Quiescent Galaxies Research Articles

Radio-AGN activity across the galaxy population: dependence on stellar mass, star-formation rate, and redshift

Abstract We characterise the co-evolution of radio-loud AGN and their galaxies by mapping the dependence of radio-loud AGN activity on stellar mass and star-formation rate (SFR) across cosmic time (out to z ∼ 1.5). Deep LOFAR radio observations are combined with large galaxy samples to study the incidence of radio-loud AGN across the galaxy population; the AGN are further split into low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs). We find that LERG activity occurs over a wide range of SFRs, whereas HERGs are typically found in galaxies with ongoing star formation. The LERGs are then split based on their SFRs relative to the main sequence, across redshift. Within quiescent galaxies, LERG activity shows a steep stellar mass dependence with the same normalisation across the past ∼ 10 Gyr; this indicates that hot gas fuels LERGs in quiescent galaxies across cosmic time. In massive galaxies ($\log _{10}(M/\rm {{\rm M}_{\odot }}) \gtrsim 11$), the incidence of LERGs is roughly constant across the galaxy population, suggesting that LERGs in massive galaxies may be fuelled by hot gas regardless of the star-formation activity. At lower masses, however, LERG activity is significantly more enhanced (by a factor of up to 10) in star-forming galaxies compared to quiescent galaxies; this suggests that an additional fuelling mechanism, likely associated with cold gas, may fuel the LERGs in galaxies with higher SFRs. We find that HERGs typically accrete above 1percnt of the Eddington-scaled accretion rate, and the LERGs typically accrete below this level.

DESI Massive Poststarburst Galaxies at z ∼ 1.2 Have Compact Structures and Dense Cores

Poststarburst galaxies (PSBs) are young quiescent galaxies that have recently experienced a rapid decrease in star formation, allowing us to probe the fast-quenching period of galaxy evolution. In this work, we obtained Hubble Space Telescope (HST)/WFC3 F110W imaging to measure the sizes of 171 massive ( log(M*/M⊙)∼11) spectroscopically identified PSBs at 1 < z 1.3 selected from the DESI Survey Validation luminous red galaxy sample. This statistical sample constitutes an order of magnitude increase from the ∼20 PSBs with space-based imaging and deep spectroscopy. We perform structural fitting of the target galaxies with pysersic and compare them to quiescent and star-forming galaxies in the 3D-HST survey. We find that these PSBs are more compact than the general population of quiescent galaxies, lying systematically ∼0.1 dex below the established size–mass relation. However, their central surface mass densities are similar to those of their quiescent counterparts ( log(Σ1kpc/(M⊙kpc−2))∼10.1 ). These findings are easily reconciled by later ex situ growth via minor mergers or a slight progenitor bias. These PSBs are round in projection (b/a median ∼ 0.8), suggesting that they are primarily spheroids, not disks, in 3D. We find no correlation between the time since quenching and light-weighted PSB sizes or central densities. This disfavors apparent structural growth due to the fading of centralized starbursts in this galaxy population. Instead, we posit that the fast quenching of massive galaxies at this epoch occurs preferentially in galaxies with preexisting compact structures.

Subrelativistic Outflow and Hours-timescale Large-amplitude X-Ray Dips during Super-Eddington Accretion onto a Low-mass Massive Black Hole in the Tidal Disruption Event AT2022lri

We present the tidal disruption event (TDE) AT2022lri, hosted in a nearby (≈144 Mpc) quiescent galaxy with a low-mass massive black hole (104 M ⊙ < M BH < 106 M ⊙). AT2022lri belongs to the TDE-H+He subtype. More than 1 Ms of X-ray data were collected with NICER, Swift, and XMM-Newton from 187 to 672 days after peak. The X-ray luminosity gradually declined from 1.5 × 1044 erg s−1 to 1.5 × 1043 erg s−1 and remains much above the UV and optical luminosity, consistent with a super-Eddington accretion flow viewed face-on. Sporadic strong X-ray dips atop a long-term decline are observed, with a variability timescale of ≈0.5 hr–1 days and amplitude of ≈2–8. When fitted with simple continuum models, the X-ray spectrum is dominated by a thermal disk component with inner temperature going from ∼146 to ∼86 eV. However, there are residual features that peak around 1 keV, which, in some cases, cannot be reproduced by a single broad emission line. We analyzed a subset of time-resolved spectra with two physically motivated models describing a scenario either where ionized absorbers contribute extra absorption and emission lines or where disk reflection plays an important role. Both models provide good and statistically comparable fits, show that the X-ray dips are correlated with drops in the inner disk temperature, and require the existence of subrelativistic (0.1–0.3c) ionized outflows. We propose that the disk temperature fluctuation stems from episodic drops of the mass accretion rate triggered by magnetic instabilities or/and wobbling of the inner accretion disk along the black hole’s spin axis.

