UNUSUAL EMISSION-LINE REGIONS IN THE TIDAL ARM OF NGC-7318B IN STEPHAN QUINTET

We report the optical spectroscopic discovery of two unusual emission- line regions in the tidal arm of a galaxy, NGC 7318B, that belongs to Stephan's Quintet. They are associated spatially with the unusual radi o continuum emission discovered between the two galaxies NGC 7318B and NGC 7319. Taking account of both the large velocity widths of the emi ssion lines, similar to 900 km s(-1) and the strong [S II] lambda lamb da 6717, 6731 emission with respect to H alpha emission, we identify t hem as optical emission-line filaments of supernova remnants (SNRs) tr aced by the radio continuum and soft X-ray emission. Our narrowband H alpha imaging shows that the unusual emission-line regions are indeed parts of the ionized bubble associated with one radio continuum peak. The required number of SNRs is estimated to be similar to 10(5)-10(6) on the basis of the H alpha, radio, and soft X-ray luminosities. Since there is no optical counterpart like a star cluster it is suggested t hat similar to 10(5)-10(6) supernova events occurred nearly simultaneo usly in this region several times 10(6) yr ago.