The mid-infrared (mid-IR) spectrum in galaxies has a long history as a valuable proxy for the dust-obscured component of the star formation rate (SFR) in massive galaxies. In this work, we exploit the capabilities of the James Webb Space Telescopes (JWST) to expand our understanding of the mid-IR and its use in measuring SFRs, covering four orders of magnitude in total infrared luminosity (9≲ log L_ IR/L_⊙≲13). First, using a Main Sequence sample at 1<z<1.75 from SMILES, we calibrate mid-IR-based SFRs against the P_ aα emission line - a gold standard SFR indicator - from the FRESCO survey. We find that the rest-frame ∼6-8 μm emission - dominated by PAHs and probed by the Mid-Infrared Instrument (MIRI) at z∼1.3 - has a superlinear relation with SFR_ P_aα below ∼8 M_⊙ yr^-1, in sharp contrast with the unity relation in more massive galaxies. We derive SFR calibrations for MIRI photometry, finding that a single, representative IR template improves the scatter. We additionally calibrate a UV+IR composite indicator, assuming energy balance, which does return a unity relation, with low scatter. Our examination of the mid-IR in our MS sample indicates that it is tracking the global obscuration fraction, making it a robust proxy for SFR down to our low mass end, log M_⋆/M_⊙∼9, and across the redshift range where MIRI probes the PAHs (0.3≲ z≲3). Finally, we examine the bright end not represented in SMILES, comparing the behavior of local and cosmic noon ultra luminous infrared galaxies to show that the robustness of using the IR as a SFR proxy extends from the faint to bright regimes.

We compile JWST/NIRSpec prism and MIRI data for 249 Little Red Dots (LRDs) at 2.3<z<9.3, forming a representative spectroscopic subset of NIRCam-selected LRDs. We derive a median stacked spectrum covering rest-frame 0.09-1.2 μm, with MIRI photometry extending the spectral energy distribution to 4 μm. Four additional stacks for subsamples defined by optical-to-UV luminosity ratios show that LRDs form a heterogeneous population spanning diverse continuum slopes and line properties. Assuming LRDs host super-massive black holes (BHs) surrounded by dense gas clouds, and stars accompany this core, we infer masses of M_BH∼10^6.0-6.5 M_⊙ and M_∼10^8.3 M_⊙, corresponding to BH-to-stellar mass ratios of 1-2

We present a photometric analysis of globular clusters (GCs) in the massive galaxy cluster MACS J0416.1−2403 ( z = 0.397) using deep JWST/NIRCam imaging from the PEARLS program. Point-spread function photometry was performed in the short wavelength filters, F090W, F115W, F150W, and F200W, yielding a catalog of ∼3 × 10 ^3 unresolved, point-like sources consistent with a GC population. Artificial-star tests indicate 80% completeness at F200W ≃ 30.36 mag. The color–magnitude diagrams show a narrow GC sequence well reproduced by PARSEC single-stellar-population models spanning ages of 5–9 Gyr and metallicities from [M/H] ≈ −2.0 to +0.2, consistent with evolved GC systems at this redshift. The GC luminosity function follows a log-normal form truncated by incompleteness at the faint end. The brightest sources extend slightly beyond the locus of classical GCs, suggesting a small number of ultracompact dwarf-like systems or stripped nuclei, while the bulk of the population exhibits the luminosities and colors expected for mature GCs at z ≃ 0.4.

Our understanding of the physical properties of star-forming galaxies during the Epoch of Reionization (EoR; at z > 6) suffers from degeneracies among the apparent properties of the stars, nebular gas, and dust. These degeneracies are most prominent with photometry, which has insufficient (1) spectral resolution and (2) rest-frame spectral coverage. We explore ways to break these degeneracies with a sample of N = 22 high-redshift star-forming galaxies at 7 < z(phot) <= 9, using some of the deepest existing imaging from JWST/NIRCam and JWST/MIRI with JADES. Key to this study is the imaging from JWST/MIRI at 7.7 mu m, which provides coverage of the rest-frame I band at the observed redshifts. We infer stellar population properties and rest-frame colors using a variety of filter sets and star formation history (SFH) assumptions to explore the impact of these choices. Evaluating these quantities both with and without the 7.7 mu m data point shows that dense spectral coverage with JWST/NIRCam (eight or more filters, including at least one medium-band at lambda(obs) approximate to 4-5 mu m) can compensate for lacking the rest-frame I-band coverage for the vast majority (approximate to 80%) of our sample. Furthermore, these galaxy properties are most consistently determined by assuming the delayed-tau SFH, which provides the smallest offsets and scatters around these offsets when including JWST/MIRI. Within extragalactic surveys like JADES and CEERS, our findings suggest that robust characterization of the stellar population properties and rest-frame colors for typical high-redshift star-forming galaxies (i.e., galaxies with M-UV approximate to -20 and beta(UV) approximate to -2) is possible with JWST/NIRCam alone at z approximate to 8.