Widespread Rapid Quenching at Cosmic Noon Revealed by JWST Deep Spectroscopy

Massive quiescent galaxies in the young Universe are expected to be quenched rapidly, but it is unclear whether they all experience starbursts before quenching and what physical mechanism drives rapid quenching. We study 14 massive quiescent galaxies ( log(M⋆/M⊙)>10 ) at z ∼ 2 selected from a representative sample of the Blue Jay survey. We reconstruct their star formation histories (SFHs) by fitting spectral energy distribution models to the JWST/NIRSpec R ∼ 1000 spectra. We find that massive quiescent galaxies can be split into three categories with roughly equal numbers of galaxies according to their SFHs: (1) relatively old galaxies quenched at early epochs; (2) galaxies that are rapidly and recently quenched after a flat or bursty formation history (depending on the assumed prior); and (3) galaxies that are rapidly and recently quenched after a major starburst. Most recently quenched galaxies show neutral gas outflows, probed by blueshifted Na i D absorption, and ionized gas emission, with line ratios consistent with active galactic nucleus (AGN) diagnostics. This suggests that AGN activity drives multiphase gas outflows, leading to rapid quenching. By tracing back the SFHs of the entire sample, we predict the number density of massive quiescent galaxies at z = 4–6: n = (1.5–6.0) × 10−5 Mpc−3. The two old massive quiescent galaxies in our sample appear to have extremely early formation and quenching (z ≳ 6) and are possibly descendants of early post-starbursts at z > 3. These galaxies still show neutral gas reservoirs and weak Hα emission, perhaps because the ejective AGN feedback that caused rapid quenching has weakened over time.

Silencing the Giant: Evidence of Active Galactic Nucleus Feedback and Quenching in a Little Red Dot at z = 4.13

The James Webb Space Telescope (JWST) has uncovered a ubiquitous population of dust-obscured compact sources at z ≳ 4. Many of these objects exhibit signs of active galactic nucleus (AGN) activity, making their study crucial for understanding the formation of supermassive black holes (SMBHs) and their growth with host galaxies. In this work, we examine low and medium-resolution JWST/NIRSpec spectra from the JADES GTO public data release in the GOODS-N field of a red, luminous (M B ∼ −22.2 mag) and compact (<500 pc) source at z = 4.13. The rest-optical (λ rest > 4000 Å) continuum of this source is strongly dominated by a massive (log10[M */M ⊙] ∼ 10.6), quenched (log10[sSFR/yr−1] < −11) galaxy, as indicated by the clear presence of a Balmer break and stellar absorption lines. Star formation history modeling reveals a starburst episode followed by rapid quenching about 200 Myr ago. The spectrum shows extremely broad (FWHM ∼2500 km s−1) Hα emission and elevated optical line ratios, indicating an actively accreting SMBH. Moreover, our work has potentially revealed clear AGN signatures in the rest-UV in little red dots for the first time via the detection of a strong Lyα emission and a broad Mg ii doublet. The derived black hole mass of log10(M BH/M ⊙) ∼ 7.3 results in M BH/M * ∼ 0.04%, consistent with the local relations, unlike the elevated ratios in other high-z reddened AGN. Finally, we use JWST data from AGN at z = 4–10 to explore an evolutionary link between high-z reddened AGN, early quiescent galaxies, and local ellipticals.

