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

S. Kaviraj, K. Schawinski, J. E.G. Devriendt, I. Ferreras, S. Khochfar, S. J. Yoon, S. K. Yi, J. M. Deharveng, A. Boselli, T. Barlow, T. Conrow, K. Forster, P. G. Friedman, D. C. Martin, P. Morrissey, S. Neff, D. Schiminovich, M. Seibert, T. Small, T. WyderL. Bianchi, J. Donas, T. Heckman, Y. W. Lee, B. Madore, B. Milliard, R. M. Rich, A. Szalay

Research output: Contribution to journalArticlepeer-review

283 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)619-642
Number of pages24
JournalAstrophysical Journal, Supplement Series
Issue number2
Publication statusPublished - 2007 Dec

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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