Abstract
This article describes how interstellar magnetic fields are detected, measured, and mapped, the results of such observations, and the role played by interstellar magnetic fields in the physics of the interstellar medium. A goal of the observations is the measurement of the morphology and strengths of the uniform (B u) and random (B r) components of magnetic fields. Observational techniques probe either the component of B parallel to the line of sight (B‖) or in the plane of the sky (B⊥). Tracers of B‖ are Faraday rotation of the position angle of linearly polarized radiation and Zeeman splitting of spectral lines. Tracers of B⊥ are the strength of synchrotron radiation and linear polarization of synchrotron radiation and of emission or absorption from dust and spectral lines. Starlight polarization shows that on large spatial scales the Galactic magnetic field is not heavily tangled (B u/B r ≈ 0.7-1.0), that the field is generally parallel to the Galactic plane near the plane, that the local field points approximately along the local spiral arm (pitch angle 9.4°, center of curvature 7.8 kpc distant towards ℓ≈15.4;°), and that off the Galactic plane there is considerable small-scale structure to the field. Galactic synchrotron emission shows magnetic spiral arms with a total strength Bt ≈6 μG and B u ≈ 4 μG. Pulsar data show evidence for reversals of the field direction with Galactic radius and yield Br ≈ 5 μG and B u ≈ 1.5 μG; the morphology of the largescale mean field is consistent with dynamo generation. H I Zeeman detections for diffuse clouds yield B‖ ∼ 5;–20 μG with many limits B‖< 5 μG. A recent survey of Galactic H I in absorption against extragalactic sources confirms the result that the fields in diffuse clouds are often quite weak. The critical parameter for evaluating the importance of magnetic fields in star formation is the ratio of the mass to the magnetic flux, M/ΦB; observations focus on measuring both this quantity and the morphology of fields in dense regions. Zeeman observations of molecular lines are consistent with B ασv√n, which is the theoretical prediction for flattened cores supported by a combination of a uniform magnetic field pressure and turbulence. In cores, motions are approximately Alfvénic, and M/ΦB has a critical to slightly supercritical value. The ratio of B r/B u appears to decline with density. In some molecular cores there is evidence for the “hourglass” pinch that would be produced by cloud contraction with the magnetic field frozen into the matter.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Preview
Unable to display preview. Download preview PDF.
References
S. Basu: ApJ 540, L103 (2000)
R. Beck: Space Science Reviews 99, 243 (2001)
T. L. Bourke, P. C. Myers, G. Robinson, A. R. Hyland: ApJ 554, 916 (2001)
J. C. Brown, A. R. Taylor: ApJ 563, L31(2001)
C. Chandler, J.E. Carlstrom: ApJ 466, 338 (1996)
S. Chandrasekhar, E. Fermi: ApJ 118, 113 (1953)
G. E. Ciolek, S. Basu: ApJ 529, 925 (2000)
R. M. Crutcher: ApJ 234, 881 (1979)
R.M. Crutcher, T. H. Troland, A. A. Goodman, C. Heiles, I. Kazes, P. C. Myers: ApJ 407, 175 (1993)
R. M. Crutcher, T. Troland, B. Lazare., G. Paubert, I. Kazes: ApJ 514, l121 (1999)
R.M. Crutcher: ApJ 520, 706 (1999)
R. M. Crutcher, T. H. Troland: ApJ 537, L139 (2000)
J. Davis, J. L. Greenstein: ApJ 114, 206 (1951)
B. Draine: ‘Electromagnetic Properties of Grains Related to Grain Alignment’. In: Polarimetry of the Interstellar Medium, A.S.P. Conference Series Volume 97, ed. By W.G. Roberge, D.C.B. Whittet(ASP, San Francisco 1996) pp. 16
J.D. Fiege, R.E. Pudritz: MNRAS 311, 85 (2000)
J.D. Fiege, R.E. Pudritz: MNRAS 311, 105 (2000)
T. Gold: Nature 169, 322 (1951)
P. Goldreich, N.D. Kylafis: ApJ 243, 75 (1981)
A. A. Goodman, T. J. Jones, E.A. Lada, P. C. Lada: ApJ, 448, 748 (1995)