Hedgehog: An Isolated Quiescent Dwarf Galaxy at 2.4 Mpc

It is well known that almost all isolated dwarf galaxies are actively forming stars. We report the discovery of dw1322m2053 (nicknamed Hedgehog), an isolated quiescent dwarf galaxy at a distance of 2.40 ± 0.15 Mpc with a stellar mass of M ⋆ ≈ 105.8 M ⊙. The distance is measured using surface brightness fluctuations with both Legacy Surveys and deep Magellan/IMACS imaging data. Hedgehog is 1.7 Mpc from the nearest galaxy group, Centaurus A, and has no neighboring galaxies within 1 Mpc, making it one of the most isolated quiescent dwarf galaxies at this stellar mass. It has a red optical color and early-type morphology and shows no UV emission. This indicates that Hedgehog has an old stellar population and no ongoing star formation. Compared with other quiescent dwarfs in the Local Group and Local Volume, Hedgehog appears smaller in size for its luminosity but is consistent with the mass–size relations. Hedgehog might be a backsplash galaxy from the Centaurus A group, but it could also have been quenched in the field by ram pressure stripping in the cosmic web, reionization, or internal processes such as supernova and stellar feedback. Future observations are needed to fully unveil its formation, history, and quenching mechanisms.

To High Redshift and Low Mass: Exploring the Emergence of Quenched Galaxies and Their Environments at 3 < z < 6 in the Ultra-deep JADES MIRI F770W Parallel

We present the robust selection of high-redshift quiescent galaxies (QG) and poststarburst (PSB) galaxies using ultra-deep NIRCam and MIRI imaging from the JWST Advanced Deep Extragalactic Survey (JADES). At 3 < z < 6, MIRI 7.7 μm imaging provides rest-frame J band, which is commonly used to break the degeneracy between old stellar populations and dust attenuation at lower redshifts. We identify 23 passively evolving galaxies in UVJ color space in a mass-limited (log M ⋆/M ⊙ ≥ 8.5) sample over 8.8 arcmin2. An evaluation of the contribution of the 7.7 μm shows that JADES-like NIRCam coverage (9+ photometric bands) can compensate for lacking the J band at these redshifts; however, more limited three-band selections perform better with MIRI. Our sample is characterized by rapid quenching timescales (∼100–600 Myr) with formation redshifts z f ≲ 9 and includes a potential record-holding massive QG at zphot=5.33−0.17+0.16 and two QGs with evidence for significant residual dust content (A V ∼ 1–2). In addition, we present a large sample of 12 log M ⋆/M ⊙ = 8.5–9.5 PSBs, demonstrating that UVJ selection can be extended to low mass. An analysis of the environment of our sample reveals that the group known as the Cosmic Rose contains a massive QG and a dust-obscured star-forming galaxy (a so-called Jekyll and Hyde pair) plus three additional QGs within ∼20 kpc. Moreover, the Cosmic Rose is part of a larger overdensity at z ∼ 3.7, which contains 7/12 of our low-mass PSBs. Another four low-mass PSBs are members of an overdensity at z ∼ 3.4; this result strongly indicates low-mass PSBs are preferentially associated with overdense environments at z > 3.

The supermassive black hole merger-driven evolution of high-redshift red nuggets into present-day cored early-type galaxies

ABSTRACT Very compact ($R_\mathrm{e}\lesssim 1$ kpc) massive quiescent galaxies (red nuggets) are more abundant in the high-redshift Universe ($z\sim 2$–3) than today. Their size evolution can be explained by collisionless dynamical processes in galaxy mergers which, however, fail to reproduce the diffuse low-density central cores in the local massive early-type galaxies (ETGs). We use sequences of major and minor merger N-body simulations starting with compact spherical and disc-like progenitor models to investigate the impact of supermassive black holes (SMBHs) on the evolution of the galaxies. With the ketju code we accurately follow the collisional interaction of the SMBHs with the nearby stellar population and the collisionless evolution of the galaxies and their dark matter haloes. We show that only models including SMBHs can simultaneously explain the formation of low-density cores up to sizes of $R_\mathrm{b} \sim 1.3$ kpc with mass deficits in the observed range and the rapid half-mass size evolution. In addition, the orbital structure in the core region (tangentially biased orbits) is consistent with observation-based results for local cored ETGs. The displacement of stars by the SMBHs boost the half-mass size evolution by up to a factor of 2 and even fast rotating progenitors (compact quiescent discs) lose their rotational support after 6–8 mergers. We conclude that the presence of SMBHs is required for merger-driven evolution models of high-redshift red nuggets into local ETGs.

