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

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

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

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

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

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

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

L1544 Starless Core n(H 2 )  5  10 5 cm -3, N(H 2 )  4  10 22,   13 , B pos  140  G, c  0.8 Crutcher et al. (2004)

L1544 Starless Core Crutcher & Troland (2000) n(H 2 )  5  10 5 cm -3, N(H 2 )  4  10 22,   13 , B pos  140  G, c  0.8 Crutcher et al. (2004) n(H 2 )  1  10 4, N(H 2 )  9  10 21, B los = 11 µG, c  1.1

L183 & L1498 Starless Cores n(H 2 )  3  10 5, N(H 2 )  3  10 22,   13 , B pos  80 µG, c  0.9 Crutcher et al. (2004) Kirk & Crutcher (2005) L183L1498   40 

NGC1333 IRAS4 (BIMA 230 GHz) Girart et al. (1999) B pos > 1 mG

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

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

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 DR21(OH) # of positions  21 –  10

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

DR21(OH) 1.CO polarization: n(H 2 ) ~ 10 2, B pos  0.01 mG 2.Dust polarization & CN Zeeman: n(H 2 ) ~ 10 6, N(H 2 )  3  B pos  B los  0.7 mG, c  1.1 Combining 1 and 2, B   0.45

The Orion Molecular Cloud

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

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

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

Orion Molecular Cloud Girart et al. 2004

Orion Molecular Cloud Girart et al. 2004

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

W3OH CN Zeeman, B los =1.1 mG Turner & Welch 1984Falgarone, Crutcher, & Troland 2005

W3OH Gusten et al mG n(H 2 )  6  10 6, N(H 2 )  5  10 23, B los  3.1 mG, c  0.5

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

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

Conclusions for Molecular Cores 1.B   0, n < 10 3  molecular clouds form by accumulation along B 2.Magnetic fields usually not tangled  B dominates turbulence 3.Hourglass B morphology on cores  magnetic support 4.M/  ~ critical in molecular cores  magnetic support 5.B   ,    2/3  magnetic support

Dust Polarization and the CBM Arce, et al 1998

Molecular Cirrus Desert, Bazell, & Boulanger 1988 Stark 1995

Some Telescopes Used for Study of B

Coming Telescope for Study of B