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Session 49 - Starburst Galaxies.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center
Despite its nearly edge-on configuration, observations by the Ultraviolet Imaging Telescope have shown that the interacting Sc galaxy, NGC 4631, is a copious source of far ultraviolet emission. The apparently low obscuration combined with recent intense star formation activity indicate that some sort of disturbance has stirred up the interstellar medium to large scale heights and low column densities. In particular, the super shell observed by Rand (1993, AJ, 105, 2098) at 21 cm in the eastern part of the galaxy extends approximately 2 kpc above the galactic mid- plane at far UV wavelengths. A second smaller shell several minutes to the west of the galactic center also is prominent in the far UV images. Assuming that the galaxy is at a distance of 7.5 Mpc and ignoring extinction internal to NGC 4631 we find that number of O stars required to account for the far UV luminosity observed in Rand's large and small super shells is 1500 and 1200 respectively. FUV/optical/H-alpha colors and ratios will be presented and used to infer star formation histories in all the imaged H II regions. Faint FUV emission is observed at distances up to 2.9 kpc above the galactic center. Presently, we attribute this emission to FUV light from OB stars in the disk H II regions scattered by dust in the galactic halo. An average surface brightness for this emission at 2.6 kpc above the center of the galactic disk is (1.8 \pm 0.6) \times 10^-18 ergs cm^-2 s^-1 arcsec^-2.