Detection of strong spectral features from asymptotic-giant-branch stars in distant quiescent galaxies

Detection of strong spectral features from asymptotic-giant-branch stars in distant quiescent galaxies

Strong spectral features from asymptotic giant branch stars in distant quiescent galaxies

Strong spectral features from asymptotic giant branch stars in distant quiescent galaxies

Deciphering the properties of UV upturn galaxies in the Virgo cluster

Abstract The UV upturn refers to the increase in UV flux at wavelengths shorter than 3000 Å observed in quiescent early-type galaxies (ETGs), which still remains a puzzle. In this study, we aim to identify ETGs showing the UV upturn phenomenon within the Virgo galaxy cluster. We utilized a color-color diagram to identify all potential possible UV upturn galaxies. The Spectral Energy Distributions (SED) of these galaxies were then analyzed using the CIGALE software; we confirmed the presence of UV upturn in galaxies within the Virgo cluster. We found that the SED fitting method is the best tool to visualize and confirm the UV upturn phenomenon in ETGs. Our findings reveal that the population distributions regarding stellar mass and star formation rate properties are similar between UV upturn and red sequence galaxies. We suggest that the UV contribution originates from old stellar populations and can be modeled effectively without a burst model. Moreover, by estimating the temperature of the stellar population responsible for the UV emission, we determined it to be 13,000 K to 18,000 K. These temperature estimates support the notion that the UV upturn likely arises from the contribution of low mass evolved stellar populations (extreme horizontal branch stars). Furthermore, the Mg2 index, a metallicity indicator, in the confirmed upturn galaxies shows higher strength and follows a similar trend to previous studies. This study sheds light on the nature of UV upturn galaxies within the Virgo cluster and provides evidence that low-mass evolved stellar populations are the possible mechanisms driving the UV upturn phenomenon.

On the origin of star formation quenching in massive galaxies at ≳ in the cosmological simulations IllustrisTNG

ABSTRACT Using the cosmological simulations IllustrisTNG, we perform a comprehensive analysis of quiescent, massive galaxies at $z \gtrsim 3$. The goal is to understand what suppresses their star formation so early in cosmic time, and how other similar mass galaxies remain highly star forming. As a first-order result, the simulations are able to produce massive, quiescent galaxies in this high-redshift regime. We find that active galactic nucleus (AGN) feedback is the primary cause of halting star formation in early, massive galaxies. Not only do the central, supermassive black holes (SMBHs) of the quenched galaxies have earlier seed times, but they also grow faster than in star-forming galaxies. As a result, the quenched galaxies are exposed to AGN feedback for longer, and experience the kinetic, jet mode of the AGN feedback earlier than the star-forming galaxies. The release of kinetic energy reduces inflows of gas while likely maintaining outflows, which keeps a low cold gas fraction and decreases the star formation of the galaxies down to a state of quiescence. In addition to AGN feedback, we also investigate the influence of the large-scale environment. While mergers do not play a significant role in the quenching process, the quenched galaxies tend to reside in more massive haloes and denser regions during their evolution. As this provides a greater initial amount of infalling gas to the galaxies, the large-scale environment can mildly affect the fate of the central SMBH growth and, via AGN feedback, contribute to star formation quenching.

JWST/NIRSpec spectroscopy of intermediate-mass quiescent galaxies at z ~ 3-4

ABSTRACT We present the analysis of three intermediate-mass quiescent galaxies (QGs) with stellar masses of ${\sim} 10^{10}\, \mathrm{M}_{\odot }$ at redshifts $z\sim 3\!-\!4$ using NIRSpec low-resolution spectroscopy. Utilizing the spectral energy distribution fitting code bagpipes, we confirm these target galaxies are consistent with quiescent population, with their specific star formation rates falling below 2 dex the star-forming main sequence at the same redshifts. Additionally, we identify these QGs to be less massive than those discovered in previous works, particularly prior to the JWST era. Two of our target galaxies exhibit the potentially blended $\mathrm{ H} \, {\alpha }$ + [N ii] emission line within their spectra with signal-to-noise ratio ${\gt} 5$. We discuss whether this feature comes from an active galactic nucleus (AGN) or star formation, although future high-resolution spectroscopy is required to reach a conclusion. One of the target galaxies is covered by JWST/NIRCam imaging of the Public Release IMaging for Extragalactic Research survey. Using the 2D profile fitting code galfit, we examine its morphology, revealing a disc-like profile with a Sérsic index of $n=1.1 \pm 0.1$. On the size–mass relation, we find a potential distinction between less massive ($\log _{10}{(M_*/\mathrm{M}_\odot)}\lt 10.3$) and massive ($\log _{10}{(M_*/\mathrm{M}_\odot)}\gt 10.3$) QGs in their evolutionary pathways. The derived quenching time-scales for our targets are less than $1 \, {\rm Gyr}$. This may result from these galaxies being quenched by AGN feedback, supporting the AGN scenario of the emission line features.

