Explore the vast range of titles available.

Here we present a sample of 12 massive quiescent galaxy candidates at z ∼ 3 - 4 observed with the James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec). These galaxies were pre-selected from the Hubble Space Telescope imaging and 10 of our sources were unable to be spectroscopically confirmed by ground based spectroscopy. By combining spectroscopic data from NIRSpec with multi-wavelength imaging data from the JWST Near Infrared Camera (NIRCam), we analyse their stellar populations and their formation histories. We find that all of our galaxies classify as quiescent based on the reconstruction of their star formation histories but show a variety of quenching timescales and ages. All our galaxies are massive ( ∼ 0.1 - 1.2 × 10 11 M ⊙ ), with masses comparable to massive galaxies in the local Universe. We find that the oldest galaxy in our sample formed ∼ 1.0 × 10 11 M ⊙ of mass within the first few hundred million years of the Universe and has been quenched for more than a billion years by the time of observation at z ∼ 3.2 ( ∼ 2 billion years after the Big Bang). Our results point to very early formation of massive galaxies requiring a high conversion rate of baryons to stars in the early Universe.

We present the formation histories of 19 massive (≳3 × 1010M⊙) quiescent (specific star formation rate, sSFR < 0.15 Gyr−1) galaxy candidates at z ~ 3.0–4.5 observed using JWST/NIRSpec. This completes the spectroscopic confirmation of the 24 K-selected quiescent galaxy sample from the ZFOURGE and 3DHST surveys. Utilizing Prism 1–5 μm spectroscopy, we confirm that all 12 sources that eluded confirmation by ground-based spectroscopy lie at z > 3, resulting in a spectroscopically confirmed number density of ~1.4 × 10−5 Mpc−3 between z ~ 3 and 4. Rest-frame U − V versus V − J color selections show high effectiveness in identifying quiescent galaxies, with a purity of ~90%. Our analysis shows that parametric star formation histories (SFHs) from FAST++ and binned SFHs from Prospector on average yield consistent results, revealing diverse formation and quenching times. The oldest galaxy formed ~6 × 1010M⊙ by z ~ 10 and has been quiescent for over 1 Gyr at z ~ 3.2. We detect two galaxies with ongoing star formation and six with active galactic nuclei (AGNs). We demonstrate that the choice of stellar population models, stellar libraries, and nebular or AGN contributions does not significantly affect the derived average SFHs of the galaxies. We demonstrate that extending spectral fitting beyond the rest-frame optical regime reduces the inferred average star formation rates (SFRs) in the earliest time bins of the SFH reconstruction. The assumed SFH prior influences the SFR at early times, where spectral diagnostic power is limited. Simulated z ~ 3 quiescent galaxies from IllustrisTNG, SHARK, and Magneticum broadly match the average SFHs of the observed sample but struggle to capture the full diversity, particularly at early stages. Our results emphasize the need for mechanisms that rapidly build stellar mass and quench star formation within the first billion years of the Universe.

We present a new rest-frame color–color selection method using synthetic u s − g s and g s − i s , (ugi) s colors to identify star-forming and quiescent galaxies. Our method is similar to the widely used U − V versus V − J (UVJ) diagram. However, UVJ suffers known systematics. Spectroscopic campaigns have shown that UVJ-selected quiescent samples at z ≳ 3 include ∼10%–30% contamination from galaxies with dust-obscured star formation and strong emission lines. Moreover, at z > 3, UVJ colors are extrapolated because the rest-frame band shifts beyond the coverage of the deepest bandpasses at <5 μm (typically Spitzer/IRAC 4.5 μm or future JWST/NIRCam observations). We demonstrate that (ugi) s offers improvements to UVJ at z > 3, and can be applied to galaxies in the JWST era. We apply (ugi) s selection to galaxies at 0.5 < z < 6 from the (observed) 3D-HST and UltraVISTA catalogs, and to the (simulated) JAGUAR catalogs. We show that extrapolation can affect (V − J)0 color by up to 1 mag, but changes (gs−is)0 color by ≤0.2 mag, even at z ≃ 6. While (ugi) s -selected quiescent samples are comparable to UVJ in completeness (both achieve ∼85%–90% at z = 3–3.5), (ugi) s reduces contamination in quiescent samples by nearly a factor of 2, from ≃35% to ≃17% at z = 3, and from ≃60% to ≃33% at z = 6. This leads to improvements in the true-to-false-positive ratio (TP/FP), where we find TP/FP ≳2.2 for (ugi) s at z ≃ 3.5 − 6, compared to TP/FP < 1 for UVJ-selected samples. This indicates that contaminants will outnumber true quiescent galaxies in UVJ at these redshifts, while (ugi) s will provide higher-fidelity samples.

