The far-ultraviolet emission of early-type galaxies

We have assembled a UV-flux selected sample of 82 early-type galaxies and collected additional information at other wavelengths. These data confirm a large spread of the $UV-V$ color in the range 2 to 5. The spread in $UV-V$ is accompanied by a spread in $B-V$ that is mainly attributed to the range of morphological types and luminosities. A large fraction of the objects have red colors, $UV-V = 4 \pm 0.4$, corresponding to a weak UV-upturn as observed with IUE. If the current interpretation for the UV emission from early-type galaxies is applicable to our sample, the PAGB (Post-Asymptotic Giant Branch) tracks are the most common evolution path for the low-mass stars responsible for the UV emission. A small number of very blue ($UV-V < 1.4$) objects have been found that can be reasonably interpreted as harbouring some low level of star formation. In contrast to a previous sample based on IUE observations, no correlation is found between the $UV-V$ color and the Mg2 spectral line index; possible explanations are reviewed. The potential of a more extended UV survey like GALEX is briefly presented