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.
Stellar population parameters correlate with a range of galaxy properties, but it is unclear which relations are causal and which are the result of another underlying trend. In this series, we ...quantitatively compare trends between stellar population properties and galaxy structural parameters in order to determine which relations are intrinsically tighter, and are therefore more likely to reflect a causal relation. Specifically, we focus on the galaxy structural parameters of mass M, gravitational potential , and surface mass density . In Barone et al. we found that for early-type galaxies (ETGs) the age- and Z/H-Φ relations show the least intrinsic scatter as well as the least residual trend with galaxy size. In this work we study the ages and metallicities measured from full spectral fitting of 2085 star-forming galaxies (SFGs) from the SDSS Legacy Survey, selected so all galaxies in the sample are probed to one effective radius. As with the trends found in ETGs, we find that in SFGs age correlates best with stellar surface mass density, and Z/H correlates best with gravitational potential. We discuss multiple mechanisms that could lead to these scaling relations. For the Z/H-Φ relation we conclude that gravitational potential is the primary regulator of metallicity, via its relation to the gas escape velocity. The age- relation is consistent with compact galaxies forming earlier, as higher gas fractions in the early universe cause old galaxies to form more compactly during their in situ formation phase, and may be reinforced by compactness-related quenching mechanisms.
Abstract
We present spectroscopic confirmation of candidate strong gravitational lenses using the Keck Observatory and Very Large Telescope as part of our
ASTRO 3D Galaxy Evolution with Lenses
(
AGEL
...) survey. We confirm that (1) search methods using convolutional neural networks (CNNs) with visual inspection successfully identify strong gravitational lenses and (2) the lenses are at higher redshifts relative to existing surveys due to the combination of deeper and higher-resolution imaging from DECam and spectroscopy spanning optical to near-infrared wavelengths. We measure 104 redshifts in 77 systems selected from a catalog in the
DES
and
DECaLS
imaging fields (
r
≤ 22 mag). Combining our results with published redshifts, we present redshifts for 68 lenses and establish that CNN-based searches are highly effective for use in future imaging surveys with a success rate of at least 88% (defined as 68/77). We report 53 strong lenses with spectroscopic redshifts for both the deflector and source (
z
src
>
z
defl
), and 15 lenses with a spectroscopic redshift for either the deflector (
z
defl
> 0.21) or source (
z
src
≥ 1.34). For the 68 lenses, the deflectors and sources have average redshifts and standard deviations of 0.58 ± 0.14 and 1.92 ± 0.59 respectively, and corresponding redshift ranges of
z
defl
= 0.21–0.89 and
z
src
= 0.88–3.55. The
AGEL
systems include 41 deflectors at
z
defl
≥ 0.5 that are ideal for follow-up studies to track how mass density profiles evolve with redshift. Our goal with
AGEL
is to spectroscopically confirm ∼100 strong gravitational lenses that can be observed from both hemispheres throughout the year. The
AGEL
survey is a resource for refining automated all-sky searches and addressing a range of questions in astrophysics and cosmology.
Abstract Observed evolution of the total mass distribution with redshift is crucial to testing galaxy evolution theories. To measure the total mass distribution, strong gravitational lenses ...complement the resolved dynamical observations that are currently limited to z ≲ 0.5. Here we present the lens models for a pilot sample of seven galaxy-scale lenses from the ASTRO3D Galaxy Evolution with Lenses ( AGEL ) survey. The AGEL lenses, modeled using HST/WFC3-F140W images with Gravitational Lens Efficient Explorer ( GLEE ) software, have deflector redshifts in the range 0.3 < z defl < 0.9. Assuming a power-law density profile with slope γ , we measure the total density profile for the deflector galaxies via lens modeling. We also measure the stellar velocity dispersions ( σ obs ) for four lenses and obtain σ obs from SDSS - BOSS for the remaining lenses to test our lens models by comparing observed and model-predicted velocity dispersions. For the seven AGEL lenses, we measure an average density profile slope of −1.95 ± 0.09 and a γ – z relation that does not evolve with redshift at z < 1. Although our result is consistent with some observations and simulations, it differs from other studies at z < 1 that suggest the γ – z relation evolves with redshift. The apparent conflicts among observations and simulations may be due to a combination of (1) systematics in the lensing and dynamical modeling; (2) challenges in comparing observations with simulations; and (3) assuming a simple power law for the total mass distribution. By providing more lenses at z defl > 0.5, the AGEL survey will provide stronger constraints on whether the mass profiles evolve with redshift as predicted by current theoretical models.
Abstract
We study the kinematics of the interstellar medium (ISM) viewed “down the barrel” in 20 gravitationally lensed galaxies during cosmic noon (
z
= 1.5–3.5). We use moderate-resolution spectra ...(
R
∼ 4000) from Keck’s Echellette Spectrograph and Imager and Magellan/MagE to spectrally resolve the ISM absorption in these galaxies into ∼10 independent elements and use double Gaussian fits to quantify the velocity structure of the gas. We find that the bulk motion of gas in this galaxy sample is outflowing, with average velocity centroid
v
cent
=
−
141
km s
−1
(±111 km s
−1
scatter) measured with respect to the systemic redshift. A total of 16 out of the 20 galaxies exhibit a clear positive skewness, with a blueshifted tail extending to ∼ −500 km s
−1
. We examine scaling relations in outflow velocities with galaxy stellar mass and star formation rate, finding correlations consistent with a momentum-driven wind scenario. Our measured outflow velocities are also comparable to those reported for FIRE-2 and TNG50 cosmological simulations at similar redshift and galaxy properties. We also consider implications for interpreting results from lower-resolution spectra. We demonstrate that while velocity centroids are accurately recovered, the skewness, velocity width, and probes of high-velocity gas (e.g.,
v
95
) are subject to large scatter and biases at lower resolution. We find that
R
≳ 1700 is required for accurate results for the gas kinematics of our sample. This work represents the largest available sample of well-resolved outflow velocity structure at
z
> 2 and highlights the need for good spectral resolution to recover accurate properties.
