UV properties of early-type galaxies in the Virgo Cluster

© 2005. The American Astronomical Society. All rights reserved. We thank an unknown referee for his/her criticism. GALEX (Galaxy Evolution Explorer) is a NASA Small Explorer, launched in 2003 April. We gratefully acknowledge NASA’s support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d’Etudes Spatiales of France and the Korean Ministry of Science and Technology. The authors would like to take this opportunity to thank the members of the GALEX SODA team for their valiant efforts in the timely reduction of the complex observational data set covering the full expanse of the Virgo Cluster.
We study the UV properties of a volume-limited sample of early-type galaxies in the Virgo Cluster combining new GALEX far-ultraviolet (1530 Å) and near-ultraviolet (2310 Å) data with spectrophotometric data available at other wavelengths. The sample includes 264 elliptical, lenticular, and dwarf galaxies spanning a large range in luminosity (M_B ≤ -15). While the NUV to optical or near-IR color-magnitude relations (CMRs) are similar to those observed at optical wavelengths, with a monotonic reddening of the color index with increasing luminosity, the (FUV - V) and (FUV - H) CMRs show a discontinuity between massive and dwarf objects. An even more pronounced dichotomy is observed in the (FUV - NUV) CMR. For elliptical galaxies, the (FUV - NUV) color becomes bluer with increasing luminosity and with increasing reddening of the optical or near-IR color indices. For the dwarfs, the opposite trend is observed. These observational evidences are consistent with the idea that the UV emission is dominated by hot, evolved stars in giant systems, while in dwarf ellipticals residual star formation activity is more common.
Depto. de Física de la Tierra y Astrofísica
Fac. de Ciencias Físicas
TRUE
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