The first few 100 Myr at z > 10 mark the last major uncharted epoch in the history of the universe, where only a single galaxy (GN-z11 at z ≈ 11) is currently spectroscopically confirmed. Here we present a search for luminous z > 10 galaxies with JWST/NIRCam photometry spanning ≈1–5 μm and covering 49 arcmin2 from the public JWST Early Release Science programs (CEERS and GLASS). Our most secure candidates are two M UV ≈ −21 systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt ≳1.8 mag breaks in their spectral energy distributions (SEDs), consistent with complete absorption of flux bluewards of Lyα that is redshifted to z = 12.4 − 0.3 + 0.1 and z = 10.4 − 0.5 + 0.4 . Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at >5σ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up ∼109 solar masses in stars over the ≲300–400 Myr after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of r 50 ≈ 0.7 kpc. These sources, if confirmed, join GN-z11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area >10× larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep JWST observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated.

JWST 's first glimpse of the z > 10 Universe has yielded a surprising abundance of luminous galaxy candidates. Here we present the most extreme of these systems: CEERS-1749. Based on 0.6 − 5µm photometry, this strikingly luminous (≈26 mag) galaxy appears to lie at z ≈ 17. This would make it an M UV ≈ −22, M ≈ 5 × 10 9 M system that formed a mere ∼ 220 Myrs after the Big Bang. The implied number density of this galaxy and its analogues challenges virtually every early galaxy evolution model that assumes ΛCDM cosmology. However, there is strong environmental evidence supporting a secondary redshift solution of z ≈ 5: all three of the galaxy's nearest neighbors at < 2.5 have photometric redshifts of z ≈ 5. Further, we show that CEERS-1749 may lie in a z ≈ 5 protocluster that is 5× overdense compared to the field. Intense line emission at z ≈ 5 from a quiescent galaxy harboring ionized gas, or from a dusty starburst, may provide satisfactory explanations for CEERS-1749's photometry. The emission lines at z ≈ 5 conspire to boost the > 2µm photometry, producing an apparent blue slope as well as a strong break in the SED. Such a perfectly disguised contaminant is possible only in a narrow redshift window (∆z 0.1), implying that the permitted volume for such interlopers may not be a major concern for z > 10 searches, particularly when medium-bands are deployed. If CEERS-1749 is confirmed to lie at z ≈ 5, it will be the highest-redshift quiescent galaxy, or one of the lowest mass dusty galaxies of the early Universe detected to-date (A 5500 ≈ 1.2 mag, M ≈ 5 × 10 8 M ). Both redshift solutions of this intriguing galaxy hold the potential to challenge existing models of early galaxy evolution, making spectroscopic follow-up of this source critical.

The first few hundred Myrs at z > 10 mark the last major uncharted epoch in the history of the Universe, where only a single galaxy (GNz11 at z ≈ 11) is currently spectroscopically confirmed. Here we present a search for luminous z > 10 galaxies with JWST /NIRCam photometry spanning ≈ 1 − 5µm and covering 49 arcmin 2 from the public JWST Early Release Science programs (CEERS and GLASS). Our most secure candidates are two M UV ≈ −21 systems: GLASS-z13 and GLASS-z11. These galaxies display abrupt 2.5 mag breaks in their spectral energy distributions, consistent with complete absorption of flux bluewards of Lyman-α that is redshifted to z ≈ 13 and z ≈ 11. Lower redshift interlopers such as dusty quiescent galaxies with strong Balmer breaks would be comfortably detected at > 5σ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up ∼ 10 9 solar masses in stars over the 300−400 Myrs after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z11 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of r 50 ≈ 0.7 kpc. These sources, if confirmed, join GNz11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area > 10× larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn

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We study the incidence of nuclear activity in a large sample of massive post-starburst galaxies at z ∼ 0.7 selected from the Sloan Digital Sky Survey, and identify active galactic nuclei based on radio continuum and optical emission lines. Over our mass range of 10 10.6 −10 11.5 M , the incidence of radio activity is weakly dependent on stellar mass and independent of stellar age, while radio luminosity depends strongly on stellar mass. Optical nuclear activity incidence depends most strongly on the D n4000 line index, a proxy for stellar age, with an active fraction that is ∼ ten times higher in the youngest versus oldest post-starburst galaxies. Since a similar trend is seen between age and molecular gas fractions, we argue that, like in local galaxies, the age trend reflects a peak in available fueling rather than feedback from the central black hole on the surrounding galaxy.

