Mariska Kriek

Quiescent galaxies in the distant Universe exhibit a range of gas content that may indicate a variety of quenching processes are at play. Mapping the distribution and kinematics of the gas can illuminate its origins, but nearly all such observations have been unresolved. We present JWST/NIRSpec integral field unit (IFU) observations of MRG-M0138, a gravitationally lensed, massive quiescent galaxy at z ∼ 2 observed as part of the INQUEST-JWST survey. We use Na i D absorption, which we detect in excess of the stellar absorption over most of the galaxy, to trace the kinematics and spatial distribution of the neutral gas in 219 spatial bins. The gas exhibits clear rotation that is kinematically aligned with the stellar disk. Both the gas and dust have a complex spatial structure, including an off-nuclear clump, a dust lane, and patches in the outer disk. The nonequilibrium distribution suggests that the gas was accreted. Analysis of the galaxy’s star formation history (SFH) supports this interpretation by indicating a rejuvenation event 500 Myr ago. We identify two plausibly associated galaxies and suggest that tidal interactions are a likely source of the accreted gas. Our results indicate that some of the variation in gas content among early quiescent galaxies is not related to differences in gas consumption timescales. The detection of a gas clump at a projected distance of ∼90 pc from the known supermassive black hole illustrates a mechanism to fuel the episodic active galactic nucleus (AGN) feedback that may maintain quiescence.

The formation of massive galaxies remains a fundamental question in astrophysics, with recent JWST observations suggesting that intense star formation occurred earlier than previously expected. We used the prototypical massive relic galaxy NGC,1277 as a fossil record to probe the chemical signatures of early star formation. With a stellar mass of 1.2 =1.05^ and a compact structure (half-light radius of 1.2,kpc), NGC,1277 is representative of massive relic galaxies—systems that formed rapidly at high redshifts (`red nuggets' at z > 2) and have since undergone largely passive evolution, preserving the imprint of their earliest stellar populations. Using deep near-infrared spectroscopy, we identified unusually strong silicon (Si) absorption features in this galaxy. We measure Si/Fe +0.45 _ -0.27 and Mg/Fe =0.36^ +0.27 _ -0.24 , corresponding to a significantly enhanced silicon-to-magnesium ratio ( Si/Mg =0.67^ +0.45 _ -0.27 ), which cannot be reproduced by current stellar population models or typical core-collapse supernova yields. This enhancement suggests a contribution from very massive, metal-poor progenitors during the earliest phases of star formation. Such conditions are consistent with nucleosynthetic yields from pair-instability supernovae or other enrichment channels associated with extremely massive stars, whose chemical signatures are expected to remain less diluted in systems like NGC,1277 due to their rapid formation timescales and minimal late-time accretion. This result provides rare chemical evidence of early massive-star enrichment preserved in a local relic galaxy and opens a new observational window into the chemical evolution of the Universe.

Spatially resolved stellar populations of massive quiescent galaxies at cosmic noon provide powerful insights into star-formation quenching and stellar mass assembly mechanisms. Previous photometric studies have revealed that the cores of these galaxies are redder than their outskirts. However, spectroscopy is needed to break the age-metallicity degeneracy and uncover the driver of these colour gradients. In this work, we derive the age and elemental abundance gradients for eight distant (1.2 ≲ z ≲ 2.2), massive (10.3 ≲ log( M _* /M _⊙ )≲11.1) quiescent galaxies by fitting full-spectrum models to ultra-deep NIRSpec-MSA spectroscopy from the JWST -SUSPENSE survey. We find that these galaxies have negative age and flat [Fe/H] gradients as well as tentative indications of positive [Mg/H] and [Mg/Fe] gradients. These results suggest that galaxy cores are older and perhaps also Mg deficient compared to galaxy outskirts. The age gradients may indicate inside-out quenching, while Mg-deficient cores could suggest rapid gas expulsion as the central quenching mechanism. Thus, galaxy cores may have formed faster and quenched more efficiently than their outskirts. In this scenario, however, our [Fe/H] and [Mg/Fe] gradients are still puzzling, and further investigation is required to understand the nature of [Mg/H] gradients in massive quiescent galaxies at these redshifts. Our results contrast with those of lower-redshift studies, which find flat age and [Mg/Fe] gradients and negative metallicity gradients. Additionally, we find a positive trend between age gradients and rotational support and marginal trends between [Fe/H] gradients and galaxy velocity dispersions and ages. We discuss our findings in the context of galaxy growth scenarios, including minor mergers and progenitor bias. With this work, we present the first stellar population gradients from NIRSpec-MSA spectroscopy in the current largest sample of distant quiescent galaxies.

