The impact of IUE observations on our knowledge about galaxies and quasars

Observations of extragalactic objects with IUE are discussed. Elliptical galaxies show the presence of very hot stars which are probably highly evolved horizontal branch objects, although the observations are not adequate to rule out young OB stars. Spiral and irregular galaxies often show evidence of young OB stars although the nucleus of M31 is very similar to elliptical galaxies. Several narrow emission line galaxies appear to have nonthermal continua. Observations of Seyfert galaxies permit detailed studies of the continua and line ratios such as L alpha to H beta to be made. Unlike quasars, there is evidence for dust based on the 2175 A feature. The problem of understanding Seyfert galaxy spectra is no easier than that for quasars although observed variability in the broad lines may present useful clues. Observations of high redshift quasars with IUE allow spectra to be obtained down to rest wavelengths of a few hundred Angstroms and provide information about the amount of ionizing flux. Observations of low redshift quasars can be used to test whether the myriads of absorption lines seen below L alpha in high redshift quasars are indeed produced by intergalactic clouds and halos of intervening galaxies.