The far-ultraviolet emission of early-type galaxies (original) (raw)

A&A 393, 843-854 (2002)

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

Corresponding author: J.-M. Deharveng, jean-michel.deharveng@astrsp-mrs.fr

Received: 20 March 2002
Accepted: 12 July 2002

Abstract

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.

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

© ESO, 2002

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