A Chandra X-Ray View of Stephan'S Quintet: Shocks and Star Formation

We use a deep Chandra observation to examine the structure of the hot intra-group medium of the compact group of galaxies Stephan's Quintet. The group is thought to be undergoing a strong dynamical interaction as an interloper, NGC 7318b, passes through the group core at similar to 850 km s(-1). Previous studies have interpreted a bright ridge of X-ray and radio continuum emission as the result of shock heating, with support from observations at other wavelengths. We find that gas in this ridge has a similar temperature (similar to 0.6 keV) and abundance (similar to 0.3 Z(circle dot)) to the surrounding diffuse emission, and that a hard emission component is consistent with that expected from high-mass X-ray binaries associated with star formation in the ridge. The cooling rate of gas in the ridge is consistent with the current star formation rate, suggesting that radiative cooling is driving the observed star formation. The lack of a high-temperature gas component is used to place constraints on the nature of the interaction and shock, and we find that an oblique shock heating a pre-existing. lament of Hi may be the most likely explanation of the X-ray gas in the ridge. The mass of hot gas in the group is roughly equal to the deficit in observed Hi mass compared to predictions, but only similar to 2% of the gas is contained in the ridge. The hot gas component is too extended to have been heated by the current interaction, strongly suggesting that it must have been heated during previous dynamical encounters.