Retrieval of the physical parameters of galaxies from WEAVE-StePS-like data using machine learning

Context. The William Herschel Telescope Enhanced Area Velocity Explorer (WEAVE) is a new, massively multiplexing spectrograph that allows us to collect about one thousand spectra over a 3 square degree field in one observation. The WEAVE Stellar Population Survey (WEAVE-StePS) in the next 5 years will exploit this new instrument to obtain high-S/N spectra for a magnitude-limited (IAB = 20.5) sample of ∼25 000 galaxies at moderate redshifts (z ≥ 0.3), providing insights into galaxy evolution in this as yet unexplored redshift range. Aims. We aim to test novel techniques for retrieving the key physical parameters of galaxies from WEAVE-StePS spectra using both photometric and spectroscopic (spectral indices) information for a range of noise levels and redshift values. Methods. We simulated ∼105 000 galaxy spectra assuming star formation histories with an exponentially declining star formation rate, covering a wide range of ages, stellar metallicities, specific star formation rates (sSFRs), and dust extinction values. We considered three redshifts (i.e. z = 0.3, 0.55, and 0.7), covering the redshift range that WEAVE-StePS will observe. We then evaluated the ability of the random forest and K-nearest neighbour algorithms to correctly predict the average age, metallicity, sSFR, dust attenuation, and time since the bulk of formation, assuming no measurement errors. We also checked how much the predictive ability deteriorates for different noise levels, with S/NI,obs = 10, 20, and 30, and at different redshifts. Finally, the retrieved sSFR was used to classify galaxies as part of the blue cloud, green valley, or red sequence. Results. We find that both the random forest and K-nearest neighbour algorithms accurately estimate the mass-weighted ages, u-band-weighted ages, and metallicities with low bias. The dispersion varies from 0.08–0.16 dex for age and 0.11–0.25 dex for metallicity, depending on the redshift and noise level. For dust attenuation, we find a similarly low bias and dispersion. For the sSFR, we find a very good constraining power for star-forming galaxies, log sSFR ≳ −11, where the bias is ∼0.01 dex and the dispersion is ∼0.10 dex. However, for more quiescent galaxies, with log sSFR ≲ −11, we find a higher bias, ranging from 0.61 to 0.86 dex, and a higher dispersion, ∼0.4 dex, depending on the noise level and redshift. In general, we find that the random forest algorithm outperforms the K-nearest neighbours. Finally, we find that the classification of galaxies as members of the green valley is successful across the different redshifts and S/Ns. Conclusions. We demonstrate that machine learning algorithms can accurately estimate the physical parameters of simulated galaxies for a WEAVE-StePS-like dataset, even at relatively low S/NI, obs = 10 per Å spectra with available ancillary photometric information. A more traditional approach, Bayesian inference, yields comparable results. The main advantage of using a machine learning algorithm is that, once trained, it requires considerably less time than other methods.

UNCOVER NIRSpec/PRISM Spectroscopy Unveils Evidence of Early Core Formation in a Massive, Centrally Dusty Quiescent Galaxy at z spec = 3.97

We report the spectroscopic confirmation of a massive ( log(M⋆/M⊙)=10.34±0.070.06 ), Hubble Space Telescope–dark (m F150W − m F444W = 3.6) quiescent galaxy at z spec = 3.97 in the UNCOVER survey. NIRSpec/PRISM spectroscopy and a nondetection in deep Atacama Large Millimeter/submillimeter Array imaging surprisingly reveals that the galaxy is consistent with a low (<10 M ⊙ yr−1) star formation rate (SFR) despite evidence for moderate dust attenuation. The F444W image is well modeled with a two-component Sérsic fit that favors a compact, r e ∼ 200 pc, n ∼ 2.9 component and a more extended, r e ∼ 1.6 kpc, n ∼ 1.7 component. The galaxy exhibits strong color gradients: the inner regions are significantly redder than the outskirts. Spectral energy distribution models that reproduce both the red colors and low SFR in the center of UNCOVER 18407 require both significant (A v ∼ 1.4 mag) dust attenuation and a stellar mass-weighted age of 900 Myr, implying 50% of the stars in the core already formed by z = 7.5. Using spatially resolved annular mass-to-light measurements enabled by the galaxy’s moderate magnification ( μ=2.12±0.010.05 ) to reconstruct a radial mass profile from the best-fitting two-component Sérsic model, we infer a total mass-weighted reff=0.74±0.170.22 kpc and log (Σ1kpc[M⊙kpc-2])=9.65±0.150.12 . The early formation of a dense, low SFR, and dusty core embedded in a less attenuated stellar envelope suggests an evolutionary link between the earliest-forming massive galaxies and their elliptical descendants. Furthermore, the disparity between the global, integrated dust properties and the spatially resolved gradients highlights the importance of accounting for radially varying stellar populations when characterizing the early growth of galaxy structure.

