Far-ultraviolet imagery of the edge-on spiral galaxy NGC 4631

Far-ultraviolet (FUV) imagery of the edge-on, Sc/SBd galaxy NGC 4631 reveal s very strong FUV emission, resulting from active star formation, uniformly distributed along the galactic midplane. Multiband imagery, H I and H II p osition-velocity curves, and extinction considerations all imply that the e mission is from the outer edges of the visible galaxy. The overall FUV morp hology of this edge-on disk system is remarkably similar to those of the "c hain galaxies" evident at high redshift, thus suggesting a similar interpre tation for at least some of those distant objects. FUV, U, B, and V magnitu des, measured for 48 star-forming regions, along with corresponding H alpha and H beta measurements are used to construct diagnostic color-color diagr ams. Although there are significant exceptions, most of the star-forming re gions are less massive and older than 30 Doradus. Comparison with the expec tations from two star formation models yields ages of 2.7 to 10 Myr for the instantaneous burst (IB) model and star formation cutoff ages of 0 to 9 My r for the continuous star formation (CSF) model. Interpreted in terms of th e IB model the photometry implies a total created mass in the 48 star-formi ng regions of 2.5 x 10(7) M-.. When viewed as resulting from constant star formation the photometry implies a star formation rate of 0.33 M-. yr(-1). These results are compared to those derived from FIR and radio observations . Corrections for FUV emission reprocessed by interstellar grains are estim ated. A large ring, similar to3 kpc in diameter, of 14 star-forming regions is concentrically located with an expanding H I shell toward the eastern e nd of the galaxy. Our observations imply that the shell may have been gener ated primarily by supernovae arising from 5.3]10(4) OB stars in a massive s tar-forming region beginning about 20 Myr ago, and that the presently obser ved FUV bright emission is due to second generation stars.