Yichen Liu

We report the discovery of a galaxy protocluster candidate (dubbed MACS0416-OD-z8p5) at a spectroscopic redshift of z ∼ 8.47, dating back to ∼550 Myr after the Big Bang. The observations are part of the JWST Cycle 3 Treasury Program Slitless Areal Pure-Parallel HIgh-Redshift Emission Survey (or SAPPHIRES) using NIRCam grism observations. Using wide-field slitless spectroscopy (WFSS) obtained in the MACS0416 parallel field, we robustly confirm nine galaxies at z _spec ∼ 8.47 via emission-line detections of [O iii ] 5008 Å (with >5 σ ) and tentatively confirm one additional galaxy (at ∼3 σ ). This discovery represents the highest-redshift spectroscopically confirmed galaxy overdensity known to date and is ∼6–8 times more dense than the average number density of galaxies at the same redshift. Furthermore, a galaxy hosting a low-mass active galactic nucleus (a “little red dot”) is found as a member, suggesting that black hole growth may already be underway in dense environments at early cosmic times. This finding of a massive dark matter halo hosting a galaxy overdensity at z ∼ 8.5 is surprising given that our survey covered only a small, random field ( 16.5 arcmin 2 ) as part of a pure-parallel observation. Comparison with cosmological simulations shows that the likelihood of finding such a large-scale structure is <5% under the current galaxy formation scenario and within the observed survey volume. Our results demonstrate the power of WFSS observations for building complete samples of line-emitting galaxies and suggest an important role for overdensities in enhancing galaxy formation by funneling large-scale gas supplies into small cosmological volumes.

Near-IR Paschen lines are potentially excellent tracers of Type 1 active galactic nuclei (AGNs) that is hardly affected by dust extinction. JWST allows us, for the first time, to explore Paschen-line objects at redshift z > 1. Here we present a study of 62 AGNs with broad Pa α and Pa β lines at 1 < z < 3 using data from the JWST COSMOS-3D program. These AGNs are efficiently selected and identified using NIRCam imaging and grism slitless spectroscopic data. We separate the AGN-host emission with image decomposition and quantify dust attenuation with multiband data. We construct a calibration sample with optical spectroscopy and use single-epoch, Mg ii -based black hole masses ( M _BH ) as an anchor to derive new, Paschen-based M _BH estimators. We obtain three sets of M _BH estimators based on Paschen line luminosities and AGN continuum luminosities at 1 and 2 μ m, respectively. After dust corrections, they are well consistent with each other, and also broadly agree with previous results. With this AGN sample, we further construct the first Pa α and Pa β luminosity functions (LFs) of Type 1 AGNs. The derived LFs are 3–5 times higher than those of UV/optical-selected AGNs, indicating that Paschen-selected Type 1 AGNs are more complete. In addition, the intrinsic properties of our AGNs show no dependence on dust reddening, suggesting that the observed reddening is unrelated to the central engine and is thus likely caused by line-of-sight obscuration.

Feedback from accreting supermassive black holes may regulate galaxy evolution, but statistical evidence linking nuclear winds to kiloparsec-scale cold gas outflows remains limited in the early Universe. Here, we report statistical evidence for such a connection in a sample of luminous quasars at z ∼ 5.5. We compare stacked [C ii ] 158 μ m emission profiles from Atacama Large Millimeter/submillimeter Array observations, which trace galactic-scale neutral gas, for quasars with and without broad absorption lines (BALs) that indicate powerful nuclear winds on subkiloparsec scales. A total of 5 BAL and 11 non-BAL quasar spectra are included in the stacking analysis. The BAL quasar stack exhibits a potential blueshifted broad component in the [C ii ] line profile, with a velocity offset of Δ v _b = −2.1 × 10 ² km s ⁻¹ and a full width at half-maximum of 1.18 × 10 ³ km s ⁻¹ , whereas the non-BAL stack shows no obvious broad component. Using a conservative “clean-stack” selection that excludes quasars with partial [C ii ] spectral coverage, the BAL broad residual is reduced to a hint-level feature. We estimate that up to a few percent to one quarter of the nuclear wind energy may be transferred to cold neutral gas on kiloparsec scales. Although the sample size is limited, these results suggest a potential link between BAL winds and cold gas feedback in quasar host galaxies. These results provide empirical motivation for future tests of how multiphase outflows relate to the diversity of quasar host properties, including M _BH / M _* .