Exploring the Origin of Cold Gas and Star Formation in a Rare Population of Strongly Bulge-dominated Early-type Galaxies

We analyze the properties of a rare population, the strongly bulge-dominated early-type galaxies (sBDEs) with significant H i gas, using the databases from the FAST All Sky H i survey (FASHI) and the Arecibo Legacy Fast ALFA (ALFALFA) survey. We select the sBDEs from the Sloan Digital Sky Survey and crossmatch with the FASHI-ALFALFA combined H i sample, resulting in 104 H i-rich sBDEs. These sBDEs tend to have extremely high H i reservoirs, which is rare in previous studies such as ATLAS3D. A total of 70% of the selected sBDEs are classified as quiescent galaxies, even though they have a large H i reservoir. We study the properties of these sBDEs from four main aspects: stellar population, gas-phase metallicity, stacked H i spectra, and environment. The majority of H i-rich sBDEs appear to show lower gas-phase metallicity and are located in significantly lower-density environments, suggesting an external origin for their H i gas. We find that star-forming sBDEs exhibit statistically higher star formation efficiency and slightly older stellar populations compared to normal star-forming galaxies, suggesting a recent star formation on the Gyr timescale. They also show narrower and more concentrated H i profiles compared to control star-forming galaxies, which may explain their higher star formation efficiency.

A new perspective on the stellar mass-metallicity relation of quiescent galaxies from the LEGA-C survey

We investigated the stellar mass-metallicity relation (MZR) using a sample of 637 quiescent galaxies with 10.4 ≤ log(M*/M⊙) &lt; 11.7 selected from the LEGA-C survey at 0.6 ≤ z ≤ 1. We derived mass-weighted stellar metallicities using full-spectral fitting. We find that while lower-mass galaxies are both metal-rich and metal-poor, there are no metal-poor galaxies at high masses, and that metallicity is bounded at low values by a mass-dependent lower limit. This lower limit increases with mass, empirically defining a MEtallicity-Mass Exclusion (MEME) zone. We find that the spectral index MgFe ≡ √Mgb × Fe4383, a proxy for the stellar metallicity, also shows a mass-dependent lower limit resembling the MEME relation. Crucially, MgFe is independent of stellar population models and fitting methods. By constructing the metallicity enrichment histories, we find that, after the first gigayear, the star formation history of galaxies has a mild impact on the observed metallicity distribution. Finally, from the average formation times, we find that galaxies populate differently the metallicity-mass plane at different cosmic times, and that the MEME limit is recovered by galaxies that formed at z ≥ 3. Our work suggests that the stellar metallicity of quiescent galaxies is bounded by a lower limit which increases with the stellar mass. On the other hand, low-mass galaxies can have metallicities as high as galaxies ∼1 dex more massive. This suggests that, at log(M*/M⊙)≥10.4, rather than lower-mass galaxies being systematically less metallic, the observed MZR might be a consequence of the lack of massive metal-poor galaxies.

