Andrea Weibel

We measure the number density and field-to-field variance of massive quiescent galaxies at z ∼ 3–8 using the JWST/NIRCam pure-parallel imaging survey PANORAMIC together with archival observations, covering an area of 0.28 deg ² (∼1000 arcmin ² ) in at least six filters. We identify quiescent galaxy candidates at z ≳ 3 with M _* ≳ 10 ¹⁰ M _⊙ , comprising 101 galaxies in a gold sample of high-confidence candidates and 137 in a more inclusive silver sample. We measure their evolving comoving number density, finding (1.5 versus 3.1) × 10 ⁻⁵ Mpc ⁻³ at z = 3–4 for the gold and silver samples, respectively, and a decline by more than a factor of 20 by z ∼ 6. Comparisons with empirical models and cosmological simulations show that widely used frameworks underpredict the abundance of massive quiescent galaxies at z ≳ 4 by ≳1 dex, indicating that current implementations of early star formation, feedback, and quenching do not produce enough early quenched systems. With 34 independent sight lines, we present the first direct empirical measurement of field-to-field variance for quiescent galaxies at z > 3, finding a high cosmic variance of σ _CV ≈ 0.7 ± 0.3. This exceeds predictions from abundance-matched mock catalogs, suggesting that early quiescent galaxies are more strongly clustered, and more likely to be found near one another or in more biased regions, than expected in current galaxy-formation models. Any successful model for the emergence of early massive quiescent galaxies must reproduce both their abundance evolution and their imprint on the large-scale distribution.

The physical processes that led to the formation of billion-solar-mass black holes within the first 700 million years of cosmic time, a period known as cosmic dawn, remain a puzzle ¹ . Several theoretical scenarios have been proposed to seed and rapidly grow black holes ^2–4 , but direct observations of these mechanisms remain elusive. Here we present a source 660 million years after the Big Bang that exhibits singular properties: among the largest hydrogen Balmer breaks reported at any redshift, broad multi-peaked Hβ emission, and Balmer line absorption in several transitions. We model this source as an enshrouded black hole in which the Balmer break and absorption features are a result of extremely dense, turbulent gas forming a dust-free envelope around a supermassive black hole ^5,6 . This source may provide evidence of an early black hole embedded in dense gas—a theoretical configuration proposed to rapidly grow black holes by super-Eddington accretion ^7,8 . Radiation from the black hole seems to dominate almost all observed light, leaving limited room for contribution from its host galaxy. If the source merged with its brighter neighbour, it would resemble the recently discovered ‘little red dots’ with perplexing spectral energy distributions ^9–11 . The redness of the black hole is due to gas, not dust ^12,13 , and scattering, not kinematics, gives rise to the complex line shapes and luminosities—black hole masses of these sources may therefore be overestimated by orders of magnitude.

The correlation between galaxy stellar mass and gas-phase metallicity, known as the mass–metallicity relation (MZR), gives key insights into the processes that govern galaxy evolution. However, unquantified observational and selection biases can result in systematic errors in attempts to recover the intrinsic MZR, particularly at higher redshifts. We characterize the MZR at z ∼ 3–6 within a fully Bayesian framework using JWST/NIRSpec spectra of 191 galaxies from the RUBIES survey. We forward model the observed mass–metallicity surface using prospector -generated spectra to account for two selection biases: the survey selection function and the success in observing high signal-to-noise ratio emission lines. We demonstrate that the RUBIES selection function, based on F444W magnitude and F150W – F444W color, has a negligible effect on our measured MZR. A correct treatment of the non-Gaussian metallicity uncertainties from strong-line calibrations lowers the derived MZR normalization by 0.2 dex and flattens the slope by ∼20%; forward modeling the effect of emission line observability steepens the slope by ∼15%. Both of these biases must be taken into account in order to properly measure the intrinsic MZR. This novel forward-modeling process motivates careful consideration of selection functions in future surveys, and paves the way for robust, high-redshift chemical enrichment studies that trace the evolution of the MZR across cosmic time.