Luminous quasars at the redshift frontier z > 7 serve as stringent probes of super-massive black hole (SMBH) formation and they are thought to undergo much of their growth obscured by dense gas and dust in their host galaxies. Fully characterizing the symbiotic evolution of SMBHs and hosts requires rest-frame optical observations that span spatial scales from the broad-line region (BLR) to the interstellar and circumgalactic medium (ISM and CGM). The James Webb Space Telescope (JWST) now provides the necessary spatially resolved spectroscopy to do so. However, the physical conditions that regulate the interplay between SMBHs and their hosts at the highest redshifts, especially the nature of early feedback phases, remain unclear. We present JWST/NIRSpec integral field unit (IFU) observations of J0313−1806 at z = 7.64, the most distant luminous quasar known. From the rest-frame optical spectrum of the unresolved quasar, we derived a black hole mass of M _BH = (1.63 ± 0.10)×10 ⁹ M _⊙ based on H βλ 4861 (H β ) and an Eddington rate of λ = L / L _Edd = 0.80 ± 0.05, consistent with previous Mg II λ 2800-based estimates. J0313–1806 exhibits no detectable [O III ] λλ 4959, 5007 emission on nuclear scales (3 σ upper limit equivalent width of [O III ] λ 5007 < 1.42 Å). Most remarkably, we did detect an ionized gas shell extending out to ∼1.8 kpc traced by H β emission that also lacks any significant [O III ] λλ 4959, 5007, with a 3 σ upper limit on the [O III ] λ 5007 to H β flux ratio of log ₁₀ ( F ([O III ])/ F (H β )) = −1.15. Through photoionization modeling, we demonstrate that the extended emission is consistent with a thin, clumpy outflowing shell where [O III ] is collisionally de-excited by dense gas. We interpret this structure as a fossil remnant of a recent blowout phase, providing evidence for episodic feedback cycles in one of the earliest quasars. These findings suggest that dense ISM phases may play a crucial role in shaping the spectral properties of quasars across cosmic time.

JWST observations have revealed a population of high-redshift “little red dots” (LRDs) that challenge conventional active galactic nucleus (AGN) models. We report the discovery of three local LRDs at z = 0.1–0.2, initially selected from the Sloan Digital Sky Survey database, with follow-up optical/near-IR spectroscopy and photometry. They exhibit properties fully consistent with those of high-redshift LRDs, including broad hydrogen and helium emission lines, compact morphologies, V-shaped UV-optical spectral energy distribution, declining near-IR continua, and no significant variability. Two sources were targeted but not detected in X-rays with statistical significance. All three sources show blue-shifted He i absorption, while two exhibit H α and Na D absorption lines. We detect full Balmer and Paschen line series in all three objects, along with abundant narrow [Fe ii ] emission in two. The emission-line analyses suggest narrow lines originate from AGN-powered, metal-poor regions with minimal dust; broad lines come from inner regions with exceptionally high density or atypical dust properties; and [Fe ii ] emission arises from dense gas between broad- and narrow-line regions. One of our objects, J1025+1402 (nicknamed “The Egg”), shows extremely high equivalent width Na D, K i , and Ca ii triplet absorption lines, along with other potential low-ionization absorption features, suggesting the presence of a cool (∼5000 K), metal-enriched gas envelope. The optical/near-IR continua of these LRDs are also consistent with theoretical models featuring an atmosphere around black holes (BHs). The Wide-field Infrared Survey Explorer–detected IR emission is consistent with weak dust emission of T ∼ 10 ² –10 ³ K. We propose a conceptual model consisting of a largely thermalized cool-gas envelope surrounding the central BH and an extended emission-line region with high-density outflowing gas to explain the observed properties of these local LRDs.

