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Galaxy evolution is driven by a variety of physical processes that are predicted to proceed at different rates for different dark matter haloes and environments across cosmic times. A record of this evolution is preserved in galaxy stellar populations, which we can access using absorption-line spectroscopy. Here we explore the large LEGA-C survey (DR3) to investigate the role of the environment and stellar mass on stellar populations at z similar to 0.6-1 in the COSMOS field. Leveraging the statistical power and depth of LEGA-C, we reveal significant gradients in D( n )4000 and H delta equivalent widths (EWs) distributions over the stellar mass versus environment 2D spaces for the massive galaxy population (M > 10(10) M (circle dot)) at z similar to 0.6-1.0. D( n )4000 and H delta EWs primarily depend on stellar mass, but they also depend on environment at fixed stellar mass. By splitting the sample into centrals and satellites, and in terms of star-forming galaxies and quiescent galaxies, we reveal that the significant environmental trends of D( n )4000 and H delta EW, when controlling for stellar mass, are driven by quiescent galaxies. Regardless of being centrals or satellites, star-forming galaxies reveal D( n )4000 and H delta EWs, which depend strongly on their stellar mass and are completely independent of the environment at 0.6 < z < 1.0. The environmental trends seen for satellite galaxies are fully driven by the trends that hold only for quiescent galaxies, combined with the strong environmental dependency of the quiescent fraction at fixed stellar mass. Our results are consistent with recent predictions from simulations that point toward massive galaxies forming first in overdensities or the most compact dark matter haloes., The Astrophysical Journal, 926 (2), ISSN:0004-637X, ISSN:2041-8213

Post-starburst (PSB) galaxies are quiescent galaxies whose star-formation rates had dropped rapidly in the recent past thus good proxies to study quenching. They are traditionally selected by spectra. Therefore, comparing samples across redshifts are complicated by different spectroscopic apertures. I start from PSB galaxies in the MaNGA IFU survey at z=0, using the spectra integrated over the entire IFU. The large aperture mitigates the severe aperture bias with fiber spectra on low-z galaxies. I show that most of the PSB galaxies appear to have a fading compact star-formation event in the central 1 kpc. I then present the sample at z~1 identified by the LEGA-C survey. PSB galaxies at z~1 show overall stronger Balmer absorption at the center. Smaller ones are also bluer. Central compact star formation before quenching can explain these features of PSB galaxies at z=1. I will discuss the mechanisms, possible improvements, and new opportunities.

The LEGA-C survey is a large deep spectroscopy survey of the Universe at a lookback time of 7 Gyr. We use partially-resolved spatial information to present the first study of spatially-resolved stellar population properties on a statistically significant sample in the distant Universe. We show that i) post-starburst galaxies at z=1 show inverse age gradients, consistent with the effect of a central starburst and ii) star-forming galaxies show strong metallicity gradients, consistent with what is observed in the local Universe.

We present the third and final data release of the Large Early Galaxy Astrophysics Census (LEGA-C), an ESO/VLT public spectroscopic survey targeting $0.6 < z < 1.0$, Ks-selected galaxies. The data release contains 3528 spectra with measured stellar velocity dispersions and stellar population properties, a 25-fold increase in sample size compared to previous work. This $K_s$-selected sample probes the galaxy population down to $\sim0.3 L^*$, for all colors and morphological types. Along with the spectra we publish a value-added catalog with stellar and ionized gas velocity dispersions, stellar absorption line indices, emission line fluxes and equivalent widths, complemented with structural parameters measured from HST/ACS imaging. With its combination of high precision and large sample size, LEGA-C provides a new benchmark for galaxy evolution studies., Accepted for publication in ApJS. Data available at http://archive.eso.org/cms/eso-archive-news/Third-and-final-release-of-the-Large-Early-Galaxy-Census-LEGA-C-Spectroscopic-Public-Survey-published.html or https://users.ugent.be/\string~avdrwel/research.html\#legac

Galaxy evolution is driven by a variety of physical processes which are predicted to proceed at different rates for different dark matter haloes and environments across cosmic times. A record of this evolution is preserved in galaxy stellar populations, which we can access using absorption-line spectroscopy. Here we explore the large LEGA-C survey (DR3) to investigate the role of the environment and stellar mass on stellar populations at z~0.6-1.0 in the COSMOS field. Leveraging the statistical power and depth of LEGA-C, we reveal significant gradients in D4000 and H-delta equivalent widths (EWs) distributions over the stellar mass vs environment 2D spaces for the massive galaxy population (M>10^10 M$_{\odot}$) at z~0.6-1.0. D4000 and H-delta EWs primarily depend on stellar mass, but they also depend on environment at fixed stellar mass. By splitting the sample into centrals and satellites, and in terms of star-forming galaxies and quiescent galaxies, we reveal that the significant environmental trends of D4000 and H-delta EW when controlling for stellar mass are driven by quiescent galaxies. Regardless of being centrals or satellites, star-forming galaxies reveal D4000 and H-delta EWs which depend strongly on their stellar mass and are completely independent of the environment at 0.6, Comment: Accepted for publication in ApJ. 18 pages, 9 figures