ABSTRACT The discovery of high-redshift galaxies exhibiting a steep spectral ultraviolet (UV) downturn potentially indicative of two-photon continuum emission marks a turning point in our search for signatures of star formation following a top-heavy initial mass function in the early Universe. We develop a photometric search method for identifying further nebular-dominated galaxy candidates, whose nebular continuum dominates over the starlight, due to the high ionizing photon production efficiencies $\xi _\mathrm{ion}$ associated with massive star formation. We utilize the extensive medium-band imaging from the JWST Advanced Deep Extragalactic Survey (JADES), which enables the identification of Balmer jumps across a wide range of redshifts ($1.5 \lt z \lt 8.5$), through the deficit in rest-frame optical continuum level. As Balmer jumps are a general recombination feature of young starbursts ($\lesssim 3$ Myr), we further demand a high observed $\log \, (\xi _\mathrm{ion, obs}/\mathrm{(Hz\ erg^{-1})}) \gt 25.60$ to power the strong nebular continuum, together with a relatively non-blue UV slope ($m_\mathrm{F115W}-m_\mathrm{F200W} \gt -0.4$ at $z=6$) indicating a lack of stellar continuum emission. Our nebular-dominated candidates, constituting ${\sim }11$ per cent of galaxies at $z \sim 6$ (decreasing to ${\sim }2$ per cent at $z \sim 2$, not completeness-corrected) are faint in the rest-frame optical (median $M_\mathrm{opt} = -17.95$) with extreme line emission (median $\mathrm{EW}_\mathrm{H\alpha , rest} = 1567$ Å, $\mathrm{EW}_\mathrm{[O\ III] + H\beta ,rest} = 2292$ Å). However, hot H ii region temperatures, collisionally enhanced two-photon continuum emission, and strong UV lines are expected to accompany top-heavy star formation. Thus nebular-dominated galaxies do not necessarily exhibit the biggest Balmer jumps, nor the largest $\xi _\mathrm{ion, obs}$ or reddest UV slopes. Hence continuum spectroscopy is ultimately required to establish the presence of a two-photon downturn in our candidates, thus advancing our understanding of primordial star formation and active galactic nucleus.

mediawiki-texvcGalaxy assembly was already well underway in the first 400 Myr of cosmic time, as recently revealed by JWST. However, the contribution of these early galaxies to cosmic reionisation remains uncertain. Here we present new JWST/NIRSpec observations of GS-z13-1-LA obtained as part of the OASIS and JADES programmes, whose combined deep (56 h) NIRSpec/PRISM spectrum confirms the Lyman- line detection and blue UV continuum at redshift z = 13.1 presented in a previous work. The measured Lyman- emission (rest-frame equivalent width of 66_-9^+10 Å) and steep continuum slope (β_UV≈ -3) point towards GS-z13-1-LA hosting a remarkably hot and powerful ionising source, and allow at most a modest contribution from the nebular continuum. The steep turnover of the continuum is still present, but less pronounced in the new OASIS spectrum. Combined, this implies that ionising photons may escape GS-z13-1-LA at a sufficient rate to weaken the other, still undetected UV lines, and to lead the formation of a small ionised bubble (R_ion≈ 0.2 pMpc). A yet larger bubble could alleviate the required ionising production efficiency of GS-z13-1-LA from ξ_ion≈ 10^26.4 Hz erg^-1 down to ≈ 10^25.9 Hz erg^-1, still extremely high but more readily reconcilable with stellar models. In turn, this would require a notable overdensity of galaxies with highly efficient ionising capabilities, a scenario for which tentative evidence is found in the form of 16 nearby photometric candidates and one spectroscopically confirmed source, JADES-GS-z13-0. The new OASIS observations therefore confirm the overall picture of GS-z13-1-LA as an early beacon of reionisation, providing compelling evidence for its start only 330 Myr after the Big Bang.

