Age derivation from UV absorption indices and the effect of the UV upturn

Claire Le Cras*, Claudia Maraston, Daniel Thomas

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We exploit stellar population models of absorption features in the ultraviolet to assess their power in determining the age of the stellar population in galaxies. We focus in particular on features that can differentiate between an old UV-bright population, contributing to the UV upturn, and a young population due to recent star formation. We use a system of 8 indices between 2200 - 3200A, tracing several chemical elements including Mg and Fe. We apply these models to a large sample of z ∼ 0.6 massive galaxies from the Sloan Digital Sky Survey (SDSS) - III / Baryon Oscillation Spectroscopic Survey (BOSS) to derive the ages of the UV-bright populations. We find a subset of indices to be non-degenerate between old and young UV ages allowing us to find evidence for old stars contributing to the UV, rather than new star formation. We find up to 84% of our working sample (274,661 galaxies) to contain a contribution from old UV-bright stars. Those found to have higher contributing mass fractions being on average more massive and redder then those with lower mass fractions.

Original languageEnglish
Pages (from-to)190-192
Number of pages3
JournalProceedings of the International Astronomical Union
Issue numberA29B
Publication statusPublished - 27 Oct 2016
EventXXIXth IAU General Assembly - Honolulu, United States
Duration: 3 Aug 201514 Aug 2015


  • galaxies: evolution - galaxies: stellar content - ultraviolet: galaxies


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