Using deep rest-frame optical spectroscopy from the Large Early Galaxy Astrophysical Census (LEGA-C) survey, conducted using VIMOS on the ESO Very Large Telescope, we systematically search for low-ionization [OII] 3726,3729 emission in the spectra of a mass-complete sample of z~0.85 galaxies. Intriguingly, we find that 59 percent of UVJ-quiescent (i.e. non star-forming) galaxies in the sample have ionized gas, as traced by [OII] emission, detected above our completeness limit of 1.5 Angstroms. The median stacked spectrum of the lowest equivalent width quiescent galaxies also shows [OII] emission. The overall fraction of sources with [OII] above our equivalent width limit is comparable to what we find in the low-redshift Universe from GAMA and MASSIVE, except perhaps at the highest stellar masses (log Mstar/Msol > 11.5). However, stacked spectra for the individual low-equivalent width systems uniquely indicates ubiquitous [OII] emission in the higher-z LEGA-C sample, with typical [OII] luminosities per unit stellar mass that are a factor of 3 larger than the lower-z GAMA sample. Star formation in these otherwise quiescent galaxies could play a role in producing the [OII] emission at higher-z, although it is unlikely to provide the bulk of the ionizing photons. More work is required to fully quantify the contributions of evolved stellar populations or active galactic nuclei to the observed spectra., ApJ accepted: 16 pages, 11 figures

Recent zoom-in cosmological simulations have shown that stellar feedback can flatten the inner density profile of the dark matter halo in low-mass galaxies. A correlation between the stellar/gas velocity dispersion ($��_{star}$, $��_{gas}$) and the specific star formation rate (sSFR) is predicted as an observational test of the role of stellar feedback in re-shaping the dark matter density profile. In this work we test the validity of this prediction by studying a sample of star-forming galaxies at $0.6, 8 pages, 2 figures, 3 tables. Revised version. ApJL in press

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 ~= 20 /Angstrom 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 and strong Hdelta absorption (Hd_A ~ 5 Angstrom), while passive galaxies have higher observed stellar velocity dispersions ~200 km/s and weak Hdelta absortion (Hd_A ~ 0 Angstrom). Strong [O III]5007 / Hbeta ratios tend to occur mostly for galaxies with weak Hd_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., Comment: accepted for publication by ApJ; LEGA-C data-release http://www.mpia.de/home/legac/

Drawing from the LEGA-C dataset, we present the spectroscopic view of the stellar population across a large volume- and mass-selected sample of galaxies at large lookback time. We measure the 4000\AA\ break (D$_n$4000) and Balmer absorption line strengths (probed by H$\delta$) from 1019 high-quality spectra of $z=0.6 - 1.0$ galaxies with $M_\ast = 2 \times 10^{10} M_\odot - 3 \times 10^{11} M_\odot$. Our analysis serves as a first illustration of the power of high-resolution, high-S/N continuum spectroscopy at intermediate redshifts as a qualitatively new tool to constrain galaxy formation models. The observed D$_n$4000-EW(H$\delta$) distribution of our sample overlaps with the distribution traced by present-day galaxies, but $z\sim 0.8$ galaxies populate that locus in a fundamentally different manner. While old galaxies dominate the present-day population at all stellar masses $> 2\times10^{10} M_\odot$, we see a bimodal D$_n$4000-EW(H$\delta$) distribution at $z\sim0.8$, implying a bimodal light-weighted age distribution. The light-weighted age depends strongly on stellar mass, with the most massive galaxies $>1\times10^{11}M_\odot$ being almost all older than 2 Gyr. At the same time we estimate that galaxies in this high mass range are only $\sim3$ Gyr younger than their $z\sim0.1$ counterparts, at odd with pure passive evolution given a difference in lookback time of $>5$ Gyr; younger galaxies must grow to $>10^{11}M_\odot$ in the meantime, and/or small amounts of young stars must keep the light-weighted ages young. Star-forming galaxies at $z\sim0.8$ have stronger H$\delta$ absorption than present-day galaxies with the same D$_n$4000, implying larger short-term variations in star-formation activity., Comment: 17 pages, 9 figures, accepted by ApJ

Using high resolution spectra from the VLT LEGA-C program, we reconstruct the star formation histories (SFHs) of 607 galaxies at redshifts $z = 0.6-1.0$ and stellar masses $\gtrsim10^{10}$M$_{\odot}$ using a custom full spectrum fitting algorithm that incorporates the emcee and FSPS packages. We show that the mass-weighted age of a galaxy correlates strongly with stellar velocity dispersion ($��_*$) and ongoing star-formation (SF) activity, with the stellar content in higher-$��_*$ galaxies having formed earlier and faster. The SFHs of quiescent galaxies are generally consistent with passive evolution since their main SF epoch, but a minority show clear evidence of a rejuvenation event in their recent past. The mean age of stars in galaxies that are star-forming is generally significantly younger, with SF peaking after $z100$Myrs. This indicates that $z>2$ progenitors of $z\sim1$ star-forming galaxies are generally far less massive. Finally, despite considerable variance in the individual SFHs, we show that the current SF activity of massive galaxies ($>$L$_*$) at $z\sim1$ correlates with SF levels at least $3$Gyrs prior: SFHs retain `memory' on a large fraction of the Hubble time. Our results illustrate a novel approach to resolve the formation phase of galaxies, and in identifying their individual evolutionary paths, connects progenitors and descendants across cosmic time. This is uniquely enabled by the high-quality continuum spectroscopy provided by the LEGA-C survey., 18 pages, 9 figures, accepted by ApJ