The James Webb Space Telescope North Ecliptic Pole (NEP) Time-Domain Field (TDF) has been monitored by Nuclear Spectroscopic Telescope Array (NuSTAR) and XMM-Newton with a regular cadence for 5 yr, starting in 2019. The survey has accumulated 3.5 Ms of NuSTAR exposure and 228 ks quasi-simultaneous XMM-Newton observations covering 0.31 deg2. This paper presents the results from the most recent 2 years' worth of 2 Ms NuSTAR and 166 ks XMM observations in NuSTAR cycles 8 and 9. These observations reached a 20% area flux of 2.20 x 10-14 erg cm-2 s-1 in the 8-24 keV band. Note that 75 NuSTAR sources and 274 XMM-Newton sources are detected at 99% reliability level. The logN-logS measured in cycles 8+9 are consistent with those measured in the previous cycle 5+6 NuSTAR NEP survey, but in a larger area (0.3 deg2 compared with 0.19 deg2). The slope of the cycles 8+9 8-24 keV logN-logS curve is flatter than other works (alpha 89 = 1.13 +/- 0.46), but is consistent with the Euclidean value of alpha = 1.50. In addition, we found similar to 36% of the NuSTAR sources to be heavily obscured (NH >= 1023 cm-2). The Compton-thick (NH >= 1024 cm-2) active galactic nuclei fraction is 9-8+18% in the NEP-TDF, which is consistent with the measurements in previous surveys.

In Paper I, we exploited the unsurpassed resolution and depth of JWST/NIRCam imagery to investigate the relationship between active galactic nuclei (AGN) and host-galaxy properties in the JWST era, finding a correlation between the level of spatial disturbance (as measured by shape asymmetry, A _S ) and obscuration ( N _H ). Here in Paper II, we report an expansion of our X-ray and infrared analysis of Seyfert-luminosity host galaxies with four additional metrics to the single-metric morphology analysis of Paper I, as well as new samples of inactive control galaxies. This expanded study of one of the largest and most complete, multiwavelength samples of AGN detected at 0.6 < z < 3.8 in the GOODS-South and -North fields, confirms that mergers surprisingly play a significant role in obscured, subquasar AGN host galaxies. Additionally, the pattern of morphological disturbances observed amongst the X-ray- and mid-IR-selected AGN suggests that these represent different phases of AGN evolution tied to a major-merger timeline, as opposed to distinct populations of AGN. These results indicate that mergers are important in triggering subquasar AGN at these redshifts.

We present a detailed study of HUDFJ0332.4-2746.6 (HUDF46), a $z \approx 1.84$ overdensity in the Hubble Ultra Deep Field, previously identified with HST as a proto-cluster. JWST/NIRISS spectroscopy expands its confirmed membership from 18 to 37 galaxies, while deep HST/ACS, JWST/NIRCam, and JWST/MIRI imaging provide a comprehensive multiwavelength view from the rest-frame UV to the mid-infrared. This dataset probes the population across three dex in stellar mass ($M_\bigstar \approx 10^{7.5\text{--}10.5}\,M_\odot$), delivering the first direct view of a young cluster down to such low-$M_\bigstar$ at $z\gtrsim1$. Assuming virialization, we derive a velocity dispersion of $σ\approx 670\pm 91\,\mathrm{km\,s^{-1}}$ and a halo mass of $M_{200} \approx (1.2\pm0.2) \times 10^{14}\,M_\odot$, in agreement with X-ray constraints from deep {\it Chandra} data. Despite residing in a massive halo likely in the hot-halo regime, the population is overwhelmingly star-forming, with no established red sequence and no extended X-ray emission from a hot intracluster medium. HUDF46 members have stellar and structural properties nearly indistinguishable from coeval field galaxies, and the structure hosts only one AGN candidate, found in its brightest galaxy, which lies at the cluster center. Overall, HUDF46 appears to be in a transitional phase prior to the onset of environmental quenching, making its galaxy population a key benchmark for tracing the processes that will later build a passive population and shape the assembly of massive clusters at later cosmic times.

Medium to ultra-deep mid-infrared imaging surveys with the James Webb Space Telescope (JWST)'s Mid-Infrared Instrument (MIRI) are reframing our view of the early Universe, from the emergence of ultra-red dusty and quiescent galaxies to the epoch of reionization to the first galaxies. Here we present the MIRI coordinated parallels component of the JADES program, which obtained ultra-deep (155 ks) imaging at 7.7 μm over ∼10 arcmin^2 as well as medium depth (∼5-15 ks) imaging at 7.7, 12.8, and 15 μm over ∼36, 25, and 22 arcmin^2, respectively, in the GOODS-S and GOODS-N fields. This paper describes the data reduction, which combines the official JWST Calibration Pipeline with custom steps to optimize flagging of warm/hot pixels and optimize background subtraction. We further introduce a new step to address artifacts caused by persistence from saturating sources. The final, fully reduced JADES/MIRI mosaics are being released as part of JADES Data Release 5, along with prior-based forced photometry using NIRCam detection images, providing critical rest-frame near-infrared and optical constraints on early galaxy populations.