ABSTRACT
We study the internal radial gradients of the stellar populations in a sample comprising 522 early-type galaxies (ETGs) from the SAMI (Sydney-AAO Multi-object Integral field spectrograph) ...Galaxy Survey. We stack the spectra of individual spaxels in radial bins, and derive basic stellar population properties: total metallicity (Z/H), Mg/Fe, C/Fe and age. The radial gradient (∇) and central value of the fits (evaluated at Re/4) are compared against a set of six observables that may act as drivers of the trends. We find that velocity dispersion (σ) – or, equivalently gravitational potential – is the dominant driver of the chemical composition gradients. Surface mass density is also correlated with the trends, especially with stellar age. The decrease of ∇Mg/Fe with increasing σ is contrasted by a rather shallow dependence of ∇Z/H with σ (although this radial gradient is overall rather steep). This result, along with a shallow age slope at the massive end, imposes a substantial constraint on the progenitors of the populations that contribute to the formation of the outer envelopes of ETGs. The SAMI sample is split, by design, between ‘field’ and cluster galaxies. Only weak environment-related differences are found, most notably a stronger dependence of central total metallicity (Z/He4) with σ, along with a marginal trend of ∇Z/H to steepen in cluster galaxies, a result that is not followed by Mg/Fe. The results presented here serve as stringent constraints on numerical models of the formation and evolution of ETGs.
ABSTRACT While most galaxies live in group environments where they undergo an accelerated evolution, the characteristics of their circumgalactic medium (CGM) remain uncertain. We present an analysis ...of the CGM of two galaxy groups in different stages of interaction: (G1) a close pair of galaxies (z = 0.043) separated by 87 kpc that do not show signs of interactions and (G2) four merging galaxies (z = 0.098) separated by 10 kpc. We present spatially resolved Keck/Keck Cosmic Web Imager galaxy observations and Hubble Space Telescope (HST)/COS quasar spectra (G1 at 48 kpc and G2 at 100 kpc away) to quantify both the resolved galaxy and CGM properties in these two different group environments. G1 contains two typical star-forming galaxies with no evidence of strong outflows. G2 contains two star-forming, one post-starburst and one quiescent galaxy. Both groups have a range of CGM-detected metal lines (H i, C ii, Si ii, Si iii, N v, and O vi). Despite G2 being twice as far from the quasar, G2 has $\log (N({{{\rm H}{\small I}}})/{\rm cm}^{-2})=17.33$, compared to $\log (N({{{\rm H}{\small I}}})/{\rm cm}^{-2})=16.43$ for G1. We find that the CGM of the merging galaxies (G2) is more kinematically complex, is in a higher ionization state, spans a wider range of metallicities and column densities, has smaller cloud sizes, and is inconsistent with the simple superposition model that seems to match well with G1. We conclude that the complexity of the CGM in merging galaxies surpasses that of not strongly interacting galaxies, suggesting that mergers play a significant role in shaping the intricate structure of the CGM.
Abstract
Gravitational lenses can magnify distant galaxies, allowing us to discover and characterize the stellar populations of intrinsically faint, quiescent galaxies that are otherwise extremely ...difficult to directly observe at high redshift from ground-based telescopes. Here, we present the spectral analysis of two lensed, quiescent galaxies at
z
≳ 1 discovered by the
ASTRO 3D Galaxy Evolution with Lenses
survey:
AGEL
1323 (
M
*
∼ 10
11.1
M
⊙
,
z
= 1.016,
μ
∼ 14.6) and
AGEL
0014 (
M
*
∼ 10
11.5
M
⊙
,
z
= 1.374,
μ
∼ 4.3). We measured the age, Fe/H, and Mg/Fe of the two lensed galaxies using deep, rest-frame-optical spectra (S/N ≳40 Å
−1
) obtained on the Keck I telescope. The ages of
AGEL
1323 and
AGEL
0014 are
5.6
−
0.8
+
0.8
Gyr and
3.1
−
0.3
+
0.8
Gyr, respectively, indicating that most of the stars in the galaxies were formed less than 2 Gyr after the Big Bang. Compared to nearby quiescent galaxies of similar masses, the lensed galaxies have lower Fe/H and Mg/H. Surprisingly, the two galaxies have comparable Mg/Fe to similar-mass galaxies at lower redshifts, despite their old ages. Using a simple analytic chemical evolution model connecting the instantaneously recycled element Mg with the mass-loading factors of outflows averaged over the entire star formation history, we found that the lensed galaxies may have experienced enhanced outflows during their star formation compared to lower-redshift galaxies, which may explain why they quenched early.
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