5 d ~ 5.3 kpc

  23. SPARO B-vectors on PAH maps (equat. coords) MSX Band A (7-11 μm) -- Carina: B parallel to edges of bubbles: flux-freezing

  24. Kuiper et al. (1987) survey of 65 prominent GMCs in southern sky -- analysis by Kuiper et al. is based on IRAS maps Carina Nebula

  25. Polycyclic Aromatic Hydrocarbons (PAHs) in Carina Nebula (Galactic coords) -- PAHs trace boundaries of HII bubbles MSX Band A (7-11 μm) Smith et al. (2000)

  26. simulated GMC βt = M2β = 50 weak field (also didβt = 5) Ostriker, Stone, & Gammie (2001)

  27. Dotson et al. (in prep.) Dotson et al. (in prep.)

  28. OP = 0.73 OP = 0.97 OP = 0.06

  29. OP = 0.80 OP = 0.98 OP = 0.14

  30. BGMC from SPARO NGC 6334 region NGC 6334 cloud bias- corrected NGC 6334 region

  31. Foreground correction gives polarization residue(Marraco et al. 1993)

  32. Foreground correction gives polarization residue(Marraco et al. 1993) -- reject cells with order parameter (O.P.) < 0.3 -- reject cells with fewer than five residues

  33. Polarization residues for 3 of our 75 cells -- reject cells with order parameter (O.P.) < 0.3 -- reject cells with fewer than five stars -- save the (equal-weight Stokes’) mean B-field angle for each surviving cell O.P.= 0.41 O.P.= 0.28 O.P.= 0.21

  34. Rosolowsky et al. 2003; M33 1 0.8 observation 0.6 0.4 0.2 simulations Rotation axis perp. to Galactic plane Rotation axis parallel to Galactic plane

  35. Rosolowsky et al. 2003 1 0.8 observation 0.6 0.4 0.2 simulations 0 0.1 1 10 100 Turbulent Beta

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