The connection between stellar mass, age and quenching timescale in massive quiescent galaxies at z ≃ 1

We present a spectro-photometric study of a mass-complete sample of quiescent galaxies at 1.0 < z < 1.3 with log10(M⋆/M⊙)≥10.3 drawn from the VANDELS survey, exploring the relationship between stellar mass, age and star-formation history. Within our sample of 114 galaxies, we derive a stellar-mass vs stellar-age relation with a slope of 1.20+0.28−0.27 Gyr per decade in stellar mass. When combined with recent literature results, we find evidence that the slope of this relation remains consistent over the redshift interval 0 < z < 4. The galaxies within the VANDELS quiescent display a wide range of star-formation histories, with a mean star-formation timescale of 1.5 ± 0.1 Gyr and a mean quenching timescale of 1.4 ± 0.1 Gyr. We also find a large scatter in the quenching timescales of the VANDELS quiescent galaxies, in agreement with previous evidence that galaxies at z ∼ 1 cease star formation via multiple mechanisms. We then focus on the oldest galaxies in our sample, finding that the number density of galaxies that quenched before z = 3 with stellar masses log10(M⋆/M⊙)≥10.6 is 1.12+1.47−0.72×10−5 Mpc−3⁠. Although uncertain, this estimate is in good agreement with the latest observational results at 3 < z < 4, tentatively suggesting that neither rejuvenation nor merger events are playing a major role in the evolution of the oldest massive quiescent galaxies within the redshift interval 1 < z < 3.