Far-Ultraviolet Color Gradients in Early-Type Galaxies

We discuss far-UV (1500 Å) surface photometry and FUV–B color profiles for 8 E/S0 galaxies from images taken with the Ultraviolet Imaging Telescope, primarily during the Astro-2 mission. In three cases, the FUV radial profiles are more consistent with an exponential than a de Vaucouleurs function, but there is no other evidence for the presence of a disk or of young, massive stars. In all cases except M32 the FUV–B color becomes redder at larger radii. There is a wide range of internal radial FUV–B color gradients. However, we find no correlation between the FUV–B color gradients and internal metallicity gradients based on Mg absorption features. We conclude that metallicity is not the sole parameter controlling the “UV upturn component” in old populations. Also Department of Physics and Astronomy, Johns Hopkins University, Charles and 34th Streets, Baltimore, MD 21218 Raytheon STX Corp., Lanham, MD 20706 Also Astronomy Department, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903