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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

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 )

-- 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)


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)

Ostriker, Stone, & Gammie (2001)


Data from sparo 2003 winter over li et al 2006 ap j
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%


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


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


Dispersion in field direction vs energy density of uniform field
dispersion in field direction vs. energy density of uniform field

50°

30°

sq

20°

10°

1

10

100

b-1


Dispersion in field direction vs energy density of uniform field1
dispersion in field direction vs. energy density of uniform field

50°

30°

sq

20°

mod. C.F.

10°

1

10

100

b-1


Dispersion in field direction vs energy density of uniform field2
dispersion in field direction vs. energy density of uniform field

50°

30°

sq

20°

mod. C.F.

10°

1

10

100

b-1


Dispersion in field direction vs energy density of uniform field3
dispersion in field direction vs. energy density of uniform field

50°

30°

sq

20°

mod. C.F.

10°

Problems:

1 - inclination of Bunif

2 - beam dilution

1

10

100

b-1


Dispersion in field direction vs energy density of uniform field4
dispersion in field direction vs. energy density of uniform field

50°

30°

sq

20°

mod. C.F.

10°

Problems:

1 - inclination of Bunif

2 - beam dilution

1

10

100

b-1


Dispersion in field direction vs energy density of uniform field5
dispersion in field direction vs. energy density of uniform field

50°

30°

sq

20°

mod. C.F.

10°

Problems:

1 - inclination of Bunif

2 - beam dilution

1

10

100

b-1


Dispersion in field direction vs energy density of uniform field6
dispersion in field direction vs. energy density of uniform field

50°

30°

sq

20°

mod. C.F.

10°

Problems:

1 - inclination of Bunif

2 - beam dilution

1

10

100

b-1


Dispersion in field direction vs energy density of uniform field7
dispersion in field direction vs. energy density of uniform field

50°

30°

sq

20°

mod. C.F.

10°

Problems:

1 - inclination of Bunif

2 - beam dilution

1

10

100

b-1


Conclusions from comparison with models
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)


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…”


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…”


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…”


Conclusions from sparo gmc survey
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.


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 )


Sparo b vectors on iras 100 m m maps equatorial coordinates
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


SPARO B-vectors on PAH maps (equat. coords)

MSX

Band A

(7-11 μm)

-- Carina: B parallel to edges of bubbles: flux-freezing


Kuiper et al 1987 survey of 65 prominent gmcs in southern sky
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)

-- PAHs trace boundaries of HII bubbles

MSX Band A (7-11 μm)

Smith et al. (2000)


simulated GMC

βt = M2β = 50

weak field

(also didβt = 5)

Ostriker, Stone, & Gammie (2001)


Dotson et al. (in prep.)

Dotson et al. (in prep.)


OP = 0.73

OP = 0.97 OP = 0.06


OP = 0.80

OP = 0.98 OP = 0.14


BGMC from SPARO

NGC 6334 region

NGC 6334

cloud

bias- corrected

NGC 6334

region



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


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


Rosolowsky et al 2003 m33
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


Rosolowsky et al 2003
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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