We analyze stellar age indicators (D n 4000 and EW(Hδ)) and sizes of 467 quiescent galaxies with M * ≥ 10 10 M at z ∼ 0.7 drawn from DR2 of the LEGA-C survey. Interpreting index variations in terms of equivalent single stellar population age, we find that the median stellar population is younger for larger galaxies at fixed stellar mass. The effect is significant, yet small; the ages of the larger and the smaller subsets differ by only < 500 Myr, much less than the age variation among individual galaxies (∼ 1.5 Gyr). At the same time, post-starburst galaxies -those experienced recent and rapid quenching events -are much smaller than expected based on the global correlation between age and size of normal quiescent galaxies. These co-existing trends unify seemingly contradictory results in the literature; the complex correlations between size and age indicators revealed by our large sample of galaxies with high-quality spectra suggest that there are multiple evolutionary pathways to quiescence. Regardless of the specific physical mechanisms responsible for the cessation of star formation in massive galaxies, the large scatter in D n 4000 and EW(Hδ) immediately implies that galaxies follow a large variety in evolutionary pathways. On the one hand, we see evidence for a process that slowly shuts off star-formation and transforms star-forming galaxies to quiescent galaxies without necessarily changing their structures. On the other hand, there is likely a mechanism that rapidly quenches galaxies, an event that coincides with dramatic structural changes, producing post-starburst galaxies that can be smaller than their progenitors.

We present the second data release of the Large Early Galaxy Astrophysics Census (LEGA-C), an ESO 130−night public spectroscopic survey conducted with VIMOS on the Very Large Telescope. We release 1988 spectra with typical continuum S/N 20Å −1 of galaxies at 0.6 z 1.0, each observed for ∼ 20 hours and fully reduced with a custom-built pipeline. We also release a catalog with spectroscopic redshifts, emission line fluxes, Lick/IDS indices, and observed stellar and gas velocity dispersions that are spatially integrated quantities including both rotational motions and genuine dispersion. To illustrate the new parameter space in the intermediate redshift regime probed by LEGA-C we explore relationships between dynamical and stellar population properties. The star-forming galaxies typically have observed stellar velocity dispersions of ∼ 150 km s −1 and strong Hδ absorption (Hδ A ∼ 5Å), while passive galaxies have higher observed stellar velocity dispersions (∼ 200 km s −1 ) and weak Hδ absortion (Hδ A ∼ 0Å). Strong [OIII]5007/Hβ ratios tend to occur mostly for galaxies with weak Hδ A or galaxies with higher observed velocity dispersion. Beyond these broad trends, we find a large diversity of possible combinations of rest-frame colors, absorption line strengths and emission line detections, illustrating the utility of spectroscopic measurements to more accurately understand galaxy evolution. By making the spectra and value-added catalogs publicly available we encourage the community to take advantage of this very substantial investment in telescope time provided by ESO.

The Large Early Galaxy Census (LEGA-C a ) is a Public Spectroscopic Survey of ∼ 3200 K-band selected galaxies at redshifts z = 0.6 − 1.0 with stellar masses M * > 10 10 M , conducted with VIMOS on ESO's Very Large Telescope. The survey is embedded in the COSMOS field (R.A. = 10h00; Dec. = +2 deg). The 20-hour long integrations produce high-S/N continuum spectra that reveal ages, metallicities and velocity dispersions of the stellar populations. LEGA-C's unique combination of sample size and depth will enable us for the first time to map the stellar content at large look-back time, across galaxies of different types and star-formation activity. Observations started in December 2014 and are planned to be completed by mid 2018, with early data releases of the spectra and valueadded products. In this paper we present the science case, the observing strategy, an overview of the data reduction process and data products, and a first look at the relationship between galaxy structure and spectral properties, as it existed 7 Gyr ago.

We present stellar rotation curves and velocity dispersion profiles for 104 quiescent galaxies at z = 0.6 − 1 from the Large Early Galaxy Astrophysics Census (LEGA-C) spectroscopic survey. Rotation is typically probed across 10-20kpc, or to an average of 2.7R e . Combined with central stellar velocity dispersions (σ 0 ) this provides the first determination of the dynamical state of a sample selected by a lack of star formation activity at large lookback time. The most massive galaxies (M > 2 × 10 11 M ) generally show no or little rotation measured at 5kpc (|V 5 |/σ 0 < 0.2 in 8 of 10 cases), while ∼64% of less massive galaxies show significant rotation. This is reminiscent of local fast-and slow-rotating ellipticals and implies that low-and high-redshift quiescent galaxies have qualitatively similar dynamical structures. We compare |V 5 |/σ 0 distributions at z ∼ 0.8 and the present day by re-binning and smoothing the kinematic maps of 91 low-redshift quiescent galaxies from the CALIFA survey and find evidence for a decrease in rotational support since z ∼ 1. This result is especially strong when galaxies are compared at fixed velocity dispersion; if velocity dispersion does not evolve for individual galaxies then the rotational velocity at 5kpc was an average of 94 ± 22% higher in z ∼ 0.8 quiescent galaxies than today. Considering that the number of quiescent galaxies grows with time and that new additions to the population descend from rotationally-supported star-forming galaxies, our results imply that quiescent galaxies must lose angular momentum between z ∼ 1 and the present, presumably through dissipationless merging, and/or that the mechanism that transforms star-forming galaxies also reduces their rotational support.

We analyze the colors and sizes of 32 quiescent (UVJ-selected) galaxies with strong Balmer absorption (EW(Hδ) ≥ 4Å) at z ∼ 0.8 drawn from DR2 of the LEGA-C survey to test the hypothesis that these galaxies experienced compact, central starbursts before quenching. These recently quenched galaxies, usually referred to as post-starburst galaxies, span a wide range of colors and we find a clear correlation between color and half-light radius, such that bluer galaxies are smaller. We build simple toy models to explain this correlation: a normal star-forming disk plus a central, compact starburst component. Bursts with exponential decay timescale of ∼ 100 Myr that produce ∼ 10% to more than 100% of the pre-existing masses can reproduce the observed correlation. More significant bursts also produce bluer and smaller descendants. Our findings imply that when galaxies shut down star formation rapidly, they generally had experienced compact, starburst events and that the large, observed spread in sizes and colors mostly reflects a variety of burst strengths. Recently quenched galaxies should have younger stellar ages in the centers; multi-wavelength data with high spatial resolution are required to reveal the age gradient. Highly dissipative processes should be responsible for this type of formation history. While determining the mechanisms for individual galaxies is challenging, some recently quenched galaxies show signs of gravitational interactions, suggesting that mergers are likely an important mechanism in triggering the rapid shut-down of star-formation activities at z ∼ 0.8.