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This is a correction for 2022 ApJ 926 89DOI 10.3847/1538-4357/ac404a

The Large Early Galaxy Astrophysics Census (LEGA-C) survey is the final Public Spectroscopic Survey to be completed with the now-retired VIsible Multi-Object Spectrograph (VIMOS) instrument at ESO���s Very Large Telescope (VLT). Its aim is to characterise with high precision and for a very large sample the stellar population and kinematic properties of galaxies at redshifts 0.6 < z < 1, providing a first assessment of the star formation histories, the absolute mass scale, and the stellar kinematic structure of galaxies at large lookback times (7 gigayears ago). This article coincides with the third and final data release but mostly focuses on the large variety of scientific results achieved so far., Published in The Messenger vol. 185, pp. 13-17, December 2021.

LEGA-C is revealing, for the first time, the star-formation history and stellar kinematic properties for the general galaxy population at large lookback time (z=0.6-1). I will present the third and final data release, summarize results so far, and give a preview of what we can expect to see over the next few days in this meeting and over the coming months: how high-quality spectroscopy facilities the transition from a qualitative to a quantitative description of the stellar dynamical and stellar population evolution of galaxies.

We present COSMOS-Drift And SHift (DASH), a Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging survey of the COSMOS field in the H 160 filter. The survey comprises 456 individual WFC3 pointings corresponding to an area of 0.49 deg2 (0.66 deg2 when including archival data) and reaches a 5σ point- source limit of H 160 = 25.1 (0.″3 aperture). COSMOS-DASH is the widest HST/WFC3 imaging survey in the H 160 filter, tripling the extragalactic survey area in the near-infrared at HST resolution. We make the reduced H 160 mosaic available to the community. We use this data set to measure the sizes of 169 galaxies with {log}({M}\star /{M}ȯ )> 11.3 at 1.5 < z < 3.0 and augment this sample with 749 galaxies at 0.1 < z < 1.5 using archival ACS imaging. We find that the median size of galaxies in this mass range changes with redshift as < {r}eff}> ={(13.4+/- 0.5)× (1+z)}(-0.95+/- 0.05) kpc. Separating the galaxies into star-forming and quiescent galaxies using their rest-frame U − V and V − J colors, we find no statistical difference between the median sizes of the most massive star-forming and quiescent galaxies at < z> =2.5: they are 4.9 ± 0.9 kpc and 4.3 ± 0.3 kpc, respectively. However, we do find a significant difference in the Sèrsic index between the two samples, such that massive quiescent galaxies have higher central densities than star-forming galaxies. We extend the size−mass analysis to lower masses by combining it with the 3D-HST/CANDELS sample of van der Wel et al. and derive empirical relations between size, mass, and redshift. Fitting a relation of the form {r}eff}=A× {m}\star α , with {m}\star ={M}\star /5× {10}10 {M}ȯ and r eff in kpc, we find log A = −0.25 log(1 + z) + 0.80 and α = −0.13 log(1 + z) + 0.27. We also provide relations for the subsamples of star-forming and quiescent galaxies. Our results confirm previous studies that were based on smaller samples or ground-based imaging.

Drawing from the LEGA-C data set, we present the spectroscopic view of the stellar population across a large volume- and mass-selected sample of galaxies at large look-back time. We measure the 4000 Å break (D n 4000) and Balmer absorption line strengths (probed by Hδ) from 1019 high-quality spectra of z = 0.6-1.0 galaxies with M * = 2 × 1010 M ☉ to 3 × 1011 M ☉. Our analysis serves as a first illustration of the power of high-resolution, high signal-to-noise ratio continuum spectroscopy at intermediate redshifts as a qualitatively new tool to constrain galaxy formation models. The observed D n 4000-EW(Hδ) distribution of our sample overlaps with the distribution traced by present-day galaxies, but z ̃ 0.8 galaxies populate that locus in a fundamentally different manner. While old galaxies dominate the present-day population at all stellar masses >2 × 1010 M ☉, we see a bimodal D n 4000-EW(Hδ) distribution at z ̃ 0.8, implying a bimodal light-weighted age distribution. The light-weighted age depends strongly on stellar mass, with the most massive galaxies >1 × 1011 M ☉ being almost all older than 2 Gyr. At the same time, we estimate that galaxies in this high-mass range are only ̃3 Gyr younger than their z ̃ 0.1 counterparts, at odds with purely passive evolution given a difference in look-back time of >5 Gyr; younger galaxies must grow to >1011 M ☉ in the meantime, or small amounts of young stars must keep the light-weighted ages young. Star-forming galaxies at z ̃ 0.8 have stronger Hδ absorption than present-day galaxies with the same D n 4000, implying larger short-term variations in star formation activity.

The LEGA-C (Large Early Galaxy Census) survey is made possible by the refurbishment of the Very Large Telescope VIsible and Multi Object Spectrograph (VIMOS) instrument and the implementation by ESO of a new generation of large spectroscopic surveys. The goal is to obtain high-quality continuum spectra of thousands of galaxies with redshifts up to z = 1, with which key physical parameters that were previously inaccessible can be measured. These include star formation histories and dynamical masses, which greatly improve our insight into how galaxies form and evolve. This article coincides with the first public data release of fully reduced and calibrated spectra.

