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Magnetic Fields in Molecular Clouds Richard M. Crutcher University of Illinois

Magnetic Fields in Molecular Clouds Richard M. Crutcher University of Illinois Collaborators: Tom Troland, University of Kentucky Edith Falgarone, Ecole Normale Superieure Shih-Ping Lai, University of Maryland Ramprasad Rao, SubMillimeter Array Paulo Cortes, University of Illinois

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Magnetic Fields in Molecular Clouds Richard M. Crutcher University of Illinois

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  1. Magnetic Fields in Molecular Clouds Richard M. Crutcher University of Illinois Collaborators: Tom Troland, University of Kentucky Edith Falgarone, Ecole Normale Superieure Shih-Ping Lai, University of Maryland Ramprasad Rao, SubMillimeter Array Paulo Cortes, University of Illinois Jason Kirk, University of Illinois Doug Roberts, Northwestern University Josep Girart, University of Barcelona

  2. Outline of Talk • possible roles of magnetic fields • important parameters • observational techniques • observational result exemplars • conclusions • implications for study of CMB polarization • the future

  3. Possible Roles of Magnetic Fields • formation of molecular clouds • fragmentation to form cores • support against collapse • transport of angular momentum • from central regions of cores, • enabling star formation

  4. Field Morphology • Strong B, magnetic support implies: • non-tangled (smooth) field lines • hourglass morphology Shu, The Physical Universe (1982)

  5. Mass-to-Flux Ratio: M/ mass/flux ratio  gravitational collapse / magnetic support • Uniform disk Nakano & Nakamura (1978) critical subcritical  • Observing M/ supercritical •  definition • Geometry correction Ciolek & Mouschovias (1994)

  6. Scaling of B with : B   B  0 B  1 Spherical collapse (weak magnetic fields) Magnetic support, ambipolar diffusion • flux freezing: M   • mass conservation: B  0.4 Mestel (1966) Ciolek & Mouschovias (1994)

  7. Observational Techniques 1. Zeeman effect V  [dI/d] Blos Q,U  [dI/d]2 Bpos • 2. Polarization of dust emission •  linear polarization B  morphology of Bpos •  indirectly (Chandrasekhar & Fermi): •  Bpos  0.5(4)1/2Vlos / • 3. Goldreich-Kylafis effect •  anisotropic radiation field  non-LTE magnetic sublevels •  linear polarization or B  morphology of Bpos •  Chandrasekhar-Fermi may be applied to estimate Bpos

  8. L1544 Starless Core n(H2)  5  105 cm-3, N(H2)  4  1022,   13, Bpos 140 G, c  0.8 Crutcher et al. (2004)

  9. L1544 Starless Core n(H2)  1  104, N(H2)  9  1021, Blos= 11µG, 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)

  10. L183 & L1498 Starless Cores L183 L1498 Crutcher et al. (2004) Kirk & Crutcher (2005) n(H2)  3  105, N(H2)  3  1022,   13,Bpos 80µG, c  0.9   40

  11. NGC1333 IRAS4 (BIMA 230 GHz) Girart et al. (1999) Bpos > 1 mG

  12. NGC1333 IRAS4 (SMA 345 GHz) Rao, Girart and Marrone

  13. DR21(OH) Blos = 0.4, 0.7 mG Lai et al. (2003) Crutcher et al. (1999)

  14. DR21(OH) • Linearly Polarized J=2-1 and J=1-0 Lines • J=2-1 polarization is perpendicular to dust polarizaton and therefore parallel to the magnetic field • J=1-0 polarization is • orthogonal to J=2-1 • polarization! • requires two sources of anisotropic CO excitation • anisotropic velocity gradient (and ), and photon trapping • IR from compact dust cores 6 # of positions 4 2 50 70 90 110 21 – 10

  15. DR21(OH) Cortes, Crutcher, & Watson (2005)

  16. DR21(OH) 1. CO polarization: n(H2) ~ 102, Bpos  0.01 mG 2. Dust polarization & CN Zeeman: n(H2) ~ 106, N(H2)  3  1023 Bpos Blos0.7 mG, c  1.1 Combining 1 and 2, B  0.45

  17. The Orion Molecular Cloud

  18. NGC 2024 (Orion B) Magnetic Field Maps Crutcher et al. (1999)

  19. NGC 2024 (Orion B) Lai, Crutcher, et al.(2001)

  20. NGC 2024 SCUBA Dust Polarization Matthews et al. (2002)

  21. Orion Molecular Cloud Girart et al. 2004

  22. Orion Molecular Cloud Girart et al. 2004

  23. Orion Molecular Cloud Houde et al. 2004 Rao et al. 1998

  24. W3OH CN Zeeman, Blos =1.1 mG Turner & Welch 1984 Falgarone, Crutcher, & Troland 2005

  25. W3OH 8-11 mG n(H2)  6  106, N(H2)  5  1023, Blos 3.1 mG, c  0.5 Gusten et al. 1994

  26. Mass to Magnetic Flux Ratios mass/flux ratio ()  gravitational collapse /magnetic support H I clouds, subcritical!

  27. Field Strength vs. Density B   Weak B  = 2/3 Strong B   0.4   0.47 ± 0.08

  28. Conclusions for Molecular Cores • B  0, n < 103 • molecular clouds form • by accumulation alongB • Magnetic fields usually not tangled •  B dominates turbulence • Hourglass B morphology on cores •  magnetic support • M/ ~ critical in molecular cores •  magnetic support • B  ,   0.4-0.5  2/3 •  magnetic support

  29. Dust Polarization and the CBM Arce, et al 1998

  30. Molecular Cirrus Desert, Bazell, & Boulanger 1988 Stark 1995

  31. Some Telescopes Used for Study of B

  32. Coming Telescope for Study of B

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