New insights on Stephan's Quintet: exploring the shock in three   dimensions
  We carried out IFU optical spectroscopy on three pointings in and near the SQ shock. We used PMAS on the 3.5m Calar Alto telescope to obtain measures of emission lines that provide insight into physical properties of the gas. Severe blending of H\alpha\ and [NII]6548,6583A emission lines in many spaxels required the assumption of at least two kinematical components in order to extract fluxes for the individual lines. Main results from our study include: (a) detection of discrete emission features in the new intruder velocity range 5400-6000km/s showing properties consistent with HII regions, (b) detection of a low velocity component spanning the range 5800-6300km/s with properties resembling a solar metallicity shocked gas and (c) detection of a high velocity component at ~6600km/s with properties consistent with those of a low metallicity shocked gas. The two shocked components are interpreted as products of a collision between NGC7318b new intruder and a debris field in its path. This has given rise to a complex structure of ionized gas where several components with different kinematical and physical properties coexist although part of the original ISM associated with NGC7318b is still present and remains unaltered. Our observations suggest that the low velocity ionized component might have existed before the new intruder collision and could be associated with the NW-LV HI component of Williams et al. (2002). The high velocity ionized component might fill the gap between the HI complexes observed in SQ-A and NGC7319's tidal filament (NW-HV, Arc-N and Arc-S in Williams et al. 2002). 
J. Iglesias-P\'aramo (1,2), L. L\'opez-Mart\'in (3,4), J. M. V\'ilchez   (1), V. Petropoulou (1) and J. W. Sulentic (1) ((1)...
astro-ph.CO astro-ph.GA