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 −1 of galaxies at 0.6 z 1.0, each observed for ∼20 hr 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 (HδA ∼ 5 ), while passive galaxies have higher observed stellar velocity dispersions (∼200 km s−1) and weak Hδ absorption (HδA ∼ 0 ). Strong O III5007/Hβ ratios tend to occur mostly for galaxies with weak HδA or galaxies with higher observed velocity dispersion. Beyond these broad trends, we find a 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.
ABSTRACT
We use a sample of z = 0 galaxies visually classified as slow rotators (SRs) in the eagle hydrodynamical simulations to explore the effect of galaxy mergers on their formation, characterize ...their intrinsic galaxy properties, and study the connection between quenching and kinematic transformation. SRs that have had major or minor mergers (mass ratios ≥0.3 and 0.1−0.3, respectively) tend to have a higher triaxiality parameter and ex-situ stellar fractions than those that had exclusively very minor mergers or formed in the absence of mergers (‘no-merger’ SRs). No-merger SRs are more compact, have lower black hole-to-stellar mass ratios and quenched later than other SRs, leaving imprints on their z = 0 chemical composition. For the vast majority of SRs we find that quenching, driven by active galactic nuclei feedback, precedes kinematic transformation, except for satellite SRs, in which these processes happen in tandem. However, in ≈50 per cent of these satellites, satellite–satellite mergers are responsible for their SR fate, while environment (i.e. tidal field and interactions with the central) can account for the transformation in the rest. By splitting SRs into kinematic sub-classes, we find that flat SRs prefer major mergers; round SRs prefer minor or very minor mergers; prolate SRs prefer gas-poor mergers. Flat and prolate SRs are more common among satellites hosted by massive haloes ($\gt 10^{13.6}\, \rm M_{\odot }$) and centrals of high masses ($M_{\star } \gt 10^{10.5}\, \rm M_{\odot }$). Although eagle galaxies display kinematic properties that broadly agree with observations, there are areas of disagreement, such as inverted stellar age and velocity dispersion profiles. We discuss these and how upcoming simulations can solve them.
ABSTRACT
Most dynamical models of galaxies to date assume axisymmetry, which is not representative of a significant fraction of massive galaxies. We have built triaxial orbit-superposition ...Schwarzschild models of galaxies observed by the SAMI Galaxy Survey, in order to reconstruct their inner orbital structure and mass distribution. The sample consists of 153 passive galaxies with total stellar masses in the range 109.5 to $10^{12} \, {\rm M}_{\odot }$. We present an analysis of the internal structures and intrinsic properties of these galaxies as a function of their environment. We measure their environment using three proxies: central or satellite designation, halo mass and local 5th nearest neighbour galaxy density. We find that although these intrinsic properties correlate most strongly with stellar mass, environment does play a secondary role: at fixed stellar mass, galaxies in the densest regions are more radially anisotropic. In addition, central galaxies, and galaxies in high local densities show lower values of edge-on spin parameter proxy λRe, EO. We also find suggestions of a possible trend of the fractions of orbits with environment for lower mass galaxies (between 109.5 and $10^{11} \, {\rm M}_{\odot }$) such that, at fixed stellar mass, galaxies in higher local densities and halo mass have higher fractions of hot orbits and lower fractions of warm orbits. Our results demonstrate that after stellar mass, environment does play a role in shaping present-day passive galaxies.
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 ...break (Dn4000) and Balmer absorption line strengths (probed by Hδ) from 1019 high-quality spectra of z = 0.6-1.0 galaxies with M* = 2 × 1010M to 3 × 1011M . 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 Dn4000-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 × 1010M , we see a bimodal Dn4000-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 × 1011M 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 >1011M 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 Dn4000, implying larger short-term variations in star formation activity.
ABSTRACT
We use data from the Sydney-AAO Multi-object Integral-field spectroscopy (SAMI) Galaxy Survey to study the dynamical scaling relation between galaxy stellar mass M∗ and the general kinematic ...parameter $S_K = \sqrt{K V_{\rm rot}^2 + \sigma ^2}$ that combines rotation velocity Vrot and velocity dispersion σ. We show that the log M∗ – log SK relation: (1) is linear above limits set by properties of the samples and observations; (2) has slightly different slope when derived from stellar or gas kinematic measurements; (3) applies to both early-type and late-type galaxies and has smaller scatter than either the Tully–Fisher relation (log M∗ − log Vrot) for late types or the Faber–Jackson relation (log M∗ − log σ) for early types; and (4) has scatter that is only weakly sensitive to the value of K, with minimum scatter for K in the range 0.4 and 0.7. We compare SK to the aperture second moment (the ‘aperture velocity dispersion’) measured from the integrated spectrum within a 3-arcsecond radius aperture ($\sigma _{3^{\prime \prime }}$). We find that while SK and $\sigma _{3^{\prime \prime }}$ are in general tightly correlated, the log M∗ − log SK relation has less scatter than the $\log M_* - \log \sigma _{3^{\prime \prime }}$ relation.
