Published in "Fundamentals of Cosmic Physics", Vol. 19, pp. 1-89, 1997.

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Observations of the Magnetic Fields inside and outside the Milky Way, starting with Globules (~ 1 parsec), Filaments, Clouds, SuperBubbles, Spiral Arms, Galaxies, Superclusters, and ending with the Cosmological Universe's Background Surface (at ~ 8 Teraparsecs)

Jacques P. Vallée


Herzberg Institute of Astrophysics, National Research Council of Canada,
5071 West Saanich Road, Victoria, B.C., Canada V8X 4M6


Abstract. The observational study of galactic magnetic fields dates back to 1949; an excellent review of the early 30 years has been made by Verschuur (1979). I review here the developments since then and the current state of our observational knowledge on the magnetic fields inside and outside the Milky Way galaxy, for objects with sizes greater than 1 parsec (= 3.2 light-years; = 3.1 × 1016 m). Included are the medium-scale magnetic fields in the isolated globules, dusty elongated clouds and narrow filaments, large interstellar superbubbles, and in large-scale magnetic fields in the spiral arms in our Galaxy and in objects outside our Galaxy out to cosmological distances. The large-scale magnetic fields can act as guides to the low density gas in its motion in the rarefied areas of the interstellar medium, and as tracers of the past dynamical histories of galaxies in motion, linking galactic dynamic with galactic dynamos. Medium-scale magnetic fields can play a support role, supporting clouds against outside pressures or against collapse due to self-gravity. Small-scale magnetic fields play a significant role on smaller-scale phenomena: propagation of cosmic-rays, shock waves, cosmic dust orientation, star formation (although there is little detailed discussion here of magnetic fields on star formation and objects with sizes < 1 parsec).


Key words: Magnetic fields - Milky Way magnetism - Magnetized molecular clouds - Magnetized Superbubbles - Magnetic field and star formation - Dynamo magnetism - Magnetized galaxies - Cosmological magnetism


Table of Contents

INTRODUCTION
Review Scope and Type
Polarimetry

SELECTED CELESTIAL ZONES IN OUR GALAXY
Methodology and Techniques
Optical dust absorption
Infrared Dust Emission
Radio Zeeman Effect
Radio Faraday Rotation
Interstellar objects ( ~ 1 to 50 pc)
Excess line width Wexcess relationship with Object size R
Globules and Magnetic Fields
Narrow Magnetized Features
Magnetic field versus Gas density, on medium linear scales (B ~ n0.5)
Magnetic field shapes in Dusty Elongated Molecular Clouds
Interstellar Superbubbles and shells with B ~ n1 (~ 50 to 500 pc)
Magnetic fields and Supernovae (B ~ n1)
The Center of the Milky Way Galaxy's disk (~ 8 kpc away)

THE MILKY WAY AS A WHOLE
Magnetic fields and Interstellar Superbubbles
Magnetic fields and Spiral Arms (~ 15 kpc)
Distribution of Breg, with galactic radius
Direction of Breg
Location of zero Breg
Strength of Breg
Distribution of Bran, and strength
Larger scale view - ASS or BSS
ASS for the Milky Way
Pitfalls of the BSS model
Seeds of galactic magnetism
Primordial cosmological magnetic seeds in galaxies
Battery origin for magnetic seeds in galaxies
Recent local origins for the magnetic seeds in galaxies
Galactic Magnetic field Interpretations - dynamos or not ?
Basic notions
Future trends in Galactic Dynamos

NEARBY SPIRAL GALAXIES
Methodology - different methods to obtain the magnetic field strength
Faraday Method
Equipartition Method
Cosmic-ray Method
Comparisons
Galactic magnetic field B and star formation SF
Observed weak relationship of B with SF
Expected weak relationship of B with SF
Magnetic fields versus Gas density, on large linear scales (B ~ n0.2)
Gas density versus Star Formation
Magnetic fields in violent star-forming (starburst) galaxies
Magnetic field shape in Andromeda (M31) and other galaxies
Magnetic field B in galactic disks and neutral hydrogen HI
B shapes and HI masses
B shapes and HI shapes - companions or bars
Magnetic fields in Halos of spiral galaxies

ELLIPTICAL GALAXIES, DISTANT GALAXIES, CLUSTERS AND VOIDS, QUASARS AND COSMIC SCALES
Individual Galaxies and quasars (~ 200 kpc)
Clusters of galaxies as the largest magnets ( ~ 5 to 50 Mpc)
Several sources per individual cluster of galaxies
One source per individual cluster of galaxies
Seeds for magnetic fields in clusters of galaxies
Large Scale Voids in space (~ 100 to 200 Mpc)
Cosmological scales
Foreground Cosmological Screen (~ 20 Gigaparsecs)
Background Cosmological Surface ( ~ 8000 Gpc)

SUMMARY AND FUTURE TRENDS

REFERENCES

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