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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

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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


A survey of the global magnetic fields of giant molecular clouds

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)


A survey of the global magnetic fields of giant molecular clouds

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)


A survey of the global magnetic fields of giant molecular clouds

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%


A survey of the global magnetic fields of giant molecular clouds

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


A survey of the global magnetic fields of giant molecular clouds

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)


A survey of the global magnetic fields of giant molecular clouds

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…”


A survey of the global magnetic fields of giant molecular clouds

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…”


A survey of the global magnetic fields of giant molecular clouds

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.


A survey of the global magnetic fields of giant molecular clouds

observing magnetic fields in molecular clouds

-- polarized dust emission:submm telescopes; Mauna Keamm-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


A survey of the global magnetic fields of giant molecular clouds

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


A survey of the global magnetic fields of giant molecular clouds

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)


A survey of the global magnetic fields of giant molecular clouds

simulated GMC

βt = M2β = 50

weak field

(also didβt = 5)

Ostriker, Stone, & Gammie (2001)


A survey of the global magnetic fields of giant molecular clouds

Dotson et al. (in prep.)

Dotson et al. (in prep.)


A survey of the global magnetic fields of giant molecular clouds

OP = 0.73

OP = 0.97 OP = 0.06


A survey of the global magnetic fields of giant molecular clouds

OP = 0.80

OP = 0.98 OP = 0.14


A survey of the global magnetic fields of giant molecular clouds

BGMC from SPARO

NGC 6334 region

NGC 6334

cloud

bias- corrected

NGC 6334

region


A survey of the global magnetic fields of giant molecular clouds

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


A survey of the global magnetic fields of giant molecular clouds

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


A survey of the global magnetic fields of giant molecular clouds

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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