Observations have revealed massive (log M∗/Mo ≳ 11) galaxies that were already dead when the universe was only ∼2 Gyr. Given the short time before these galaxies were quenched, their past histories and quenching mechanism(s) are of particular interest. In this paper, we study star formation histories (SFHs) of 24 massive galaxies at 1.6 < z < 2.5. A deep slitless spectroscopy and imaging data set collected from multiple Hubble Space Telescope surveys allows robust determination of their spectral energy distributions and SFHs with no functional assumption on their forms. We find that most of our massive galaxies had formed >50% of their extant masses by ∼1.5 Gyr before the time of observed redshifts, with a trend where more massive galaxies form earlier. Their stellar-phase metallicities are already compatible with those of local early-type galaxies, with a median value of log Z∗/Zo = 0.25 and scatter of ∼0.15 dex. In combination with the reconstructed SFHs, we reveal their rapid metallicity evolution from z ∼ 5.5 to ∼2.2 at a rate of ∼0.2 dex Gyr-1 in Z∗/Zo. Interestingly, the inferred stellar-phase metallicities are, when compared at half-mass time, ∼0.25 dex higher than observed gas-phase metallicities of star-forming galaxies. While systematic uncertainties remain, this may imply that these quenched galaxies have continued low-level star formation, rather than abruptly terminating their star formation activity, and kept enhancing their metallicity until recently.

Local massive early-type galaxies are believed to have completed most of their star formation ∼10 Gyr ago and evolved without having substantial star formation since that time. If so, their progenitors should have roughly solar stellar metallicities (Z∗), comparable to their values today. We report the discovery of two lensed massive (), z ∼ 2.2 dead galaxies that appear markedly metal deficient given this scenario. Using 17-band HST+Ks+Spitzer photometry and deep Hubble Space Telescope (HST) grism spectra from the Grism Lens Amplified Survey from Space (GLASS) and supernova (SN) Refsdal follow-up campaigns covering features near λrest ∼ 4000A, we find these systems to be dominated by A-type stars with and -0.49 ± 0.03 (30%-40% solar) under standard assumptions. The second system's lower metallicity is robust to isochrone changes, though this choice can drive the first system's from to 0.1. If these two galaxies are representative of larger samples, this finding suggests that evolutionary paths other than dry minor merging are required for these massive galaxies. Future analyses with direct metallicity measurements - e.g., by the James Webb Space Telescope - will provide critical insight into the nature of such phenomena.

The primary goals of the STRong lensing Insights into the Dark Energy Survey (STRIDES) collaboration are to measure the dark energy equation of state parameter and the free streaming length of dark matter. To this aim, STRIDES is discovering strongly lensed quasars in the imaging data of the Dark Energy Survey and following them up to measure time delays, high resolution imaging, and spectroscopy sufficient to construct accurate lens models. In this paper, we first present forecasts for STRIDES. Then, we describe the STRIDES classification scheme, and give an overview of the Fall 2016 follow-up campaign. We continue by detailing the results of two selection methods, the outlier selection technique and a morphological algorithm, and presenting lens models of a system that could possibly be a lensed quasar in an unusual configuration. We conclude with the summary statistics of the Fall 2016 campaign. Including searches presented in companion papers (Anguita et al.; Ostrovski et al.), STRIDES followed up 117 targets identifying 7 new strongly lensed systems, and 7 nearly identical quasars, which could be confirmed as lenses by the detection of the lens galaxy. 76 candidates were rejected and 27 remain otherwise inconclusive, for a success rate in the range of 6-35 per cent. This rate is comparable to that of previous searches like SDSS Quasar Lens Search even though the parent data set of STRIDES is purely photometric and our selection of candidates cannot rely on spectroscopic information.