Stephan’s Quintet: The X-ray Anatomy of a Multiple Galaxy Collision

Chandra observations of the compact galaxy group known as Stephan’s Quintet (SQ) are presented. The major morphological features that were discovered with the ROSAT HRI are now imaged with higher resolution and S/N. The large scale shock (1.′5, ∼40kpc if at 85 Mpc) is resolved into a narrow NS feature embedded in more extended diffuse emission (D≥ 3′). The NS structure is somewhat clumpy, more sharply bounded on the W side and prominent only in the soft band (energies below ∼ 2 keV). Its observational properties are best explained as a shock produced by a high velocity encounter between NGC 7318b, a “new intruder”, and the intergalactic medium in SQ. The shock conditions near the high speed intruder suggest that a bow shock is propagating into a pre-existing H i cloud and heating the gas to a temperature of 0.5 keV. The low temperature in the shock is a problem unless we postulate an oblique shock. One member, NGC 7319, hosts a Seyfert 2 nucleus, with an intrinsic luminosity LX= 10 43 erg s, embedded in a region of more diffuse emission with 10′′ radius extent. The nuclear spectrum can be modeled with a strongly absorbed power-law typical of this class of sources. Several additional compact sources are detected including three in foreground NGC 7320. Some of these sources are very luminous and could be related to the ultraluminous X-ray sources found in nearby galaxies.