The measured ages of massive, quiescent galaxies at z ∼ 3–4 imply that massive galaxies quench as early as z ∼ 6. While the number of spectroscopic confirmations of quiescent galaxies at z < 3 has increased over the years, there are only a handful at z > 3.5. We report spectroscopic redshifts of one secure (z = 3.757) and two tentative (z = 3.336 and z = 4.673) massive ( log(M*/M⊙)>10.3 ) quiescent galaxies with 11 hr of Keck/MOSFIRE K-band observations. Our candidates were selected from the FLAMINGOS-2 Extragalactic Near-Infrared K-band Split (FENIKS) survey, which uses deep Gemini/Flamingos-2 K b K r imaging optimized for increased sensitivity to the characteristic red colors of galaxies at z > 3 with a strong Balmer/4000 Å break. The rest-frame UVJ and (ugi) s colors of three out of four quiescent candidates are consistent with 1–2 Gyr old stellar populations. This places these galaxies as the oldest objects at these redshifts, and challenges the notion that quiescent galaxies at z > 3 are all recently quenched, post-starburst galaxies. Our spectroscopy shows that the other quiescent-galaxy candidate is a broad-line active galactic nucleus (z = 3.594) with strong, redshifted Hβ + [O III] emission with a velocity offset > 1000 km s−1, indicative of a powerful outflow. The star formation history of our highest redshift candidate suggests that its progenitor was already in place by z ∼ 7–11, reaching ∼1011 M ⊙ by z ≃ 8. These observations reveal the limit of what is possible with deep near-infrared photometry and targeted spectroscopy from the ground and demonstrate that secure spectroscopic confirmation of quiescent galaxies at z > 4 is feasible only with JWST.

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.

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: AGEL1323 (M * ∼ 1011.1 M ⊙, z = 1.016, μ ∼ 14.6) and AGEL0014 (M * ∼ 1011.5 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 AGEL1323 and AGEL0014 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.

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 vcent=−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.

The formation of galaxies by gradual hierarchical co-assembly of baryons and cold dark matter halos is a fundamental paradigm underpinning modern astrophysics 1 , 2 and predicts a strong decline in the number of massive galaxies at early cosmic times 3 – 5 . Extremely massive quiescent galaxies (stellar masses of more than 10 11   M ⊙ ) have now been observed as early as 1–2 billion years after the Big Bang 6 – 13 . These galaxies are extremely constraining on theoretical models, as they had formed 300–500 Myr earlier, and only some models can form massive galaxies this early 12 , 14 . Here we report on the spectroscopic observations with the JWST of a massive quiescent galaxy ZF-UDS-7329 at redshift 3.205 ± 0.005. It has eluded deep ground-based spectroscopy 8 , it is significantly redder than is typical and its spectrum reveals features typical of much older stellar populations. Detailed modelling shows that its stellar population formed around 1.5 billion years earlier in time ( z ≈ 11) at an epoch when dark matter halos of sufficient hosting mass had not yet assembled in the standard scenario 4 , 5 . This observation may indicate the presence of undetected populations of early galaxies and the possibility of significant gaps in our understanding of early stellar populations, galaxy formation and the nature of dark matter. A massive galaxy observed with the JWST indicates that the bulk of its stars formed within the first 500 million years of the Universe.