JWST is beginning to uncover a population of extremely metal-poor galaxies (EMPGs, Z < 1% Z_⊙) at z > 3, mostly through serendipitous NIRSpec discoveries and blind slitless spectroscopy. To accelerate our understanding of pristine star formation, we further develop a methodology to identify EMPG candidates from photometry, using the extensive deep medium-band imaging from JADES. Our EMPG candidates at 2.5 < z < 6.5 exhibit strong photometric boosts by Hα, yet correspondingly weak boosts by [O III] + Hβ, likely indicating extremely low metallicity to explain their lack of [O III] emission. We further demand our EMPG candidates to have strong Balmer jumps, as revealed by medium-band imaging, to ensure that they are young starbursts, as opposed to broad-line AGN/LRDs, though contamination by dusty/dense-gas starbursts and highly-obscured AGN remains a concern. SED-fitting with near-pristine models (∼0.1-1% Z_⊙) indicates that our 22 EMPG candidates are low-mass (median M_* ≈ 10^6.7 M_⊙), faint dwarf galaxies (M_UV≈ -16.6), with high ionizing photon production efficiencies (log (ξ_ion, obs/(Hz erg^-1)) ≈ 26.0). Hence these are plausible sites of near-pristine star formation, comprising ∼0.04-0.6% of 2.5 < z < 6.5 galaxies at -19 < M_UV < -16. We discuss this extremely metal-poor extension to the mass-metallicity relation. We forecast that deep (∼28 h) NIRCam slitless spectroscopy can identify bright EMPGs through strong Hβ but lack of [O III] emission, or secure the redshifts of fainter systems through Hα detections. Highly-multiplexed NIRSpec spectroscopy offers an alternate route to discovering the faintest pristine galaxies out to z=10, without requiring deep medium-band/MIRI imaging to identify secure candidates.

The initial distance to PEARLSDG estimated from the Tip of the Red Giant Branch suggested it was an exotic isolated quiescent dwarf galaxy. We combine recent and archival Hectospec spectroscopy to place it at z = 0.02843 ± 0.00012 (D ≈ 124 Mpc) within a galaxy group, revising the distance from 30 Mpc to ∼124 Mpc. We then carry out Prospector SED fitting using parametric and non-parametric star-formation histories sampled with , , and , recovering metallicity log(Z/Z_⊙) = -0.44^+0.35_-0.06, stellar mass log_10(M_*/M_⊙) = 9.25^+0.02_-3.73, and dust attenuation _V = 0.67^+0.02_-0.05. The updated metallicity places PEARLSDG squarely on the standard mass–metallicity relation, resolving its former outlier status, with its quenched star-formation history consistent with environmental quenching in a group setting.

We report the confirmation of a HeIIλ1640 emitter located at 3 pkpc from the galaxy GN-z11, at z=10.6. The detection, based on JWST NIRSpec-IFU high-resolution spectroscopy, confirms a previous claim based on medium-resolution spectroscopy. The HeIIλ1640 identification is further supported by the independent detection of Hγ obtained by Übler et al. (2026) at the same location. The HeII emission is spectrally resolved in two components separated by 120 km/s. The Equivalent Width of the HeII emission is extremely high (>20 A). No metal lines are detected. Population III stars appear to be the most plausible explanation for the observed HeII emission. We argue that Population III stars are the most plausible explanation for the observed He II emission, with no satisfactory alternative from other classes of sources or mechanisms.

In the local Universe, supermassive black hole (SMBH) masses strongly correlate with their host-galaxies' stellar masses (M_*), but galaxies hosting faint AGN recently found by JWST may deviate from this relation. To constrain the M_BH-M_* relation at high redshift, we performed AGN-host image decomposition for 17 low-luminosity AGN galaxies at z ∼ 4–6 using NIRCam images in the JADES GOODS-N field. These sources are identified as AGNs from broad Hα emission lines detected by the CONGRESS and FRESCO surveys. We used galfit+MCMC to fit spatial profiles in 7 wide-band images and detected extended emission in 9 sources out of 17. The close spatial alignment between the extended components and the AGN centers indicates that this emission likely originates from the host galaxies. These sources are extended at 0.9–2.0 μm, suggesting significant host-galaxy light in the rest-frame UV. For the sources with the host detection, the stellar mass inferred based on image decomposition result can be 1-2 dex lower than the results without image decomposition. The BH-to-stellar mass ratio spans M_BH/M_∗ ∼ 0.01–1.48, placing them well above the local M_BH–M_∗ relation. In contrast, the host-galaxy size–mass relation broadly agrees with previous measurements. Our results suggest that the host galaxies of these faint AGN are either genuinely under-massive compared to their black hole masses, or too compact to be spatially resolved.

