2019/03/31 by A. C. Carnall, R. J. McLure, J. S. Dunlop +19 · 1 citation
Physics and Astronomy · #astro-ph.GA #astro-ph.IM
paper · pdf · doi:10.1093/mnras/stz2544
25 pages, 13 figures, MNRAS accepted
arxiv created 2019/10/24 · arxiv updated 2019/10/25
We present a Bayesian full-spectral-fitting analysis of 75 massive (M_* > 1010.3 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+0.34-0.39 Gyr per decade in mass, although this shows signs of flattening at M_* > 1011 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_* ∼ 1010.5 M_\odot) are consistent with formation in recent (z<2), intense starburst events, with timescales of \lesssim500 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∼5 and quenched by z=3. However, we find evidence for their continued evolution through both AGN and rejuvenated star-formation activity.