We present detections of auroral emission lines of [O iii ], [O ii ], [S iii ], and [S ii ] in deep JWST/NIRSpec spectroscopy for 41 star-forming galaxies at z = 1.4–7.2 from the AURORA survey. We combine these new observations with 98 star-forming galaxies at z = 1.3–10.6 with detected auroral lines drawn from the literature to form a sample of 139 high-redshift galaxies with robust electron temperature and direct-method oxygen abundance determinations. This sample notably covers a wider dynamic range in metallicity than previous work, spanning 0.02–0.9 Z _⊙ . We calibrate empirical relations between 19 emission-line ratios and oxygen abundance, providing a robust tool set to infer accurate gas-phase metallicities of high-redshift galaxies when auroral lines are not detected. While calibrations based on lines of α elements (O, Ne, S, Ar) appear reliable, we find significant scatter in calibrations involving lines of N driven by a high dispersion in N/O at fixed O/H, suggesting that N-based line ratios are less reliable tracers of the oxygen abundance at high redshift. These new high-redshift calibrations are notably offset from those based on typical z ∼ 0 galaxy and H ii region samples, and are better matched by samples of extreme local galaxies that are analogs of high-redshift sources. The new metallicity calibrations presented in this work pave the way for robust studies of galaxy chemical evolution in the early Universe, leading to a better understanding of baryon cycling and galaxy formation from Cosmic Noon through the Epoch of Reionization.

Many poststarburst galaxies at z ∼ 0.7 have been shown to retain substantial molecular gas reservoirs yet host low ongoing star formation, suggesting that the remaining gas may be inefficient at forming stars during the early postburst phase. We present new Atacama Large Millimeter/submillimeter Array CO(5–4) observations of nine gas-rich poststarburst galaxies at z ∼ 0.7 from the Studying Quenching in Intermediate- z Galaxies: Gas, angu L → ar momentum, and Evolution (SQuIGG L → E) survey, providing a view of the molecular gas excitation in these systems. Combined with existing CO(2–1) data, we detect CO(5–4) in eight out of nine targets and find that most have moderate CO excitation with r 52 ≡ L CO ( 5 − 4 ) ′ / L CO ( 2 − 1 ) ′ ≈ 0.1 − 0.3 . These systems show no clear trend between r ₅₂ and either total or surface-density of star formation. Specifically, all objects have Σ _SFR ∼ 0.01–1 M _⊙ yr ⁻¹ kpc ⁻² , consistent with compact, modest star formation, even when allowing for buried activity, as these galaxies decline from their peak. One object, J1448+1010, which has clear optical, mid-infrared, and radio indicators of an active galactic nucleus, is an outlier with r ₅₂ ≈ 0.6; its elevated excitation likely requires significant nonstellar heating, with a contribution from potentially obscured star formation. Together, most gas-rich SQuIGG L → E poststarbursts have moderately excited molecular gas alongside little to modest star-forming activity, indicating that the remaining gas hosts relatively suppressed star formation efficiencies instead of strong buried starburst activity.

We present spatially resolved rest-frame optical emission line maps of four galaxies at z ∼ 2 observed with the Keck/OH-Suppressing Infra-Red Imaging Spectrograph to study the physical conditions of the interstellar medium (ISM) at cosmic noon. Our analysis of strong emission line ratios in these galaxies reveals an offset from the local star-forming locus on the Baldwin–Phillips–Terlevich diagram but agrees with other star-forming galaxies at similar redshifts. Despite the offset toward higher [O iii ] λ 5008/H β and [N ii ] λ 6585/H α , these strong line ratios remain consistent with or below the maximum starburst threshold even in the inner ∼1 kpc region of the galaxies, providing no compelling evidence for central active galactic nucleus activity. The galaxies also exhibit flat radial gas-phase metallicity gradients, consistent with previous studies of z ∼ 2 galaxies and suggesting efficient radial mixing possibly driven by strong outflows from intense star formation. Overall, our results reveal the highly star-forming nature of these galaxies, with the potential to launch outflows that flatten metallicity gradients through significant radial gas mixing. Future observations with JWST/NIRSpec are crucial to detect fainter emission lines at higher spatial resolution to further constrain the physical processes and ionization mechanisms that shape the ISM during cosmic noon.