We present morphological parameters and their uncertainties for all sources detected in JWST/NIRCam imaging in GOODS-N and GOODS-S from the JWST Advanced Deep Extragalactic Survey (JADES) catalogs. We model the surface brightness profiles of these sources with single-component Sérsic profiles, performing Bayesian inference of galaxy structural parameters. We fit each of the >10^5 sources with every available JWST/NIRCam wide-band filter individually, amounting to over 3 million Sérsic profiles computed. We provide catalogs of this morphological information, building one of the largest extragalactic morphological datasets to date, which we share alongside imaging and photometry from the JADES Data Release 5. With this information, we analyze the rest-frame optical redshift evolution of the effective radius and the surface luminosity density within a radius of 1 kiloparsec, Σ_1 kpc, for 24,692 galaxies at z>1. We find r_eff∝ (1+z)^-0.635 ± 0.013 kpc, while Σ_1 kpc is relatively constant across time. Additionally, we explore bulge-disk decomposition on a subset of 8,390 galaxies in the JADES deep imaging covering the Hubble Ultra Deep Field, finding the effective radius of the bulge-components to increase marginally with time, whereas the disk-component sizes evolve as r_eff,disk∝ (1+z)^-1.091 ± 0.043. Future work modeling multi-component surface brightness profiles will enable further analysis of the morphological evolution of galaxies across cosmic time.

We model spectral energy distributions of 261 X-ray sources to $z \sim 5$ in the North Ecliptic Pole Time Domain Field, extending prior XMM-Newton and NuSTAR analyses. Using the star-forming main sequence (SFMS) and black hole accretion rate (BHAR) frameworks, we find that SFRs generally lie below the SFMS while most BHARs exceed the population average, as expected for X-ray-selected samples. There is a strong correlation ($ρ=+0.73$) between SFR relative to the SFMS and specific AGN luminosity, $L_{AGN}/M_*$; galaxies with the highest $L_{AGN}/M_*$ exist at or above the SFMS. X-ray luminosity correlates with SFR ($ρ=+0.80$), revealing a star-forming and X-ray luminous "cold quasar" population consistent with dramatic, short-timescale accretion episodes. Low-mass galaxies show BHARs well above the population averaged value for their mass whereas high-mass galaxies' SMBHs accrete at the population averaged BHAR, suggesting "growth spurt" and "maintenance-mode" accretion, respectively. Traditional AGN classifications (obscured, unobscured, or radio-loud) do not reveal these distinctions, demonstrating the X-ray perspective's unique ability to identify rare AGN phases that are critical for the instantaneous link between galaxies and their SMBHs.

We investigate galaxies in the Galaxies at All Redshifts Deciphered and Explained with the NIRSpec microshutter array (MSA; GARDEN) survey that exhibit auroral emission lines, enabling spatially resolved measurements of electron temperature and direct oxygen abundances. Two galaxies in this survey have spectra suitable for this analysis: CANDELS 8005 at z = 3.794 and CANDELS 7986 at z = 4.702. For both galaxies, we measure auroral and key nebular emission-line fluxes across their full extent, allowing direct-method oxygen abundance determinations in individual spatial pixels (spaxels). These observations demonstrate the viability of deep JWST/NIRSpec MSA spectroscopy for spatially resolved chemical analyses at high redshift, aided by weak nebular continua and low interstellar extinction. We derive global direct abundances of log(O/H)+12 = 8.008 (+0.025)(-0.027) for CANDELS 8005 and 7.89 (+0.027)(-0.028) for CANDELS 7986. Emission-line diagnostics indicate neither galaxy hosts an active galactic nucleus. A first-order kinematic analysis suggests a potential merger in CANDELS 8005. The direct abundances are consistent with strong-line estimates based on our data and recent high-redshift calibrations. We build emission line, radial velocity, strong-line abundance indices, electron temperature, and direct abundance maps for both galaxies, thanks to the excellent spatial resolution. From the direct abundance maps, we measure linear radial metallicity gradients of -0.111(-0.025)(+0.026 )dex kpc(-1) for CANDELS 8005 (statistically significant) and -0.0928 +/- 0.0880 dex kpc(-1) for CANDELS 7986, where the large uncertainties limit the significance of the result. These results provide a rare direct measurement of a radial metallicity gradient at z > 0 from direct-method abundances, offering key observational support for inside-out galaxy growth with feedback-regulated chemical enrichment.