Recent studies at high redshift have revealed an enigmatic class of little red dots (LRDs) with extreme Balmer breaks, stronger than in any stellar atmosphere. However, it is unclear whether such objects exist at lower redshift, especially given the low number of LRDs reported at z ≲ 2. Here, we report the discovery of PAN-BH*-1, an LRD with an extreme Balmer break at z = 1.73, identified from JWST/NIRCam pure-parallel imaging taken by the PANORAMIC survey, and confirmed by deep VLT/X-Shooter spectroscopy. The rest-optical to near-infrared spectral energy distribution of PAN-BH*-1 is consistent with a photospheric continuum with effective temperature T _eff ≈ 4800 K. The broad H α emission line shows remarkably deep absorption, stronger than previously measured in any LRD. The absorption trough spans from −520 to +267 km s ⁻¹ with respect to the systemic redshift. The presence of blue- and red-shifted absorption suggests complex dynamics of the obscuring gas along the line of sight. We speculate that the absorption trough can be produced by a thick wind launched from a thick, rotating photospheric disk, the latter being the source of the red optical continuum. While the source is unresolved in the rest-optical JWST data ( r _eff < 47 pc), the rest-near-UV Hubble Space Telescope imaging shows an extended morphology with r eff = 1 . 0 − 0.3 + 0.5 kpc, which we interpret as a host galaxy with a stellar mass of ∼10 ⁸ M _⊙ , in line with the narrow H α emission. The discovery of this object at cosmic noon highlights the feasibility of systematic searches for extreme LRDs with wide-area facilities such as Euclid and Roman.

Observational campaigns with JWST have revealed a higher-than-expected abundance of UV-bright galaxies at z ≳ 10, with various proposed theoretical explanations. A powerful complementary constraint to break degeneracies between different models is galaxy clustering. In this paper, we combine PANORAMIC pure parallel and legacy imaging along 34 independent sight lines to measure the cosmic variance ( σ _CV ) in the number counts of Lyman break galaxies at z ∼ 10, which is directly related to their clustering strength. We find σ CV = 0.9 6 − 0.18 + 0.20 , 1.4 6 − 0.44 + 0.54 , and 1.7 1 − 0.59 + 0.72 per NIRCam pointing ( ∼ 9.7 arcmin 2 , ≲1.5 pMpc at z ∼ 10) for galaxies with M _UV < −19.5, −20, and −20.5. Comparing to galaxies in the fiducial UniverseMachine , we find that σ _CV is consistent with our measurements, but that the number densities are a factor ≳5 lower. We implement simple models in the UniverseMachine that represent different physical mechanisms to enhance the number density of UV-bright galaxies. All models decrease σ _CV by placing galaxies at fixed M _UV in lower-mass halos, but to varying degrees. Combined constraints on σ _CV and the UV luminosity function thus tentatively disfavor models that globally increase the star formation efficiency (SFE) or the scatter in the M _UV – M _halo relation, while models that decrease the mass-to-light ratio, or assume a power-law scaling of the SFE with M _halo agree better with the data. We show that with sufficient additional independent sight lines, robust discrimination between models is possible, paving the way for powerful constraints on the physics of early galaxy evolution through NIRCam pure parallel imaging.

The central engines of Little Red Dots (LRDs) may be “black hole stars” (BH*s), early stages of black hole growth characterized by dense gas envelopes. So far, the most direct evidence for BH*s comes from a handful of sources where the host galaxy is completely outshone as suggested by their remarkably steep Balmer breaks. Here we present a novel scheme to disentangle BH*s from their host galaxies assuming that the [OIII]5008Å line arises exclusively from the host. Using a sample of 98 LRDs ( z ≈ 2 − 9 ) with high quality NIRSpec/PRISM spectra, we demonstrate that the host-subtracted median stack displays a Balmer break > 2 × stronger than massive quiescent galaxies, with the rest-optical continuum resembling a blackbody-like SED ( K, erg s, au). We measure a steep Balmer decrement (H α /H β > 10 ) and numerous density-sensitive features (e.g., FeII, HeI, OI). These are hallmark signatures of dense gas envelopes, providing population-level evidence that BH*s indeed power LRDs. In the median LRD, BH*s account for ∼ 20 % of the UV emission, ∼ 50 % at the Balmer break, and ∼ 90 % at wavelengths longer than H α with the remainder arising from the host. BH*s preferentially reside in low-mass galaxies () undergoing recent starbursts, as evidenced by extreme emission line EWs (e.g., [OIII]5008Å ≈ 1100 Å, CIII] ≈ 12 Å), thereby favoring BH* origins linked to star-formation. We show V-shaped LRD selections are biased to high BH*/host fractions ( ≳ 60 % at 5500Å) – less dominant BH*s may be powering JWST’s blue broad-line AGN. We find BH*s are so commonplace and transient (duty cycle ∼ 1 % , lifetime ∼ 10 Myrs) that every massive black hole may have once shone as a BH*.