We derive the Tully-Fisher (TFR; M _* − V _circ, f ) and Fall (FR; j _* − M _* ) relations at redshift z = 0.9 using a sample of 43 main-sequence disc galaxies with H α IFU data and JWST/HST imaging. The strength of our analysis lies in the use of state-of-the-art 3D kinematic models to infer galaxy rotation curves, the inclusion of near-IR bands and their morphological modelling, and the application of homogeneous spectral energy distribution modelling to our photometry measurements to estimate stellar masses. After correcting the inferred H α velocities for asymmetric drift, we find a TFR of the form log( M _* / M _⊙ ) = a log( V _circ,f / 150 km s ⁻¹ + b , with a = 3.82 _−0.40 ^+0.55 and b = 10.27 _−0.07 ^+0.06 , as well as a FR of the form log( j _* /kpc km s ⁻¹ ) = a log( M _* /10 ^10.5 M _⊙ )+ b , with a = 0.44 _−0.06 ^+0.06 and b = 2.86 _−0.02 ^+0.02 . Compared with their z = 0 counterparts, we found moderate evolution in the TFR and strong evolution in the FR over the past 8 Gyr. We interpreted our findings in the context of the galaxy-to-halo scaling parameters f _M = M _* / M _vir and f _j = j _* / j _vir . We inferred that f _j shows little redshift evolution and depends very weakly on M _* , with typical values around f _j ∼ 0.8. As for f _M , we find it to be higher and less dependent on M _* at z = 0.9 than at z = 0. We discuss how interpreting our observed f _M − M _* relations within the cold dark matter framework implies necessarily that the galaxy populations at z = 0.9 and z = 0 are not the progenitor nor descendant of one another. The alternative scenario is that the z = 0.9 scaling relations are incorrect due to strong selection effects, unidentified systematics, or the possibility that H α kinematics may not be a reliable dynamical tracer. Such problems would affect not only our work but also previous studies on the same subject.

Observational and theoretical studies have long held that rapid gas consumption in starbursts is responsible for the formation of the most massive quiescent galaxies at high redshift. However, studies of recently quenched “post-starburst” galaxies have discovered that a number of them are surprisingly luminous in CO, challenging this assumption. We present deep Atacama Large Millimeter/submillimeter Array CO(2–1) observations of 50 massive ( log ( M ⋆ / M ⊙ ) ∼ 11.2 ) post-starburst galaxies from the SQuIGG L → E sample at z ∼ 0.7. We detect a large fraction (27/50) of the galaxies in CO(2–1). We perform new spectral energy distribution (SED) fits incorporating mid- and far-IR photometry to measure the star formation rates (SFRs) and histories that can reproduce both the rest-optical and dust properties of these galaxies. We find that the CO luminosity correlates with the age of the recent starburst, suggesting a gas-removal timescale of ≲150 Myr, an order of magnitude shorter than is implied by their SFRs under standard birth cloud dust assumptions. We find that while allowing for significantly more attenuation in birth clouds can raise SFRs by ∼0.5 dex, for almost all galaxies, it is neither required to fit the observed IR SED, nor is it sufficient to explain the observed depletion trend. Even the combination of significant buried star formation and ULIRG-like α _CO is not enough to explain this decay in CO luminosity. Furthermore, there is no strong evidence to support either of those modifications to the depletion time. Therefore, it remains a distinct possibility that the age–CO luminosity trend should not be interpreted as an evolutionary sequence, and that gas-rich SQuIGG L → E galaxies will soon rejuvenate.

Tracking the cold molecular gas contents of galaxies is critical to understand the interplay between star formation and galaxy growth across cosmic time. Observations of the long-wavelength dust continuum, a proxy for the cold gas, are widely used in the high-redshift community because of their ease and efficiency. These measurements rely on the assumption of a molecular gas-to-dust mass ratio, typically taken to be δ _GDR ≈ 100 in massive, metal-rich systems. We present Atacama Large Millimeter/submillimeter Array observations of the 870 μ m dust continuum in a sample of five massive quiescent galaxies at z ∼ 1 with existing detections of CO(2–1). We find surprisingly weak dust emission, falling a factor of ≳0.4–0.8 dex below the typical correlation between CO and continuum luminosity. We interpret this dust deficiency as evidence for unusually high δ _GDR in these galaxies, which we calculate to range from 300 to at least 1200. Our results and other observations from the literature are generally compatible with predictions from the SIMBA cosmological simulation that dust is preferentially destroyed in quiescent galaxies. Ultimately, we conclude that the dust continuum is a highly unreliable tracer of the molecular gas in high-redshift quiescent galaxies. As a consequence, we may know much less about the cold gas contents of this population than previously thought.