The elemental abundance of quiescent galaxies in the LEGA-C survey: The (non-)evolution of [α/Fe] from z = 0.75 to z = 0

Abstract

We measure the [?/Fe] abundances for 183 quiescent galaxies at z = 0.60-0.75 with stellar masses ranging 10.4 ? log10(M?/MâŠ) ? 11.6 selected from the Large Early Galaxy Astrophysics Census survey. We estimate [?/Fe] from the ratio of the spectral indices Mgb (? ?5177 Å) and Fe4383, compared to predictions of simple stellar population models. We find that 91 per cent of quiescents in our sample have supersolar [?/Fe], with an average value of [?/Fe] = +0.24 ± 0.01. We find no significant correlation between [?/Fe] and stellar metallicity, mass, velocity dispersion, and average formation time. Galaxies that formed the bulk of their stellar mass on time-scales shorter than 1 Gyr follow the same [?/Fe] distribution as those which formed on longer time-scales. In comparison to local early-Type galaxies and to stacked spectra of quiescent galaxies at z = 0.38 and z = 0.07, we find that the average [?/Fe] has not changed between z = 0.75 and the present time. Our work shows that the vast majority of massive quiescent galaxies at z ?0.7 are ?-enhanced, and that no detectable evolution of the average [?/Fe] has taken place over the last ?6.5 Gyr.