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 ~= 20 /Angstrom 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 and strong Hdelta absorption (Hd_A ~ 5 Angstrom), while passive galaxies have higher observed stellar velocity dispersions ~200 km/s and weak Hdelta absortion (Hd_A ~ 0 Angstrom). Strong [O III]5007 / Hbeta ratios tend to occur mostly for galaxies with weak Hd_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., accepted for publication by ApJ; LEGA-C data-release http://www.mpia.de/home/legac/

In this study, we investigate 89 radio galaxies that are spectroscopically confirmed to be members of five large-scale structures (LSSs) in the redshift range of 0.65 ≤ z ≤ 0.96. Based on a two-stage classification scheme, the radio galaxies are classified into three sub-classes: active galactic nucleus (AGN), Hybrid, and star-forming galaxy (SFG). We study the properties of the three radio sub-classes and their global and local environmental preferences. We find AGN hosts are the most massive population and exhibit quiescence in their star formation activity. The SFG population has a comparable stellar mass to those hosting a radio AGN but are unequivocally powered by star formation. Hybrids, though selected as an intermediate population in our classification scheme, were found in almost all analyses to be a unique type of radio galaxies rather than a mixture of AGN and SFGs. They are dominated by a high-excitation radio galaxy population. We discuss environmental effects and scenarios for each sub-class. AGN tend to be preferentially located in locally dense environments and in the cores of clusters/groups, with these preferences persisting when comparing to galaxies of similar colour and stellar mass, suggesting that their activity may be ignited in the cluster/group virialized core regions. Conversely, SFGs exhibit a strong preference for intermediate-density global environments, suggesting that dusty starbursting activity in LSSs is largely driven by galaxy–galaxy interactions and merging.

We investigate the stellar kinematics and stellar populations of 58 radio-loud galaxies of intermediate luminosities (L-3 GHz > 10(23) W Hz(-1)) at 0.6 175 kms(-1), corresponding to black hole masses in excess of 10(8) M-circle dot. Furthermore, we confirm that at a fixed stellar mass the fraction of radio-loud AGN at z similar to 1 is five to 10 times higher than in the local universe, suggesting that quiescent, massive galaxies at z similar to 1 switch on as radio AGN on average once every Gyr. Our results strengthen the existing evidence for a link between high black hole masses, radio loudness, and quiescence at z similar to 1.

The Cl 1604 supercluster at z ~ 0.9 is one of the most extensively studied high-redshift large-scale structures, with more than 500 spectroscopically confirmed members. It consists of eight clusters and groups, with members numbering from a dozen to nearly a hundred, providing a broad range of environments for investigating the large-scale environmental effects on galaxy evolution. Here we examine the properties of 48 post-starburst galaxies in Cl 1604, comparing them to other galaxy populations in the same supercluster. Incorporating photometry from ground-based optical and near-infrared imaging, along with Spitzer mid-infrared observations, we derive stellar masses for all Cl 1604 members. The colors and stellar masses of the K+A galaxies support the idea that they are progenitors of red sequence galaxies. Their morphologies, residual star formation rates, and spatial distributions suggest that galaxy mergers may be the principal mechanism producing post-starburst galaxies. Interaction between galaxies and the dense intracluster medium (ICM) is also effective, but only in the cores of dynamically evolved clusters. The prevalence of post-starburst galaxies in clusters correlates with the dynamical state of the host cluster, as both galaxy mergers and the dense ICM produce post-starburst galaxies. We also investigate the incompleteness and contamination of K+A samples selected by means of Hδ and [O II] equivalent widths. K+A samples may be up to ~50% incomplete due to the presence of LINERs/Seyferts, and up to ~30% of K+A galaxies could have substantial star formation activity.

We measured the Tip of the Red Giant Branch distances to nine galaxies in the direction to the Virgo cluster using the Advanced Camera for Surveys on the Hubble Space Telescope. These distances put seven galaxies: GR 34, UGC 7512, NGC 4517, IC 3583, NGC 4600, VCC 2037 and KDG 215 in front of the Virgo, and two galaxies: IC 3023, KDG 177 likely inside the cluster. Distances and radial velocities of the galaxies situated between us and the Virgo core clearly exhibit the infall phenomenon toward the cluster. In the case of spherically symmetric radial infall we estimate the radius of the "zero-velocity surface" to be (7.2+-0.7) Mpc that yields the total mass of the Virgo cluster to be (8.0+-2.3) X 10^{14} M_sun in good agreement with its virial mass estimates. We conclude that the Virgo outskirts does not contain significant amounts of dark matter beyond its virial radius., Comment: 27 pages, 2 tables, 6 figures, accepted for publication in Astrophysical Journal