(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.