Cosmological hydrodynamical simulations are rich tools to understand the build-up of stellar mass and angular momentum in galaxies, but require some level of calibration to observations. We compare ...predictions at |$z$| ∼ 0 from the eagle, hydrangea, horizon-agn, and magneticum simulations with integral field spectroscopic (IFS) data from the SAMI (Sydney-AAO Multi-object Integral field spectrograph) Galaxy Survey, ATLAS^3D, CALIFA (Calar Alto Legacy Integral Field Area), and MASSIVE surveys. The main goal of this work is to simultaneously compare structural, dynamical, and stellar population measurements in order to identify key areas of success and tension. We have taken great care to ensure that our simulated measurement methods match the observational methods as closely as possible, and we construct samples that match the observed stellar mass distribution for the combined IFS sample. We find that the eagle and hydrangea simulations reproduce many galaxy relations but with some offsets at high stellar masses. There are moderate mismatches in R_e (+), ε (−), σ_e (−), and mean stellar age (+), where a plus sign indicates that quantities are too high on average, and minus sign too low. The horizon-agn simulations qualitatively reproduce several galaxy relations, but there are a number of properties where we find a quantitative offset to observations. Massive galaxies are better matched to observations than galaxies at low and intermediate masses. Overall, we find mismatches in R_e (+), ε (−), σ_e (−), and (V/σ)_e (−). magneticum matches observations well: this is the only simulation where we find ellipticities typical for disc galaxies, but there are moderate differences in σ_e (−), (V/σ)_e (−), and mean stellar age (+). Our comparison between simulations and observational data has highlighted several areas for improvement, such as the need for improved modelling resulting in a better vertical disc structure, yet our results demonstrate the vast improvement of cosmological simulations in recent years.
ABSTRACT
We have entered a new era where integral-field spectroscopic surveys of galaxies are sufficiently large to adequately sample large-scale structure over a cosmologically significant volume. ...This was the primary design goal of the SAMI Galaxy Survey. Here, in Data Release 3, we release data for the full sample of 3068 unique galaxies observed. This includes the SAMI cluster sample of 888 unique galaxies for the first time. For each galaxy, there are two primary spectral cubes covering the blue (370–570 nm) and red (630–740 nm) optical wavelength ranges at spectral resolving power of R = 1808 and 4304, respectively. For each primary cube, we also provide three spatially binned spectral cubes and a set of standardized aperture spectra. For each galaxy, we include complete 2D maps from parametrized fitting to the emission-line and absorption-line spectral data. These maps provide information on the gas ionization and kinematics, stellar kinematics and populations, and more. All data are available online through Australian Astronomical Optics Data Central.
We use integral-field spectroscopy from the SAMI Galaxy Survey to identify galaxies that show evidence of recent quenching of star formation. The galaxies exhibit strong Balmer absorption in the ...absence of ongoing star formation in more than 10% of their spectra within the SAMI field of view. These -strong (HDS) galaxies (HDSGs) are rare, making up only ∼2% (25/1220) of galaxies with stellar mass > 10. The HDSGs make up a significant fraction of nonpassive cluster galaxies (15%; 17/115) and a smaller fraction (2.0%; 8/387) of the nonpassive population in low-density environments. The majority (9/17) of cluster HDSGs show evidence of star formation at their centers, with the HDS regions found in the outer parts of the galaxy. Conversely, the HDS signal is more evenly spread across the galaxy for the majority (6/8) of HDSGs in low-density environments and is often associated with emission lines that are not due to star formation. We investigate the location of the HDSGs in the clusters, finding that they are exclusively within 0.6R200 of the cluster center and have a significantly higher velocity dispersion relative to the cluster population. Comparing their distribution in projected phase space to those derived from cosmological simulations indicates that the cluster HDSGs are consistent with an infalling population that has entered the central 0.5r200,3D cluster region within the last ∼1 Gyr. In the eight of nine cluster HDSGs with central star formation, the extent of star formation is consistent with that expected of outside-in quenching by ram pressure stripping. Our results indicate that the cluster HDSGs are currently being quenched by ram pressure stripping on their first passage through the cluster.
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 10-20 kpc, or to an average of 2.7Re. Combined with central stellar velocity dispersions ( 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 × 1011 M ) generally show no or little rotation measured at 5 kpc ( V 5 0 < 0.2 in eight of ten 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 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 Calar Alto Legacy Integral Field Area (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 5 kpc 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.
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