SIMBAD references

Aims. We seek is to identify old and massive galaxies at 0.5<z<2.1 on the basis of the magnesium index Mg_UV and then study their physical properties.
Methods. We computed the Mg_UV index based on the best spectral fitting template of ∼3700 galaxies using data from the VLT VIMOS Deep Survey (VVDS) and VIMOS Ultra Deep Survey (VUDS) galaxy redshift surveys. Based on galaxies with the largest signal to noise and the best fit spectra we selected 103 objects with the highest spectral Mg_UV signature. We performed an independent fit of the photometric data of these galaxies and computed their stellar masses, star formation rates, extinction by dust and age, and we related these quantities to the Mg_UV index.
Results. We find that the Mg_UV index is a suitable tracer of early-type galaxies at an advanced stage of evolution. Selecting galaxies with the highest Mg_UV index allows us to choose the most massive, passive, and oldest galaxies at any epoch. The formation epoch t_f computed from the fitted age as a function of the total mass in stars supports the downsizing formation paradigm in which galaxies with the highest mass formed most of their stars at an earlier epoch.