We explore how the presence of detectable molecular gas depends on the inferred star formation histories (SFHs) in eight massive, quiescent galaxies at z ∼ 0.7. Half of the sample have clear detections of molecular gas, traced by CO(2–1). We find that the molecular gas content is unrelated to the rate of star formation decline prior to the most recent 1 Gyr, suggesting that the gas reservoirs are not left over from their primary star formation epoch. However, the recent SFHs of CO-detected galaxies demonstrate evidence for secondary bursts of star formation in their last Gyr. The fraction of stellar mass formed in these secondary bursts ranges from f burst ≈ 0.3%–6% and ended between t end-burst ≈ 0–330 Myr ago. The CO-detected galaxies form a higher fraction of mass in the last Gyr ( f M 1 Gyr = 2.6 % ± 1.8 % ) compared to the CO-undetected galaxies ( f M 1 Gyr = 0.2 % ± 0.1 % ). The galaxies with gas reservoirs have enhanced late-time star formation, highlighting this as a contributing factor to the observed heterogeneity in the gas reservoirs in high-redshift quiescent galaxies. We find that the amount of gas and star formation driven by these secondary bursts are inconsistent with that expected from dry minor mergers, and instead are likely driven by recently accreted gas, i.e., gas-rich minor mergers. This conclusion would not have been made based on SFRUV+IR measurements alone, highlighting the power of detailed SFH modeling in the interpretation of gas reservoirs. Larger samples are needed to understand the frequency of low-level rejuvenation among quiescent galaxies at intermediate redshifts, and to what extent this drives the diversity of molecular gas reservoirs.

The first few 100 Myr at z > 10 mark the last major uncharted epoch in the history of the universe, where only a single galaxy (GN-z11 at z ≈ 11) is currently spectroscopically confirmed. Here we present a search for luminous z > 10 galaxies with JWST/NIRCam photometry spanning ≈1–5 μm and covering 49 arcmin2 from the public JWST Early Release Science programs (CEERS and GLASS). Our most secure candidates are two MUV ≈ −21 systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt ≳1.8 mag breaks in their spectral energy distributions (SEDs), consistent with complete absorption of flux bluewards of Lyα that is redshifted to =+z12.40.3 0.1and=+z10.40.5 0.4. Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at >5σ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up ∼109 solar masses in stars over the ≲300–400 Myr after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of r50 ≈ 0.7 kpc. These sources, if confirmed, join GN-z11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area >10× larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep JWST observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated., R.P.N. acknowledges funding from JWST programs GO-1933 and GO-2279. Support for this work was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51515.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. We acknowledge support from: the Swiss National Science Foundation through project grant 200020_207349 (P.A.O., A.W.). The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant No. 140. R.J.B. and M.S. acknowledge support from NWO grant TOP1.16.057

Galaxies in the local Universe fall into two main categories of spirals and ellipticals. In this Thesis, we explore the structural evolution of galaxies into this bimodal distribution. To do so, we study galaxies in the context of the Fundamental Plane, the tight scaling relation between galaxy size, kinematics and luminosity, which connects the structural and stellar population properties of galaxies. This work is built on a combination of observational data and theoretical models. Large spectroscopic surveys are used to construct a representative sample of massive quiescent and star-forming galaxies across 8 Gyr of cosmic time. We hence show that there is strong variation and evolution in the mass-to-light ratios of galaxies, due to evolution in the stellar populations. However, surprisingly, all galaxies lie on a single mass Fundamental Plane, which does not evolve with time. Cosmological simulations are used to assess the structural properties that may underlie the observed mass Fundamental Plane. Based on the simulations, we propose that this relation may originate from a systematic variation in the central dark matter content within galaxies as a function of their size and mass.

With just a month of data, JWST is already transforming our view of the universe, revealing and resolving starlight in unprecedented populations of galaxies. Although “HST-dark” galaxies have previously been detected at long wavelengths, these observations generally suffer from a lack of spatial resolution, which limits our ability to characterize their sizes and morphologies. Here we report on a first view of starlight from a subset of the HST-dark population that is bright with JWST/NIRCam (4.4 μm < 24.5 mag) and very faint or even invisible with HST (μm). In this Letter we focus on a dramatic and unanticipated population of physically extended galaxies (≳0.″25). These 12 galaxies have photometric redshifts 2 < z < 6, high stellar masses M ⋆ ≳ 1010 M ⊙, and significant dust-attenuated star formation. Surprisingly, the galaxies have elongated projected axis ratios at 4.4 μm, suggesting that the population is disk dominated or prolate and we hence refer to them as ultrared flattened objects. Most of the galaxies appear red at all radii, suggesting significant dust attenuation throughout. With R e (F444W) ∼ 1–2 kpc, the galaxies are similar in size to compact massive galaxies at z ∼ 2 and the cores of massive galaxies and S0s at z ∼ 0. The stellar masses, sizes, and morphologies of the sample suggest that some could be progenitors of lenticular or fast-rotating galaxies in the local universe. The existence of this population suggests that our previous censuses of the universe may have missed massive, dusty edge-on disks, in addition to dust-obscured starbursts.