Unveiling the afterlife of galaxies with ultraviolet data

Abstract

Abstract. Recent works have shown that early-type galaxies (ETGs) are much more complex than early studies suggested. We present early results from a combined analysis of optical spectra and ultraviolet photometry for a sample of 3453 red sequence galaxies in at z < 0.1 that are classified as elliptical by Galaxy Zoo. By measuring the Gini index of the star-formation histories derived by starlight, we investigate the complexity of the mixture of stellar populations required to describe ETGs in our sample. When fitting only optical spectra, starlight assigns more or less the same mixture of stellar populations to all ETGs, while the addition of UV data unveils a bimodallity in the star-formation histories of these galaxies. We find evidence for stellar populations younger than 1 Gyr in 17 per cent of our sample, indicating that some galaxies do not stay permanently quenched after reaching the red sequence.