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) -- 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) ( Brunt & Heyer 2002 )

Ostriker, Stone, & Gammie (2001) 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) 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)

data from SPARO 2003 winter-over ( Li et al 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%

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

dispersion in field direction vs. energy density of uniform field   ° 20° 10°  30° 5°5°

dispersion in field direction vs. energy density of uniform field   ° 20° 10°  30° 5°5° mod. C.F.

dispersion in field direction vs. energy density of uniform field   ° 20° 10°  30° 5°5° mod. C.F.

dispersion in field direction vs. energy density of uniform field   ° 20° 10°  30° 5°5° mod. C.F. Problems: 1 - inclination of B unif 2 - beam dilution

dispersion in field direction vs. energy density of uniform field   ° 20° 10°  30° 5°5° mod. C.F. Problems: 1 - inclination of B unif 2 - beam dilution

dispersion in field direction vs. energy density of uniform field   ° 20° 10°  30° 5°5° mod. C.F. Problems: 1 - inclination of B unif 2 - beam dilution

dispersion in field direction vs. energy density of uniform field   ° 20° 10°  30° 5°5° mod. C.F. Problems: 1 - inclination of B unif 2 - beam dilution

dispersion in field direction vs. energy density of uniform field   ° 20° 10°  30° 5°5° mod. C.F. Problems: 1 - inclination of B unif 2 - beam dilution

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

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

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

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

Conclusions from SPARO GMC survey i. i. For typical GMCs, the internal dispersion   in magnetic field direction is estimated to be ~ 28° ii. ii. 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. iii. iii. 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.

observing magnetic fields in molecular clouds ( Bourke et al ) -- 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 B l.o.s.

SPARO B-vectors on IRAS 100  m maps (equatorial coordinates) NGC 6334 d ~ 1.7 kpcCarina d ~ 2.7 kpc G d ~ 3.0 kpc G d ~ 5.3 kpc

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

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

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

Ostriker, Stone, & Gammie (2001) simulated GMC β t = M 2 β = 50 weak field (also did β t = 5)

Dotson et al. (in prep.)

OP = 0.73 OP = 0.97 OP = 0.06 OP = 0.97 OP = 0.06

OP = 0.80 OP = 0.98 OP = 0.14

NGC 6334 region bias- corrected B GMC from SPARO NGC 6334 cloud NGC 6334 region

-- observers looking through “holes” in diffuse ISM gas -- we’ll consider NGC 6334 (d = 1.7 kpc), but not others Selective extinction vs. distance for Heiles (2000) stars 1 kpc 3 kpc 2 kpc 0.7 mag E ( B-V )

-- cell size:  l x  b x  d = (300 x 120 x 500) pc -- foreground correction: Marraco et al only 22 of 75 cells have at least five correctable background stars -- only 11 cells have sufficient order Analysis of optical polarimetry data NGC 6334 Drimmel & Spergel 2001

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

-- reject cells with order parameter (O.P.) < reject cells with fewer than five residues

Polarization residues for 3 of our 75 cells -- reject cells with order parameter (O.P.) < 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

Rosolowsky et al. 2003; M33 Rotation axis parallel to Galactic plane simulations observation Rotation axis perp. to Galactic plane

Rosolowsky et al Turbulent Beta simulations observation