Magnetic Fields and

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Magnetic Fields and Star Formation
Dick Crutcher University of Illinois
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Outline of Talk

• Tests of star formation theory
• Observations
• Techniques
• Exemplars observational results
• Arecibo millennium H I survey
• starless cores L1544, L183, L1498
• low-mass star formation NGC1333 IRAS4
• high-mass cores DR21OH
• active high-mass star formation S106, W3OH
• Implications of the observations
• Conclusions

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Observational Techniques

• 1. Zeeman effect
• ?
• ? line-of-sight B
• 2. Polarization of emission from paramagnetic
  grains
• ? linear polarization ? B ? morphology of Bpos
• ? indirectly (Chandrasekhar Fermi)
• 3. Goldreich-Kylafis effect linearly polarized
  lines
• ? polarization ? or ?? B ? morphology of Bpos

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Some Telescopes Used for Study of B
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Mass to Magnetic Flux ratio M/?

• Uniform disk
• Nakano Nakamura (1978)

• Observing M/?

• ? definition

• Geometry correction

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Scaling of B with ?
1. Spherical collapse (weak magnetic fields)

• flux freezing M ? ? ?
• mass conservation

2. Disk morphology (strong magnetic fields)

• flux freezing M ? ? ?
• thermal support

Spitzer (1942)
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Arecibo H I Survey (Heiles Troland)
I opacity profile
Blos 5.6 ? 1.0 ?G
V opacity profile ? dI/dv
Blos 11 ? 3.1 ?G
Errors in V opacity profile
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L1544 Starless Core
n(H2) ? 5 ? 105 cm-3, N(H2) ? 4 ? 1022, ?? ? 13?,
Bpos ? 140 ?G, ?c ? 0.8
Crutcher
et al. (2004)
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L1544 Starless Core
n(H2) ? 1 ? 104, N(H2) ? 9 ? 1021, Blos 11 µG,
?c ? 1.1
n(H2) ? 5 ? 105 cm-3, N(H2) ? 4 ? 1022, ?? ? 13?,
Bpos ? 140 ?G, ?c ? 0.8
Crutcher
et al. (2004)
Crutcher Troland (2000)
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L183 L1498 Starless Cores
L183
L1498
Crutcher et al. (2004)
Kirk Crutcher (2005)
n(H2) ? 3 ? 105, N(H2) ? 3 ? 1022, ?? ? 13?, Bpos
? 80 µG, ?c ? 0.9
?? ? 40?
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NGC1333 IRAS4
Girart et al. (1999)
Bpos gt 1 mG
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DR21(OH)
Crutcher et al. (1999)
Lai et al. (2001)
Blos 0.4, 0.7 mG
Bpos ? 0.7 mG
n(H2) ? 2 ? 106, N(H2) ? 3 ? 1023, Blos ? 0.7 mG,
?c ? 1.1
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S 106
CO 1-0, line velocity ? 1.5 km/s
Bally Scoville (1982)
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S 106
Roberts et al. (1995)
SUBARU
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S 106
Roberts et al. (1995)
Simon (1999)
SUBARU
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S 106
Ward-Thompson
Roberts et al. (1995)
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S 106
Ward-Thompson
Simon (1999)
Roberts et al. (1995)
n(H2) ? 3 ? 105, N(H2) ? 3.3 ? 1022, Blos ? 0.45
mG, ?c ? 0.2
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W3OH
CN Zeeman, Blos 1.1 mG Falgarone et al. 2005
Gusten et al. 1994
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Results for M/?
Diffuse ISM, CNM ? lt 0.25
Molecular clouds ?C ? 1
Heiles Troland (2004)
Crutcher (2004)
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Results for M/?
Molecular clouds ?C ? 1
?
Crutcher (2004)
Crutcher (2004)
Ciolek Mouschovias (1994)
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Results for B ? ??

• 0.1 lt nH lt 103
• B ? 3-10 ?G, little or no dependance on density
• ? ? 0
• nH gt 103
• ? ? 2/3
• - weak B collapse not seen
• ? ? 0.4 - 0.5
• - predicted by strong magnetic field model

? ? 0.47 0.08
Crutcher (1999)
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Results for Diffuse and Molecular Clouds

• H I Clouds Molecular Clouds
• Btotal (?G) 6.0?1.8 10 3,000
• M/? lt0.25 1
• B ? ?? 0 1/2
• ?thermal 0.29 0.04
• ?turbulent 1.3 0.7

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Conclusions Observational Summary
Diffuse clouds and formation of molecular clouds

• Diffuse ISM and clouds dominated by turbulence
• ? ¼ (subcritical)

lt

• B invariance (B ? 3-10 ?G) over 4 orders of
  magnitude in density (? 10-1 to 103 cm-3)
• M/? increases to critical in molecular cores
• - gravity-driven ambipolar diffusion?
• turbulent ambipolar diffusion (Zweibel 2002,
  Heitsch et al. 2004)
• cloud formation by accumulation along field lines

B ? ?0 M/? increases
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Conclusions Observational Summary
Self-gravitating, high density molecular clouds

• Whether cloud envelopes are subcritical is unclear

• ? 1 (critical) initially in cores

• Observations are consistent with approximate
  magnetic support of molecular cores, with
  ambipolar diffusion driving star formation, on a
  fast (few free-fall times) timescale