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SÉMINAIRE DU LERMA
OBSERVATOIRE DE PARIS
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Vendredi 14 juin 2002, à 14h,


77 avenue Denfert Rochereau, Paris 14



Salle de l'Atelier





MAGNETIC FIELDS IN THE DIFFUSE AND DENSE ISM



R. M. Crutcher (1) and T. H. Troland (2)

(1) Astronomy Department, University of Illinois, USA (2) Physics & Astronomy Department, University of Kentucky, USA



Résumé : Magnetic fields in the diffuse ISM are important because they can affect the dynamics of the gas, they can serve as tracers of large-scale streaming motions in the gas, and their galaxy-wide structure offers clues as to the origins of magnetic fields. Also, studies of magnetic field strengths in the diffuse ISM as a function of gas density may offer clues to the processes that cycle ISM between diffuse and dense phases. In dense regions the critical parameter for evaluating the importance of magnetic fields, especially for star formation processes, is the ratio of the mass to the magnetic flux. If this ratio is sufficiently large, the magnetic field cannot prevent gravitational collapse. Observations in dense regions focus on measuring both the field strength, from which the mass to magnetic flux ratio may be inferred, and the morphology of fields, which can also provide information about the strength of fields and their importance. Another goal of the observations is the measurement of the morphology and strengths of the uniform and random components of magnetic fields, from which the relative importance of the magnetic and turbulence energies may be inferred. In this talk we will briefly review observational techniques for measuring field morphology and strength, the results of such observations, and what our current state of knowledge about magnetic fields tells us about their importance and role in the interstellar medium and in the star formation process.