We present new Chandra observations of seven luminous quasars at z > 6.5. Combined with archival Chandra observations of all other known quasars, they form nearly complete X-ray observations of all currently known z ∼ 7 quasars with M ₁₄₅₀ < –26.5, except for J0313−1806 at z = 7.642 and J0910−0414 at z = 6.636. Together with existing ground-based near-infrared spectroscopy and Atacama Large Millimeter Array observations, we investigate the correlations between X-ray emission (the X-ray luminosity L _X and the optical/UV-to-X-ray spectral slope α _OX ) and various quasar properties (rest-UV luminosity L _{2500 Å} , bolometric luminosity L _bol , C iv blueshift, and infrared luminosity L _IR ). We find most z > 6.5 quasars follow a similar α _OX – L _{2500 Å} relation as z ∼ 1–6 quasars, but also display a large scatter. We find a potential correlation between α _OX and the C iv blueshift, suggesting a soft optical/UV-to-X-ray spectral energy distribution shape is frequently associated with fast disk winds. Furthermore, we analyze the X-ray spectrum of 11 quasars at z > 6.5 with Chandra detection, and find that the best-fit photon index, Γ, is 2.41 ± 0.27, which is likely driven by high accretion rates of z > 6.5 quasars. In addition, we find there are no significant correlations between either L _X and L _IR , nor L _bol and L _IR , suggesting no strong correlations between quasar luminosity and star formation luminosity for the most luminous quasars at z > 6.5.

We report the discovery of 13 broad-line active galactic nuclei (AGNs) at z = 5–8 from the first 10% of JWST Cycle 3 Treasury Program COSMOS-3D. These AGNs are identified by their broad H α or H β emission lines through NIRCam grism slitless spectroscopy. One object at z = 7.646 with broad H β emission has an F444W magnitude of 23.6 mag, making it one of the brightest z > 7.5 broad-line AGNs yet known. Among the 13 AGNs, 10 objects exhibit reddened optical continua with slopes β _opt > 0. The remaining three resemble UV-luminous quasars at similar redshift but with β _opt less blue than those of typical unobscured quasars. We also obtain MIRI photometry (7.7–18 μ m) for two AGNs and place strong constraints on their rest-frame near-IR spectral energy distribution. We find no significant variability in the rest-frame UV by comparing the COSMOS-3D and COSMOS-Web F115W images taken apart by 60 days in the rest-frame. We compute the H α luminosity function (LF) at z ≈ 5–6 and find potential redshift evolution compared to z ≈ 4–5. We also derive the H β LF at z ∼ 8 by combining our sample with those from the literature. The broad H β emitters in this work suggest a number density 2 orders of magnitude higher than that predicted by the quasar LF based on rest-frame UV-selected samples. As a preview, our work showcases the ability of the COSMOS-3D grism survey to provide a complete view of the properties, growth, and evolution of bright broad-line AGNs at z > 5.

We study the black hole mass–host galaxy stellar mass relation, M _BH – M _* , for a sample of 706 z ≲ 1.5 and i ≲ 24 optically variable active galactic nuclei (AGNs) in three Dark Energy Survey (DES) Deep Fields: C3, X3, E2, which partially cover Chandra Deep Field-South, XMM Large Scale Structure survey, and European Large Area ISO Survey, respectively. The parent sample was identified by optical variability from the DES supernova survey program imaging. Using publicly available spectra and photometric catalogs, we consolidate their spectroscopic redshifts, estimate their black hole masses using broad line widths and luminosities, and obtain improved stellar masses using spectral energy distribution fitting from X-ray to mid-infrared wavelengths. Our results confirm previous work from Hyper-Suprime Camera imaging that variability searches with deep, high-precision photometry can reliably identify AGNs in low-mass galaxies up to z ∼ 1. However, we find that the hosted black holes are more massive than predicted by the local AGN relation, fixing host galaxy stellar mass. Instead, z ∼ 0.1–1.5 variability-selected AGNs lie in between the M _BH – M _* relation for local inactive early-type galaxies and local active galaxies. This result agrees with most previous studies of the M _BH – M _* relation for AGNs at similar redshifts, regardless of the selection technique. We demonstrate that studies of variability-selected AGN provide critical insights into the low-mass end of the M _BH – M _* relation, shedding light on the occupation fraction of that provides constraints on early black hole seeding mechanisms and self-regulated feedback processes during their growth and coevolution with their hosts.