SIMULATED OPTICAL-IMAGES OF GALAXIES AT Z-APPROXIMATELY 1 USING ULTRAVIOLET IMAGES OF NEARBY GALAXIES

Ultraviolet sounding rocket images of several nearby galaxies are used to simulate the appearance in optical bandpasses of similar systems at redshifts z = 0.5-2.67, as observed by the WFPC on HST and by ground-based instruments. Since the morphology of galaxies is a strong function of the wavelength, the appearance of galaxies at large redshifts is subject to a large k-correction effect. The strong dependence of monochromatic surface brightness on redshift [I-lambda approximately (1 + z)-5] also implies that observed morphology of distant systems will be crucially dependent on the limiting surface brightness set by the sky background. Although the angle sub-tended by sources depends only weakly on z, the fraction of a galaxy whose surface brightness is above the detection threshold varies strongly with z. Morphological distinctions of spiral from elliptical, spiral from irregular, and barred from unbarred types become more difficult, as does accurate evaluation of interactions or of the local environment.