EDP Sciences
Free access
Volume 393, Number 3, October III 2002
Page(s) 843 - 854
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20021082

A&A 393, 843-854 (2002)
DOI: 10.1051/0004-6361:20021082

The far-ultraviolet emission of early-type galaxies

J.-M. Deharveng, A. Boselli and J. Donas

Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, Les Trois Lucs, BP 8, 13376 Marseille Cedex 12, France

(Received 20 March 2002 / Accepted 12 July 2002 )

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 Mg 2 spectral line index; possible explanations are reviewed. The potential of a more extended UV survey like GALEX is briefly presented.

Key words: stars: AGB and post-AGB -- stars: horizontal-branch -- galaxies: stellar content -- galaxies: elliptical and lenticular, cD -- ultraviolet: galaxies

Offprint request: J.-M. Deharveng, jean-michel.deharveng@astrsp-mrs.fr

© ESO 2002