JWST Reveals Bulge-dominated Star-forming Galaxies at Cosmic Noon

Hubble Space Telescope imaging shows that most star-forming galaxies at cosmic noon—the peak of cosmic star formation history—appear disk-dominated, leaving the origin of the dense cores in their quiescent descendants unclear. With the James Webb Space Telescope’s high-resolution imaging to 5 μm, we can now map the rest-frame near-infrared emission, a much closer proxy for stellar mass distribution, in these massive galaxies. We selected 70 star-forming galaxies with 10 < log(M) < 12 and 1.5 < z < 3 in the CEERS survey and compare their morphologies in the rest-frame optical to those in the rest-frame near-IR. While the bulk of these galaxies are disk-dominated in 1.5 μm (rest-frame optical) imaging, they appear more bulge-dominated at 4.4 μm (rest-frame near-infrared). Our analysis reveals that in massive star-forming galaxies at z ∼ 2, the radial surface brightness profiles steepen significantly, from a slope of ∼0.3 dex−1 at 1.5 μm to ∼1.4 dex−1 at 4.4 μm within radii <1 kpc. Additionally, we find their total flux contained within the central 1 kpc is approximately 7 times higher in F444W than in F150W. In rest-optical emission, a galaxy’s central surface density appears to be the strongest indicator of whether it is quenched or star-forming. Our most significant finding is that at redder wavelengths, the central surface density ratio between quiescent and star-forming galaxies dramatically decreases from ∼10 to ∼1. This suggests the high central densities associated with galaxy quenching are already in place during the star-forming phase, imposing new constraints on the transition from star formation to quiescence.

The Velocity Dispersion Function for Quiescent Galaxies in Massive Clusters from IllustrisTNG

We derive the central stellar velocity dispersion function (VDF) for quiescent galaxies in 280 massive clusters with log(M200/M⊙)>14 in IllustrisTNG300. The VDF is an independent tracer of the dark matter mass distribution of subhalos in galaxy clusters. Based on the IllustrisTNG cluster catalog, we select quiescent member subhalos with a specific star formation rate <2 × 10−11 yr−1 and stellar mass log(M*/M⊙)>9 . We then simulate fiber spectroscopy to measure the stellar velocity dispersion of the simulated galaxies; we compute the line-of-sight velocity dispersions of star particles within a cylindrical volume that penetrates the core of each subhalo. We construct the VDFs for quiescent subhalos within R 200. The simulated cluster VDF exceeds the simulated field VDF for logσ*>2.2 , indicating the preferential formation of large velocity dispersion galaxies in dense environments. The excess is similar in simulations and in the observations. We also compare the simulated VDF for the three most massive clusters with log(M200/M⊙)>15 with the observed VDF for the two most massive clusters in the local Universe, Coma and A2029. Intriguingly, the simulated VDFs are significantly lower for logσ*>2.0 . This discrepancy results from (1) a smaller number of subhalos with log(M*/M⊙)>10 in TNG300 compared to the observed clusters, and (2) a significant offset between the observed and simulated M *–σ * relations. The consistency in the overall shape of the observed and simulated VDFs offers a unique window into galaxy and structure formation in simulations.

The JWST-SUSPENSE Ultradeep Spectroscopic Program: Survey Overview and Star Formation Histories of Quiescent Galaxies at 1 < z < 3

We present an overview and first results from the Spectroscopic Ultradeep Survey Probing Extragalactic Near-infrared Stellar Emission (SUSPENSE), executed with NIRSpec on JWST. The primary goal of the SUSPENSE program is to characterize the stellar, chemical, and kinematic properties of massive quiescent galaxies at cosmic noon. In a single deep NIRSpec/MSA configuration, we target 20 distant quiescent galaxy candidates (z = 1–3, H AB ≤ 23), as well as 53 star-forming galaxies at z = 1–4. With 16 hr of integration and the G140M-F100LP dispersion-filter combination, we observe numerous Balmer and metal absorption lines for all quiescent candidates. We derive stellar masses (logM */M ⊙ ∼ 10.2–11.5) and detailed star formation histories (SFHs) and show that all 20 candidate quiescent galaxies indeed have quenched stellar populations. These galaxies show a variety of mass-weighted ages (0.8–3.3 Gyr) and star formation timescales (∼0.5–4 Gyr), and four out of 20 galaxies were already quiescent by z = 3. On average, the z > 1.75 [z < 1.75] galaxies formed 50% of their stellar mass before z = 4 [z = 3]. Furthermore, the typical SFHs of the galaxies in these two redshift bins (z mean = 2.2 [1.3]) indicate that galaxies at higher redshift formed earlier and over shorter star formation timescales compared to lower redshifts. Although this evolution is naturally explained by the growth of the quiescent galaxy population over cosmic time, number density calculations imply that mergers and/or late-time star formation also contribute to the evolution. In future work, we will further unravel the early formation, quenching, and late-time evolution of these galaxies by extending this work with studies on their chemical abundances, resolved stellar populations, and kinematics.