J.L. Han, R.N. Manchester, E.M. Berkhuijsen, R. Beck: A &Ap, 322, 98 (1997)
J.L. Han, R.N. Manchester, G.J. Qiao: MNRAS 306, 371 (1999)
J.L. Han: ‘Magnetic fields in our Galaxy: How much do we know? (II) Halo fields and the flobal field structure’. In: Astrophysical Polarized Backgrounds, American Institute of Physics Conference Proceedings 609, ed. by S. Cecchini, S. Cortiglioni, R. Sault, C. Sbarra (AIP, 2002), pp. 96
C. Heiles, W. T. Reach, B. Koo: ApJ, 466, 191 (1996)
C. Heiles: ApJ, 462, 316 (1996)
C. Heiles: ‘A Comprehensive View of the Galactic Magnetic Field, Especially near the Sun’. In: Polarimetry of the Interstellar Medium, A.S.P. Conference Series Volume 97, ed. By W.G. Roberge, D.C.B. Whittet (ASP, San Francisco 1996) pp. 457
C. Heiles: AJ, 119, 923 (2000)
C. Heiles: PASP 113, 788 (2001)
C. Heiles: ApJ 551, L105 (2001)
C. Heiles, T. Troland: to be submitted to ApJ (2002)
F. Heitsch, E.G. Zweibel, M.-M. MacLow, P.S. Li, M.L. Norman: ApJ 561, 800 (2001)
R. H. Hildebrand, J. A. Davidson, J. L. Dotson, C. D. Dowell, G. Novak, J. E. Vaillancourt: PASP, 112, 1215 (2000)
C. Indranin, A.A. Deshpande: New Astronomy, 4, 33 (1998)
N.D. Kylafis: ApJ 275, 135 (1983)
S.-P. Lai, University of Illinois Ph.D. thesis (2001)
A. Lazarian: ‘Gold Alignment’. In: Polarimetry of the Interstellar Medium, A.S.P. Conference Series Volume 97, ed. By W.G. Roberge, D.C.B. Whittet (ASP, San Francisco 1996) pp. 433
A. Lazarian, A. A. Goodman, P. C. Myers: ApJ 490, 273 (1997)
B. C. Matthews, C. D. Wilson, J. D. Fiege: ApJ 562, 400 (2001)
C.F. McKee: ‘The Dynamical Structure and Evolution of Giant Molecular Clouds’. In: The Origin of Stars and Planetary Systems, ed. by C.J. Lada, N.D. Kylafis (Kluwer, Dordrecht 1999) pp. 29–66
C. F. McKee, E. G. Zweibel: ApJ 399, 551 (1992)
T.Ch. Mouschovias, L. Spitzer, Jr.: ApJ 210, 326 (1976)
T.Ch. Mouschovias, G.E. Ciolek: In: The Origin of Stars and Planetary Systems. ed. by C.J. Lada & N.D. Kylafis (Kluwer, Dordrecht 1999) pp. 305–340
P. Myers, A.A. Goodman: ApJ 329, 392 (1988)
E.C. Ostriker, J.M. Stone, C.F. Gammie: ApJ 546, 980 (2001)
P. Padoan, A. Goodman, B. T. Draine, M. Juvela, A. Nordlund, O. E. Rognvaldsson: ApJ 559, 1005 (2001)
R. Rao, R. M. Crutcher, R. L., Plambeck, M. C. H. Wright: ApJ 502, L75 (1998)
D.A. Schleuning: ApJ 493, 811 (1998)
F.H. Shu, A. Allen, H. Shang, E.C. Ostriker, Z.-Y. Li: In: The Origin of Stars and Planetary Systems. ed. by C. J. Lada & N. D. Kylafis (Kluwer, Dordrecht 1999) pp. 193–226
T. H. Troland, R. M. Crutcher, A. A. Goodman, C. Heiles, I. Kazes, P. C. Myers: ApJ 471, 302 (1996)
B. E. Turner, R. H. Gammon: ApJ 198, 71 (1975)
J.M. Walawender, E.G. Zweibel, C. Heiles: ApJ, in preparation (2002)
W. D. Watson, D. S. Wiebe, R. M. Crutcher: ApJ 549, 377 (2001)
D. S. Wiebe, W. D. Watson: ApJ 549, L115 (2001)
D.A. Weintraub, A.A. Goodman, R.L. Akeson In ‘Protostars and Planets IV’. ed. V. Mannings, A.P. Boss & S.S. Russell (University of Arizona Press), in press
D. P. Woody, S. L. Scott, N. Z. Scoville, L. G. Mundy, A. I. Sargent, S. Padin, C. G. Tinney, C. D. Wilson: ApJ 337, L41 (1989)
E.G. Zweibel, C. Heiles: Nature 385, 131 (1997)
Author information
Authors and Affiliations
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2003 Springer-Verlag Berlin Heidelberg
About this chapter
Cite this chapter
Crutcher, R., Heiles, C., Troland, T. (2003). Observations of Interstellar Magnetic Fields. In: Falgarone, E., Passot, T. (eds) Turbulence and Magnetic Fields in Astrophysics. Lecture Notes in Physics, vol 614. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-36238-X_6
Download citation
DOI: https://doi.org/10.1007/3-540-36238-X_6
Published:
Publisher Name: Springer, Berlin, Heidelberg
Print ISBN: 978-3-540-00274-1
Online ISBN: 978-3-540-36238-8
eBook Packages: Springer Book Archive