Powerful H2 Line Cooling in Stephan's Quintet II. Group-wide Gas and
  Shock Modeling of the Warm H2 and a Comparison with [CII]157.7um Emission and
  Kinematics
  We map for the first time the two-dimensional H_2 excitation of warm
intergalactic gas in Stephan's Quintet on group-wide (50 x 35 kpc^2) scales to
quantify the temperature, mass and warm-H_2 mass fraction as a function of
position using Spitzer. Molecular gas temperatures are seen to rise (to T >
700K) and the slope of the power--law density-temperature relation flattens
along the main ridge of the filament, defining the region of maximum heating.
We also performed MHD modeling of the excitation properties of the warm gas, to
map the velocity structure and energy deposition rate of slow and fast
molecular shocks. Slow magnetic shocks were required to explain the power
radiated from the lowest--lying rotational states of H_2, and strongly support
the idea that energy cascades down to small scales and low velocities from the
fast collision of NGC 7318b with group-wide gas. The highest levels of heating
of the warm H_2 is strongly correlated with the large-scale stirring of the
medium as measured by [CII] spectroscopy with Herschel. H_2 is also seen
associated with a separate bridge which extends towards the Seyfert nucleus in
NGC 7319, both from Spitzer and CARMA CO observations. This opens up the
possibility that both galaxy collisions and AGN outflows can turbulently heat
gas on large-scales in compact groups. The observations provide a laboratory
for studying the effects of turbulent energy dissipation on group-wide scales
that may provide clues about the heating and cooling of gas at high-z in early
galaxy and protogalaxy formation.
