Powering The Intra-cluster Filaments in Cool-Core Clusters of Galaxies
  The first radio surveys of the sky discovered that some large clusters of
galaxies contained powerful sources of synchrotron emission. Optical images
showed that long linear filaments with bizarre emission-line spectra permeated
the intra-cluster medium. Recent observations in the infrared and radio show
that these filaments have very strong emission lines of molecular hydrogen and
carbon monoxide. The mass of molecular material is quite large, the gas is
quite warm, and the filaments have not formed stars despite their ~Gyr age. I
will discuss the general astrophysical context of large clusters of galaxies
and how large masses of molecular gas can be heated to produce what we observe.
  The unique properties of the filaments are a result of the unique
environment. Magnetically confined molecular filaments are surrounded by the
hot intra-cluster medium. Thermal particles with keV energies enter atomic and
molecular regions and produce a shower of secondary nonthermal electrons. These
secondaries collisionally heat, excite, dissociate, and ionize the cool gas.
While ionization is dominated by these secondary particles, recombination is
controlled by charge exchange, which produces the unusual optical emission line
spectrum. I will describe some of the physical processes that are unique to
this environment and outline some of the atomic physics issues.
