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 ($M_* \gt 10^{10.3} \, \mathrm{M_\odot }$) UVJ-selected galaxies at redshifts of 1.0 < z < 1.3, combining extremely deep rest-frame ultraviolet spectroscopy from VANDELS with multiwavelength 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 first constrain the stellar mass versus stellar age relationship, finding a steep trend towards earlier average formation time with increasing stellar mass (downsizing) of $1.48^{+0.34}_{-0.39}$ Gyr per decade in mass, although this shows signs of flattening at $M_* \gt 10^{11} \, \mathrm{M_\odot }$. 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 ($M_* \sim 10^{10.5} \, \mathrm{M_\odot }$) are consistent with formation in recent (z < 2), intense starburst events, with time-scales of ≲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 ∼ 5 and quenched by z = 3. However, we find evidence for their continued evolution through both AGN and rejuvenated star-formation activity.

The star formation histories of z ∼ 1 post-starburst galaxies

“…The double power-law model used in the initial fits has been shown to work well for quiescent galaxies (Carnall et al 2019a). However, it only allows a single rise and fall in star formation over time.…”

The GOGREEN survey: post-infall environmental quenching fails to predict the observed age difference between quiescent field and cluster galaxies at z > 1

“…While recent spectroscopic surveys have collected larger samples of quiescent galaxies at higher redshifts (e.g. Pacifici et al 2016;Thomas et al 2017;Carnall et al 2019a;Estrada-Carpenter et al 2019), there has not yet been a systematic study of the SFHs with environment. We can significantly improve our understanding of the differences in SFHs of galaxies related to their environment with the Gemini Observations of Rich Early ENvironments survey (GOGREEN 1 ; Balogh et al 2017, Balogh et al 2020in prep.).…”

“…In fitting the spectroscopy and photometry together, we need to account for uncertainties in the spectral response calibration, and for the overall flux calibration due to slit losses. Several authors have demonstrated the challenge of simultaneously fitting spectral and photometric data, especially when the spectral continuum is not well characterised (Panter et al 2007;van der Wel et al 2016;Belli et al 2019;Carnall et al 2019a;Johnson et al 2019). As described in Section 2.2, the spectra were not absolute flux calibrated.…”

“…tometry for more than 600 galaxies at 0.6<z<1 from LEGA-C (van der Wel et al 2016;Straatman et al 2018) to show that galaxies with higher stellar velocity dispersions formed both earlier and faster, and that the majority of quiescent galaxies evolve passively since their main star forming epoch. Carnall et al (2019a) similarly use the VANDELS survey (McLure et al 2018;Pentericci et al 2018) to determine the SFHs for 75 massive quiescent galaxies at 1<z<1.3, finding a trend between the average formation times of galaxies and their stellar mass of 1.48 +0.34 −0.39 Gyr per dex for M * <10 11 M . The mass-dependent evolution in the GOGREEN quiescent galaxies is apparent in Figure 5, where we find the more massive galaxies to have sSFRs which are higher at earlier times, and decline at earlier times, than the lower mass galaxies, at fixed environment.…”

“…The ∼1 Gyr offset in ages could be a result of differences in fitting procedure, where Leja et al (2019b) report that Prospector -α 12 predicts older ages and higher stellar masses than standard parametric modelling. Carnall et al (2019a) use a double-power-law form for their SFHs, however, which is more flexible than fiducial declining-exponential models, so the ages should be more similar than those reported by Leja et al (2019b). Along the same lines, Forrest et al (2020b;submitted) reconstruct the SFHs of ultra massive (>10 11 M ) galaxies at 3<z<4 and find that the bulk of star formation occurred between 4<z<6 ( 0.5 Gyr later than the median mass-weighted ages we measure), and the galaxies quenched several hundred Myr later, in some cases as early as z∼4.…”