Magnetic fields in our Milky Way Galaxy and nearby galaxies
  Magnetic fields in our Galaxy and nearby galaxies have been revealed by
starlight polarization, polarized emission from dust grains and clouds at
millimeter and submillimeter wavelength, the Zeeman effect of spectral lines or
maser lines from clouds or clumps, diffuse radio synchrotron emission from
relativistic electrons in interstellar magnetic fields, and the Faraday
rotation of background radio sources as well as pulsars for our Milky Way. It
is easy to get a global structure for magnetic fields in nearby galaxies, while
we have observed many details of magnetic fields in our Milky Way, especially
by using pulsar rotation measure data. In general, magnetic fields in spiral
galaxies probably have a large-scale structure. The fields follow the spiral
arms with or without the field direction reversals. In the halo of spiral
galaxies magnetic fields exist and probably also have a large-scale structure
as toroidal and poloidal fields, but seem to be slightly weaker than those in
the disk. In the central region of some galaxies, poloidal fields have been
detected as vertical components. Magnetic field directions in galaxies seem to
have been preserved during cloud formation and star formation, from large-scale
diffuse interstellar medium to molecular clouds and then to the cloud cores in
star formation regions or clumps for the maser spots. Magnetic fields in
galaxies are passive to dynamics.