We study the spatially resolved outflow properties of CSWA13, an intermediate-mass (M* = 109 M⊙), gravitationally lensed star-forming galaxy at z = 1.87. We use Keck/KCWI to map outflows in multiple rest-frame UV interstellar medium (ISM) absorption lines, along with fluorescent Si ii* emission, and nebular emission from C iii] tracing the local systemic velocity. The spatial structure of the outflow velocity mirrors that of the nebular kinematics, which we interpret to be a signature of a young galactic wind that is pressurizing the ISM of the galaxy but is yet to burst out. From the radial extent of Si ii* emission, we estimate that the outflow is largely encapsulated within 3.5 kpc. We explore the geometry (e.g., patchiness) of the outflow by measuring the covering fraction at different velocities, finding that the maximum covering fraction is at velocities v ≃ −150 km s−1. Using the outflow velocity (vout), radius (R), column density (N), and solid angle (Ω) based on the covering fraction, we measure the mass-loss rate logṁout/(M⊙yr−1)=1.73±0.23 and mass loading factor logη=0.04±0.34 for the low-ionization outflowing gas in this galaxy. These values are relatively large and the bulk of the outflowing gas is moving with speeds less than the escape velocity of the galaxy halo, suggesting that the majority of the outflowing mass will remain in the circumgalactic medium and/or recycle back into the galaxy. The results support a picture of high outflow rates transporting mass and metals into the inner circumgalactic medium, providing the gas reservoir for future star formation.

A massive ancient galaxy with minimal star formation is observed spectroscopically at an epoch when the Universe is less than 2 billion years old, posing a challenge to theories. Galaxies prematurely aged Deep astronomical surveys have provided evidence for groups of massive, quiescent galaxies at high redshifts, but this poses a problem: theoretical models do not account for galaxies that stopped forming stars so early in the history of the Universe. Detecting such galaxies is an observational challenge owing to their negligible rest-frame ultraviolet emission and the need for extremely deep near-infrared surveys—the evidence has so far consisted entirely of coarsely sampled photometry. Karl Glazebrook et al . report spectroscopic confirmation of one of these galaxies at a redshift of 3.717, with a stellar mass of 1.7 × 10 11 solar masses. The absorption line spectrum shows no current star-formation, and the age of the galaxy is derived to be nearly half that of the Universe. The authors suggest that the galaxy formed its stars in an extreme and short starburst within the first billion years of cosmic history, implying that our picture of galaxy formation may need an update. Finding massive galaxies that stopped forming stars in the early Universe presents an observational challenge because their rest-frame ultraviolet emission is negligible and they can only be reliably identified by extremely deep near-infrared surveys. These surveys have revealed the presence of massive, quiescent early-type galaxies 1 , 2 , 3 , 4 , 5 , 6 appearing as early as redshift z  ≈ 2, an epoch three billion years after the Big Bang. Their age and formation processes have now been explained by an improved generation of galaxy-formation models 7 , 8 , 9 , in which they form rapidly at z  ≈ 3–4, consistent with the typical masses and ages derived from their observations. Deeper surveys have reported evidence for populations of massive, quiescent galaxies at even higher redshifts and earlier times, using coarsely sampled photometry. However, these early, massive, quiescent galaxies are not predicted by the latest generation of theoretical models 7 , 8 , 9 , 10 . Here we report the spectroscopic confirmation of one such galaxy at redshift z  = 3.717, with a stellar mass of 1.7 × 10 11 solar masses. We derive its age to be nearly half the age of the Universe at this redshift and the absorption line spectrum shows no current star formation. These observations demonstrate that the galaxy must have formed the majority of its stars quickly, within the first billion years of cosmic history in a short, extreme starburst. This ancestral starburst appears similar to those being found by submillimetre-wavelength surveys 11 , 12 , 13 , 14 . The early formation of such massive systems implies that our picture of early galaxy assembly requires substantial revision.