In its first 2 yr of operation, the James Webb Space Telescope has enabled the discovery of a surprising number of UV-bright galaxies at z ∼ 10–14. Their number density is still relatively uncertain, due to cosmic variance effects, and the limited survey area with deep imaging. Here, we combine pure-parallel imaging from the PANORAMIC survey with data from legacy fields to constrain the bright end ( M _UV < −18.5) of the UV luminosity function (UVLF) over 0.28 deg ² of NIRCam imaging in six or more filters, and along 35 independent lines of sight. Using conservative color selections, we compile robust dropout samples at z ∼ 10, z ∼ 13, and z ∼ 17, and identify 16 new candidates from PANORAMIC. Our inferred UVLFs at z ∼ 10 are consistent with literature results and we confirm the high abundance of galaxies at the bright end ( M _UV ≲ −21) with better number statistics. We find somewhat lower number densities at z ∼ 13 compared to previous studies, and no robust candidates at z ∼ 17, indicating a rapid evolution of the galaxy population from z ∼ 10–17. The improved upper limits at z ∼ 17 imply that the cosmic UV luminosity density drops by at least a factor ∼50 from z ∼ 10 to z ∼ 17. Comparing our results to models proposed to explain the abundance of UV-bright galaxies at z ≳ 10, we conclude that a modest increase in the star formation efficiency, or in the burstiness of star formation, a more top-heavy initial mass function, a lack of dust attenuation, or a combination of these effects at z ≳ 10, is sufficient to match our observational constraints.

We investigate the nature and spectroscopic diversity of early galaxies from a sample of 41 sources at z ≥ 10 with JWST/NIRSpec prism observations. We compare the properties of strong UV line emitters, traced by intense C IV emission, with those of more “typical” sources with weak or undetected C IV. The more typical (or “C IV-weak”) sources reveal significant scatter in their C III] line strengths, UV continuum slopes, and physical sizes, spanning C III] equivalent widths of ∼1-51 Å, UV slopes of β ∼ −1.6 to −2.6, and half-light radii of ∼50-1000 pc. In contrast, C IV-strong sources occupy the tail of these distributions, with C III] EWs of 16-51 Å, UV slopes β ≲ −2.5, compact morphologies (r50 ≲ 100 pc), and elevated star formation surface densities (ΣSFR ≳ 100 M⊙ yr−1 kpc−2). These properties suggest concentrated starbursts that temporarily outshine the host galaxy. Comparing average properties from composite spectra, we find the diversity of the sample is primarily driven by bursty star formation on very short timescales (≤3 Myr), with strong C IV emitters observed at the apex of the bursts and sources devoid of emission lines during relative inactivity. An apparent association between strong C IV and enhanced nitrogen abundance suggests both may be modulated by the same duty cycle, reflecting a generic mode of star formation. We show that AGN are unlikely to contribute significantly to this duty cycle based on UV line diagnostics and photoionisation models. Our results support a picture whereby brief bursts and lulls can explain the spectral diversity and early growth of bright galaxies in the first 500 Myr.

We study the stellar mass function (SMF) of quiescent and star-forming galaxies and its dependence on morphology in ten redshift bins at 0.2 < z < 5.5. We used the COSMOS2025 catalog, built from the 0.54 deg ² JWST imaging from the COSMOS-Web survey, to select galaxies by type using the NUVrJ rest-frame color diagram and to classify them morphologically based on their bulge-to-total light ratio ( B / T ). The SMF of quiescent galaxies shows a rapid early build-up, with the most massive, log( M _★ /M _⊙ )≳11, being assembled by z ∼ 1 and evolving little since. The star-forming SMF evolves more slowly with redshift, following a mass-evolution scenario where galaxies grow in mass via star formation and quench once they reach the characteristic log( M ^∗ /M _⊙ ) ∼ 10.6. Bulge systems ( B / T > 0.6) dominate the quiescent SMF at log( M _★ /M _⊙ ) > 10 at all redshifts, while disk systems ( B / T < 0.2) dominate at log( M _★ /M _⊙ ) < 9. However, most bulge-dominated galaxies in the Universe are star forming, with their fraction increasing with redshift and decreasing mass, consistent with them being progenitors of quiescent bulges. We find evidence for the onset of environmental quenching as early as z ∼ 3 from the upturn in the quiescent SMF at log( M _★ /M _⊙ ) < 9.5. This upturn is contributed by disk-dominated galaxies, consistent with environmental quenching scenarios in which satellites are quenched, but retain their disk morphologies. The number densities of log( M _★ /M _⊙ ) > 10 quiescent galaxies are lower than in the recent literature by 0.1 − 0.7 dex, but agree well with cosmological galaxy formation simulations at 2 < z < 3. However, at z > 3, simulations increasingly underpredict the observations. Finally, we built a simple empirical model to describe the redshift evolution of galaxy number densities by parameterizing the quenching rate of all and bulge-dominated galaxies, stellar fraction, and bulge formation function. Our model is consistent with an evolutionary scenario where star-forming galaxies grow a central bulge before permanently quenching in massive halos.