An understanding of the empirical correlation between the strength of the UV upturn and the metallicity of luminous elliptical galaxies (Burstein and coworkers) is vital in the study of the evolution of elliptical galaxies. We support a modestly old (15-20 Gyr), metal-rich hypothesis ([Fe/H] 5 0) for the UV sources in UV upturn galaxies as an alternative to the old (520 Gyr), metal-poor ([Fe/H] = —1.0) hypothesis of Park Lee. This preliminary result of our population synthesis is based on a Gaussian mass distribution on the horizontal branch and a complete library of stellar evolution tracks, both of which are crucial in producing UV light in the metal-rich systems. The metal-rich hypothesis has an advantage over the metal-poor one not only because it explains the UV upturn-metallicity relation but also because it requires neither an uncomfortably large age nor a large age span for elliptical galaxies. We suggest several observational tests to constrain the metallicity of the UV sources. Subject headings: Galaxies: Elliptical and lenticular, cD — galaxies: evolution — ultraviolet: galaxies.
Bibliographical noteFunding Information:
We thank R. Larson for useful comments, I. Hubeny for letting us use his non-LTE spectral synthesis code, and R. Kurucz for providing us with his model atmospheres. We are also grateful to the anonymous referee for useful comments and questions. This research was supported by NASA grant NAGW-2937 to Yale University.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science