We present the second data release of the Systematic Mid-Infrared Instrument Legacy Extragalactic Survey (SMILES), focusing on JWST/NIRSpec medium-resolution spectroscopy of galaxies across cosmic time. This release includes spectroscopic observations of 166 galaxies spanning 0 < z < 7.5, sampling star-forming galaxies, quiescent systems, and active galactic nuclei (AGNs), with an emphasis on galaxies at cosmic noon ( z ∼ 1–3). We describe the target selection strategy, the observational setup with the G140M/F100LP and G235M/F170LP gratings, and the data calibration process. The final data products include the reduced spectra, redshift catalog, emission-line catalogs produced with GELATO for emission-line galaxies and pPXF fits for quiescent systems, and ancillary spectral energy distribution fit results derived from multiband photometry. The SMILES NIRSpec dataset enables investigations of obscured AGNs, multiphase outflows, ionizing properties, and the role of environment in galaxy evolution. All data products are publicly available through STScI/MAST at https://archive.stsci.edu/hlsp/smiles .

Wisps are among the most prominent scattered light artifacts in JWST/NIRCam imaging. They often appear in certain regions of the detectors and contaminate observations at surface-brightness levels relevant for faint-source photometry. We introduce a new subtraction method that uses the non-negative matrix factorization (NMF) algorithm to model and remove wisps. Using deep NIRCam observations from the JWST Advanced Deep Extragalactic Survey (JADES) and other programs, we construct multi-component, filter- and detector-specific wisp templates that capture the wisp structures and their exposure-to-exposure morphological variations. Wisps in individual exposures are represented as non-negative linear combinations of these templates, consistent with their additive nature and reducing degeneracies relative to single-template scaling. Compared to existing approaches, our method delivers lower residual root mean square in wisp-affected regions and reduces photometric bias and scatter to levels consistent with clean detector areas. The NMF wisp templates are readily applicable to other datasets and are publicly released to support future NIRCam extragalactic surveys.

We present the UV-to-near-IR (NIR) size evolution of a sample of 161 quiescent galaxies with M-* > 10(10)M(circle dot)over 0.5 < z < 5. With deep multiband NIRCam images in GOODS-South from JADES, we measure the effective radii (R-e) of the galaxies at rest-frame 0.3, 0.5, and 1 mu m. On average, we find that quiescent galaxies are 45% (15%) more compact at rest-frame 1 mu m than they are at 0.3 mu m (0.5 mu m). Regardless of wavelengths, the R-e of quiescent galaxies strongly evolves with redshift, and this evolution depends on stellar mass. For lower-mass quiescent galaxies with M-* = 10(10)-10(10.6)M(circle dot), the evolution follows R-e proportional to (1 + z)(-1.1), whereas it becomes steeper, following R-e proportional to (1 + z)(-1.7), for higher-mass quiescent galaxies with M-* > 10(10.6)M(circle dot). To constrain the physical mechanisms driving the apparent size evolution, we study the relationship between R-e and the formation redshift (z(form)) of quiescent galaxies. For lower-mass quiescent galaxies, this relationship is broadly consistent with R-e proportional to(1+z(form))(-1) , in line with the expectation of the progenitor effect. For higher-mass quiescent galaxies, the relationship between R-e and z(form) depends on stellar age. Older quiescent galaxies have a steeper relationship between R-e and z(form) than that expected from the progenitor effect alone, suggesting that mergers and/or post-quenching continuous gas accretion drive additional size growth in very massive systems. We find that the z > 3 quiescent galaxies in our sample are very compact, with mass surface densities Sigma(e) greater than or similar to 10(10)M(circle dot) kpc(-2), and their R-e are possibly even smaller than anticipated from the size evolution measured for lower-redshift quiescent galaxies. Finally, we take a close look at the structure of GS-9209, one of the earliest confirmed massive quiescent galaxies at z(spec) similar to 4.7. From UV to NIR, GS-9209 becomes increasingly compact, and its light profile becomes more spheroidal, showing that the color gradient is already present in this earliest massive quiescent galaxy.