Stephan's Quintet of Interacting Galaxies

Abstract

Observations in Stephan's Quintet are reported in the following categories: (1) Location, size, and distribution of hydrogen emission regions in the different redshift systems which comprise the Quintet. (2) Light-curve and spectral data on a supernova that appeared in NGC 7319 in the year 1971. (3) Location and structure of luminous regions of the faintest recordable surface brightness which appear in the Quintet. The evidence from the H ii regions points to the conclusion that the low-redshift NGC 7320 (z = 800km s-') and the high-redshift NGC 7318 A and 13 (z = 5700 and 6700km 1) are at the same distance. That distance is indicated to be the closer distance of NGC 7320 (about 10 Mpc). The supernova in NGC 7319 appears to be Type I but is peculiar in some respects. Its estimated apparent magnitude at maximum brightness is too faint by 1.5 mag for a galaxy with a redshift of z = 6700 km s1, and very much too faint (about 6 mag) for a system of redshift z = 800 km s '. The long tail on NGC 7320, the evidence for radio interaction between NGC 7319 and NGC 7318, and the evidence for luminous hydrogen emission between NGC 7319 and both NGC 7318 and NGC 7320, however, seem to indicate that, on balance, all the members of the Quintet are interacting and are at the close (10 Mpc) distance. Subject headings: Galaxies H ii regions - redshifts supernovae