Recent studies have found a significant evolution and scatter in the relationship between the UV spectral slope (β UV ) and the infrared excess (IRX; L IR /L UV ) at z>4, suggesting different dust properties of these galaxies. The total farinfrared (FIR) luminosity is key for this analysis, but it is poorly constrained in normal (main-sequence) star-forming z>5 galaxies, where often only one single FIR point is available. To better inform estimates of the FIR luminosity, we construct a sample of local galaxies and three low-redshift analogues of z>5 systems. The trends in this sample suggest that normal high-redshift galaxies have a warmer infrared (IR) spectral energy distribution (SED) compared to average z<4 galaxies that are used as priors in these studies. The blueshifted peak and mid-IR excess emission could be explained by a combination of a larger fraction of metal-poor interstellar medium being optically thin to ultraviolet (UV) light and a stronger UV radiation field due to high star formation densities. Assuming a maximally warm IR SED suggests a 0.6 dex increase in total FIR luminosities, which removes some tension between the dust attenuation models and observations of the IRX−βrelation at z>5. Despite this, some galaxies still fall below the minimum IRX −βrelation derived with standard dust cloud models. We propose that radiation pressure in these highly star-forming galaxies causes a spatial offset between dust clouds and young star-forming regions within the lifetime of O/B stars. These offsets change the radiation balance and create viewing-angle effects that can change UV colors at fixed IRX. We provide a modified model that can explain the location of these galaxies on the IRX−βdiagram.

We examine the rest-frame ultraviolet (UV) properties of 10 [C II]λ158 μm-detected galaxies at z∼5.5 in COSMOS using new Hubble Space Telescope/Wide Field Camera 3 near-infrared imaging. Together with preexisting 158 μm continuum and [C II]line measurements by the Atacama Large Millimeter/submillimeter Array, we study their dust attenuation properties on the IRX-βdiagram, which connects the total dust emissionto the line-of-sight dust column (∝ β). We find systematically bluer UV continuum spectral slopes (β) compared to previous low-resolution ground-based measurements, which relieves some of the tension between models of dust attenuation and observations at high redshifts. While most of the galaxies are consistent with local starburst or Small Magellanic Cloud-like dust properties, we find galaxies with low IRX values and a large range in β that cannot be explained by models of a uniform dust distribution well mixed with stars. A stacking analysis of Keck/DEIMOS optical spectra indicates that these galaxies are metal-poor with young stellar populations that could significantly alter their spatial dust distribution.

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.

A decade of study has established that the molecular gas properties of star-forming galaxies follow coherent scaling relations out to z∼3, suggesting remarkable regularity of the interplay between molecular gas, star formation, and stellar growth. Passive galaxies, however, are expected to be gas-poor and therefore faint, and thus little is known about molecular gas in passive galaxies beyond the local universe. Here we present deep Atacama Large Millimeter/submillimeter Array observations of CO(2-1) emission in eight massive (M star ∼ 10 11 M e ) galaxies at z∼0.7 selected to lie a factor of 3-10 below the star-forming sequence at this redshift, drawn from the Large Early Galaxy Astrophysics Census survey. We significantly detect half the sample, finding molecular gas fractions 0.1. We show that the molecular and stellar rotational axes are broadly consistent, arguing that the molecular gas was not accreted after the galaxies became quiescent. We find that scaling relations extrapolated from the star-forming population overpredict both the gas fraction and gas depletion time for passive objects, suggesting the existence of either a break or large increase in scatter in these relations at low specific star formation rate. Finally, we show that the gas fractions of the passive galaxies we have observed at intermediate redshifts are naturally consistent with evolution into local, massive early-type galaxies by continued low-level star formation, with no need for further gas accretion or dynamical stabilization of the gas reservoirs in the intervening 6 billion years.

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.

We use reconstructed star-formation histories (SFHs) of quiescent galaxies at z = 0.6 − 1 in the LEGA-C survey to identify secondary star-formation episodes that, after an initial period of quiescence, moved the galaxies back to the star-forming main sequence (blue cloud). 16 ± 3% of the z ∼ 0.8 quiescent population has experienced such rejuvenation events in the redshift range 0.7 < z < 1.5 after reaching quiescence at some earlier time. On average, these galaxies first became quiescent at z = 1.2, and those that rejuvenated, remained quiescent for ∼ 1Gyr before their secondary SF episode which lasted ∼ 0.7Gyr. The stellar mass attributed to rejuvenation is on average 10% of the galaxy stellar mass, with rare instances of an increase of more than a factor 2. Overall, rejuvenation events only contribute ∼ 2% of the total stellar mass in z ∼ 0.8 quiescent galaxies and we conclude that rejuvenation is not an important evolutionary channel when considering the growth of the red sequence. However, our results complicate the interpretation of galaxy demographics in color space: the galaxies with rejuvenation events tend to lie in the so-called 'green valley', yet their progenitors were quiescent at z ∼ 2.