X-RAY-IMAGING SPECTROSCOPY OF STEPHANS QUINTET AND SEYFERT-2 GALAXY NGC-7319

We observed Stephan's Quintet, a compact group of galaxies, with the J apanese X-ray satellite ASCA. The ASCA observation has revealed that t he X-ray emission consists of two components. One is a soft X-ray emis sion characterized by thin thermal model with kT = 0.76(-0.10)(+0.05) keV and a metal abundance of 0.08 +/- 0.04 solar. Since the soft X-ray s are extended and the centroid is located at the region between NGC 7 318 and NGC 7319, thin thermal emission originates from diffuse hot ga s filling the Quintet. The total mass of hot gas is about 2 x 10(10)M( .), which is only 10% of the galaxy mass. The low metal abundance indi cates that most of the hot gas consist of primordial gas. The binding mass is about 6 x 10(12)M(.). The baryonic fraction is about 10%. The other component is hard X-ray emission located at NGC 7319, a Seyfert 2 galaxy. The X-ray spectrum is well fitted by the absorbed-power law emission plus a line. The photon index is 0.8(-1.1)(+0.8), and the abs orption column is about 10(23) cm(-2). The X-ray luminosity in the 2-1 0 keV band is about 1.7 x 10(42) erg s(-l). These characteristics are consistent with those of Seyfert 2 galaxies. We have revealed an obscu red nucleus in NGC 7319. Our results well explain the flux of Ha and a nisotropic radiation seen in the optical band.