We use ALMA observations of CO(2–1) in 13 massive (M * ≳ 1011 M ⊙) poststarburst galaxies at z ∼ 0.6 to constrain the molecular gas content in galaxies shortly after they quench their major star-forming episode. The poststarburst galaxies in this study are selected from the Sloan Digital Sky Survey spectroscopic samples (Data Release 14) based on their spectral shapes, as part of the Studying QUenching at Intermediate-z Galaxies: Gas, angu L → ar momentum, and Evolution ( SQuIGG L ⃗ E ) program. Early results showed that two poststarburst galaxies host large H2 reservoirs despite their low inferred star formation rates (SFRs). Here we expand this analysis to a larger statistical sample of 13 galaxies. Six of the primary targets (45%) are detected, with M H 2 ≳ 10 9 M ⊙. Given their high stellar masses, this mass limit corresponds to an average gas fraction of 〈 f H 2 ≡ M H 2 / M * 〉 ∼ 7 % or ∼14% using lower stellar masses estimates derived from analytic, exponentially declining star formation histories. The gas fraction correlates with the D n 4000 spectral index, suggesting that the cold gas reservoirs decrease with time since burst, as found in local K+A galaxies. Star formation histories derived from flexible stellar population synthesis modeling support this empirical finding: galaxies that quenched ≲150 Myr prior to observation host detectable CO(2–1) emission, while older poststarburst galaxies are undetected. The large H2 reservoirs and low SFRs in the sample imply that the quenching of star formation precedes the disappearance of the cold gas reservoirs. However, within the following 100–200 Myr, the SQuIGG L ⃗ E galaxies require the additional and efficient heating or removal of cold gas to bring their low SFRs in line with standard H2 scaling relations.

We describe the Studying Quenching in Intermediate-z Galaxies: Gas, angu L → ar momentum, and Evolution ( SQuIGG L ⃗ E ) survey of intermediate-redshift post-starburst galaxies. We leverage the large sky coverage of the Sloan Digital Sky Survey to select ∼ 1300 recently quenched galaxies at 0.5 < z ≤ 0.9 based on their unique spectral shapes. These bright, intermediate-redshift galaxies are ideal laboratories to study the physics responsible for the rapid quenching of star formation: they are distant enough to be useful analogs for high-redshift quenching galaxies, but low enough redshift that multiwavelength follow-up observations are feasible with modest telescope investments. We use the Prospector code to infer the stellar population properties and nonparametric star formation histories (SFHs) of all galaxies in the sample. We find that SQuIGG L ⃗ E galaxies are both very massive (M * ∼ 1011.25 M ⊙) and quenched, with inferred star formation rates ≲1 M ⊙ yr−1, more than an order of magnitude below the star-forming main sequence. The best-fit SFHs confirm that these galaxies recently quenched a major burst of star formation: >75% of SQuIGG L ⃗ E galaxies formed at least a quarter of their total stellar mass in the recent burst, which ended just ∼200 Myr before observation. We find that SQuIGG L ⃗ E galaxies are on average younger and more burst-dominated than most other z ≲ 1 post-starburst galaxy samples. This large sample of bright post-starburst galaxies at intermediate redshift opens a wide range of studies into the quenching process. In particular, the full SQuIGG L ⃗ E survey will investigate the molecular gas reservoirs, morphologies, kinematics, resolved stellar populations, active galactic nucleus incidence, and infrared properties of this unique sample of galaxies in order to place definitive constraints on the quenching process.

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