The VANDELS survey: the star-formation histories of massive quiescent galaxies at 1.0 < z < 1.3

Abstract

We present a Bayesian full-spectral-fitting analysis of 75 massive ($M_{\ast }>10^{10.3}{M}_{\odot }$) UVJ-selected galaxies at redshifts of $1.0<z<1.3$, combining extremely deep rest-frame ultraviolet spectroscopy from VANDELS with multi-wavelength photometry. By the use of a sophisticated physical plus systematic uncertainties model, constructed within the Bagpipes code, we place strong constraints on the star-formation histories (SFHs) of individual objects. We firstly constrain the stellar mass vs stellar age relationship, finding a steep trend towards earlier average formation with increasing stellar mass of $1.48_{-0.39}^{+0.34}$ Gyr per decade in mass, although this shows signs of flattening at $M_{\ast }>10^{11}{M}_{\odot }$. We show that this is consistent with other spectroscopic studies from $0<z<2$. This relationship places strong constraints on the AGN-feedback models used in cosmological simulations. We demonstrate that, although the relationships predicted by Simba and IllustrisTNG agree well with observations at $z=0.1$, they are too shallow at $z=1$, predicting an evolution of $<0.5$ Gyr per decade in mass. Secondly, we consider the connections between green-valley, post-starburst and quiescent galaxies, using our inferred SFH shapes and the distributions of galaxy physical properties on the UVJ diagram. The majority of our lowest-mass galaxies ($M_{\ast }\sim 10^{10.5}{M}_{\odot }$) are consistent with formation in recent ($z<2$), intense starburst events, with timescales of $\lesssim 500$ Myr. A second class of objects experience extended star-formation epochs before rapidly quenching, passing through both green-valley and post-starburst phases. The most massive galaxies in our sample are extreme systems: already old by $z=1$, they formed at $z\sim 5$ and quenched by $z=3$. However, we find evidence for their continued evolution through both AGN and rejuvenated star-formation activity.

25 pages, 13 figures, MNRAS accepted