UV color-color relation of early-type galaxies. (5th March 2015)

• Record Type: Journal Article
• Authors: Ree, Chang H.; Jeong, Hyunjin; Oh, Kyuseok; Chung, Chul; Lee, Joon Hyeop; Kim, Sang Chul; Kyeong, Jaemann
• Editors: Montmerle, Thierry
• Is Part Of: Proceedings of the International Astronomical Union. Volume 10:Number H16(2012)Highlights
• Page Start: 130
• Page End: 130
• Publication Date: 2015-03-05
• Subjects: galaxies: elliptical and lenticular, -- cD, -- galaxies: evolution, -- galaxies: stellar content; Astronomy -- Congresses; Astronomy -- Periodicals; 520
• DOI: 10.1017/S1743921314004918
• Languages: English
• ISSNs: 1743-9213

Abstract

Abstract: The ultraviolet (UV) color-color relation of early-type galaxies (ETGs) in the nearby universe (0.05 < z < 0.12) is re-examined with the latest GALEX GR6 and SDSS DR7 data. By drawing the FUV – NUV (as a measure of UV temperature) versus FUV – r (as a measure of UV amplitude) color-color diagram for the morphologically-cleaned, spectroscopically-cleaned sample of ~3700 quiescent ETGs, we find that the "old and dead" ETGs consist of a well-defined sequence in UV colors, the "UV red sequence", so that the stronger UV excess galaxies should have a harder UV spectral shape systematically. However, the observed UV spectral slope is too steep to be reproduced by the canonical models in which the UV flux is mainly controlled by age or metallicity parameters. The observed data support the helium enhancement scenario in which the UV spectral shape of UV upturn (FUV – NUV < 0.9; FUV – r ~ 6) galaxies may be governed by the minority population of helium-enhanced horizontal-branch (HB) stars.