Pahs, Ionized Gas, and Molecular Hydrogen in Brightest Cluster Galaxies
  of Cool Core Clusters of Galaxies
  We present measurements of 5-25 {\mu}m emission features of brightest cluster
galaxies (BCGs) with strong optical emission lines in a sample of 9 cool-core
clusters of galaxies observed with the Infrared Spectrograph on board the
Spitzer Space Telescope. These systems provide a view of dusty molecular gas
and star formation, surrounded by dense, X-ray emitting intracluster gas. Past
work has shown that BCGs in cool-core clusters may host powerful radio sources,
luminous optical emission line systems, and excess UV, while BCGs in other
clusters never show this activity. In this sample, we detect polycyclic
aromatic hydrocarbons (PAHs), extremely luminous, rotationally-excited
molecular hydrogen line emission, forbidden line emission from ionized gas ([Ne
II] and [Ne III]), and infrared continuum emission from warm dust and cool
stars. We show here that these BCGs exhibit more luminous forbidden neon and H2
rotational line emission than star-forming galaxies with similar total infrared
luminosities, as well as somewhat higher ratios of 70 {\mu}m / 24 {\mu}m
luminosities. Our analysis suggests that while star formation processes
dominate the heating of the dust and PAHs, a heating process consistent with
suprathermal electron heating from the hot gas, distinct from star formation,
is heating the molecular gas and contributing to the heating of the ionized gas
in the galaxies. The survival of PAHs and dust suggests that dusty gas is
somehow shielded from significant interaction with the X-ray gas.
