2001AJ....122.2993S

Stephan's Quintet (SQ) is a compact group that we find in an atypical moment when a high-velocity intruder is passing through it. The intrusion is particularly interesting because a previous intruder had stripped most of the gas from the group members. This debris field was shocked in the ongoing collision with the new intruder. This evolutionary history agrees well with observations and explains how a strongly interacting system can show low levels of star formation. We present new multiwavelength data including previously unpublished ROSAT X-ray, Hα interference filter/Fabry-Pérot, ISO MIR/FIR, and radio line and continuum images. These observations and previously published data provide new insights, as well as support for some previous hypotheses. (1) Fabry-Pérot and H I velocities allow us to unambiguously distinguish between gas associated with SQ and the new intruder. (2) Most detected emission regions are found in the remnant interstellar medium (ISM) of the new intruder, which allows us to infer its size and present physical state. (3) The few emission regions associated with the stripped ISM of SQ include the best candidate tidal dwarf galaxy. (4) Multiwavelength data suggest that strong MIR/FIR emission from the Seyfert 2 nucleus of NGC 7319 comes from dust heated directly by a power-law continuum rather than a starburst. (5) The correspondence between extended X-ray/radio continuum/forbidden optical emission confirms the existence of a large scale shock in SQ. (6) We confirm the presence of two stripped spiral members in the process of transformation into E/S0 morphology. Finally (7) observations are consistent with the idea that the collision in SQ is ongoing with possible detection of H II region ablation and Rayleigh-Taylor instabilities.