  Spitzer Space Telescope observations revealed powerful mid-infrared (mid-IR)
H2 rotational line emission from the Stephan's Quintet (SQ) X-ray emitting
large scale shock associated with a collision between two galaxies. Because H2
forms on dust grains, the presence of H2 is physically linked to the survival
of dust, and we expect some dust emission to come from the molecular gas. To
test this interpretation, IR observations and dust modeling are used to
identify and characterize the thermal dust emission from the shocked molecular
gas. The spatial distribution of the IR emission allows us to isolate the faint
PAH and dust continuum emission associated with the molecular gas in the SQ
shock. We model the spectral energy distribution (SED) of this emission, and
fit it to Spitzer observations. Faint PAH and dust continuum emission are
detected in the SQ shock, outside star-forming regions. The 12/24um flux ratio
in the shock is remarkably close to that of the diffuse Galactic interstellar
medium, leading to a Galactic PAH/VSG abundance ratio. However, the properties
of the PAH emission spectrum in the shock differ from that of the Galaxy, which
may suggest an enhanced fraction of large and neutrals PAHs. The IR SED is
consistent with the expected emission from dust associated with the warm
(>150K) H2 gas, heated by a UV radiation field of intensity comparable to that
of the solar neighborhood, in agreement with GALEX UV observations. The
presence of PAHs and dust grains in the high-speed (1000km/s) galaxy collision
suggests that dust survives. We propose that the dust that survived destruction
was in pre-shock gas at densites larger than a few 0.1cm-3, which was not
shocked at velocities larger than 200km/s. [abridged]
