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        UV-optical colors as probes of early-type galaxy evolution

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        Author
        Kaviraj, S.
        Schawinski, K.
        Devriendt, J.E.G.
        Ferreras, I.
        Khochfar, S.
        Yoon, S.-J.
        Yi, S.K.
        Lee, Y.-W.
        Deharveng, J.-M.
        Boselli, A.
        Donas, J.
        Milliard, B.
        Barlow, T.
        Conrow, T.
        Forster, K.
        Friedman, P.G.
        Martin, D.C.
        Morrissey, P.
        Seibert, M.
        Small, T.
        Wyder, T.
        Neff, S.
        Schiminovich, D.
        Bianchi, L.
        Heckman, T.
        Szalay, A.
        Madore, B.
        Rich, R.M.
        Attention
        2299/11922
        Abstract
        We have studied ∼2100 early-type galaxies in the SDSS DR3 which have been detected by the GALEX Medium Imaging Survey (MIS), in the redshift range O <z <0.1.1. Combining GALEXUV photometry with corollary optical data from the SDSS, we find that, at a 95% confidence level, at least ∼30% of galaxies in this sample have UV to optical colors consistent with some recent star formation within the last Gyr. In particular, galaxies with an NUV - r color less than 5.5 are very likely to have experienced such recent star formation, taking into account the possibility of a contribution to NUV flux from the UV upturn phenomenon. We find quantitative agreement between the observations and the predictions of a semianalytical ACDM hierarchical merger model and deduce that early-type galaxies in the redshift range 0 <z <0.11 have ∼ 1 % -3 % of their stellar mass in stars less than 1 Gyr old. The average age of this recently formed population is ∼300-500 Myr. We also find that "monolithically" evolving galaxies, where recent star formation can be driven solely by recycled gas from stellar mass loss, cannot exhibit the blue colors (NUV - r <5.5) seen in a significant fraction (∼30%) of our observed sample.
        Publication date
        2007-12-01
        Published in
        Astrophysical Journal, Supplement Series
        Published version
        https://doi.org/10.1086/516633
        Other links
        http://hdl.handle.net/2299/11922
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