October 23, 1997 CfA Colloquium


Title: Magnetic Fields in Galactic Nuclei

Speaker: Mark Morris, UCLA

Abstract: If the magnetic field in the central few hundred parsecs of our Galaxy is any guide, then the field strengths in spiral galaxy nuclei are as much as three orders of magnitude higher than those in the disks, and they have to be considered in the evaluation of dynamical phenomena, nuclear activity, star formation, and the pressure balance of the nuclear interstellar medium. The evidence for such a strong field in the Milky Way comes from radio observations of synchrotron filaments which are remarkably uniform and undistorted over scales of tens of parsecs, and from direct observations of the polarization of thermal emission from magnetically aligned dust grains in molecular clouds. The geometry of the field is apparently highly ordered both inside and outside of dense clouds, but it is dramatically different in the two environments. This observation supports a model wherein molecular clouds play a central role in generating the nonthermal radio filaments via magnetic reconnection at their fortuitously ionized surfaces. The origin of the fields in both environments will be discussed, and arguments for a primordial origin for the pervasive intercloud field will be presented. The same considerations apply to all disk galaxies, so the conclusions may be widely generalizable, although observations of other galaxies are still in a relatively primitive state.

Reference for students: Get 1996 Annual Review (vol 34) paper "The Galactic Center Environment" from Jean Collins.