We investigate the distribution and kinematics of cool circumgalactic medium (CGM) gas across the star-forming to quiescent transition using MgII absorption for 716 galaxies spanning 0.07<z<2.7 (169 new and 547 archival galaxies). To compare galaxies uniformly across 10 billion years of cosmic time, we introduce a star-formation offset metric (σ_SFO), which measures a galaxy's deviation from the star-forming main sequence of its epoch. A key advantage of σ_SFO is its ability to identify transitional green valley galaxies as a distinct population across redshift, which would otherwise be obscured by binary star-forming-passive classifications. We fit a virial-radius-normalized radial profile and find that the MgII absorption strength declines with increasing projected distance from the host galaxy. The scatter around this mean profile correlates strongly with star-formation activity: radial profile residuals correlate positively with log sSFR and σ_SFO, with star-forming galaxies showing excess absorption above the profile, green-valley galaxies showing intermediate residuals, and quiescent galaxies falling preferentially below it. The MgII covering fraction in the inner CGM (R/R_200 < 0.25) follows the same sequence, declining monotonically from star-forming through green-valley to quiescent systems. MgII absorption kinematics are consistent with a predominantly bound cool CGM. Star-forming galaxies further exhibit a bimodal azimuthal dependence, with MgII absorption enhanced along both the polar and disk directions, consistent with bipolar outflows and co-planar accretion. Together, these results indicate that the cool CGM tracks the quenching of star-formation in galaxies, with σ_SFO revealing a gradual decline in cool gas across the green valley rather than an abrupt star-forming-to-passive transition.

JWST has revealed a stunning population of bright galaxies at surprisingly early epochs, z>10, where few such sources were expected. Here we present the most distant example of this class yet – MoM-z14, a luminous (M_UV=-20.2) source in the COSMOS field at z_spec=14.44^+0.02_-0.02 that expands the observational frontier to a mere 280 million years after the Big Bang. The redshift is confirmed with NIRSpec/PRISM spectroscopy through a sharp Lyman-α break and ∼3σ detections of five rest-UV emission lines. The number density of bright z_spec∼14-15 sources implied by our "Mirage or Miracle" survey spanning ∼350 arcmin^2 is >100× larger (182^+329_-105×) than pre-JWST consensus models. The high EWs of UV lines (∼15-35 Å) signal a rising star-formation history, with a ∼10× increase in the last 5 Myr (SFR_5Myr/SFR_50Myr=9.9^+3.0_-5.8). The source is extremely compact (circularized r_e = 74^+15_-12 pc), and yet elongated (b/a=0.25^+0.11_-0.06), suggesting an AGN is not the dominant source of UV light. The steep UV slope (β=-2.5^+0.2_-0.2) implies negligible dust attenuation and a young stellar population. The absence of a strong damping wing provides tentative evidence that the immediate surroundings of MoM-z14 may be partially ionized at a redshift where virtually every reionization model predicts a ∼100% neutral fraction. The nitrogen emission and highly super-solar [N/C]>1 hint at an abundance pattern similar to local globular clusters that may have once hosted luminous supermassive stars. Since this abundance pattern is also common among the most ancient stars born in the Milky Way, we may be directly witnessing the formation of such stars in dense clusters, connecting galaxy evolution across the entire sweep of cosmic time.

Little Red Dots (LRDs) are a population of compact, red sources that have emerged as one of the most puzzling findings of JWST. Variability provides a direct probe of their central engines. Here we present the first joint spectroscopic and photometric time-domain study of LRDs undertaken with the JWST TWINKLE slitless spectroscopy program. Surveying the FRESCO GOODS-North legacy field, TWINKLE monitors a complete, Hα-flux-limited sample of 18 LRDs at z = 3.9-6.8, achieving a rest-frame baseline of ∼140-220 days. We detect no variability in photometry, Hα line flux, or line shape across the sample. If LRDs resembled AGN in reverberation mapping samples – the foundation for black hole mass calibrations and luminosity scaling relations – we would expect >10 sources to show measurable fluctuations. Observing none implies a 5.9σ deficit. The non-detections hold across all broad Hα emitters within TWINKLE's field of view – the 18 V-shaped LRDs as well as 9 non-LRDs. Comparison with simulated light curves disfavors sub-Eddington accretion and is instead consistent with super-Eddington accretion, other mechanisms that suppress variability, or perhaps no AGN whatsoever. If LRDs do harbor black holes, calibrations derived from sub-Eddington systems may not apply, thereby explaining JWST's apparently "overmassive" black holes. These observations provide unique constraints on the physics of one of the most enigmatic populations discovered by JWST.

The population of the little red dots (LRDs) may represent a key phase of supermassive black hole (SMBH) growth. A cocoon of dense excited gas is emerging as a key component to explain the most striking properties of LRDs, such as strong Balmer breaks and Balmer absorption, as well as the weak IR emission. To dissect the structure of LRDs, we analyzed new deep JWST/NIRSpec PRISM and G395H spectra of FRESCO-GN-9771, one of the most luminous known LRDs at z = 5.5. These spectra reveal a strong Balmer break, broad Balmer lines, and very narrow [O III] emission. We revealed a forest of optical [Fe II] lines, which we argue are emerging from a dense (nH = 109 − 10 cm−3) warm layer with electron temperature Te ≈ 7000 K. The broad wings of Hα and Hβ have an exponential profile due to electron scattering in this same layer. The high Hα : Hβ : Hγ flux ratio of ≈10.4 : 1 : 0.14 is an indicator of collisional excitation and resonant scattering dominating the Balmer line emission. A narrow Hγ component, unseen in the other two Balmer lines due to outshining by the broad components, could trace the ISM of a normal host galaxy with a star formation rate of ∼5 M⊙ yr−1. The warm layer is mostly opaque to Balmer transitions, producing a characteristic P Cygni profile in the line centers suggesting outflowing motions. This same layer is responsible for shaping the Balmer break. The broadband spectrum can be reasonably matched by a simple photoionized slab model that dominates the λ > 1500 Å continuum and a low-mass (∼108 M⊙) galaxy that could explain the narrow [O III], with only a subdominant contribution to the UV continuum. Our findings indicate that Balmer lines are not directly tracing the gas kinematics near the SMBH and that the BH mass scale is likely much lower than virial indicators suggest.

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 (T_eff 4050 K, log(L_bol) 43.9 erg s^-1, R_eff 1300 au). We measure a steep Balmer decrement (Hα/Hβ>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 Hα with the remainder arising from the host. BH*s preferentially reside in low-mass galaxies (M_⋆ 10^8 M_⊙) undergoing recent starbursts, as evidenced by extreme emission line EWs (e.g., [OIII]5008Å 1100Å, CIII] 12Å), 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*.

Close quasar pairs are rare products of galaxy mergers in which both supermassive black holes (SMBHs) are actively accreting, offering strong constraints on merger-driven active galactic nuclei evolution. Identifying close quasar pairs at z greater than or similar to 4 is challenging due to the declining quasar number density in the early Universe. Here we report the confirmation of a close quasar pair at z = 5.7, J2037-4537, utilizing high-resolution Atacama Large Millimeter/submillimeter Array observations. The quasar host galaxies exhibit tidal disturbed features in both the far-infrared continuum emission and the [C ii] line emission, ruling out the doubly imaged lensed quasar scenario. The two quasar hosts are massive (M-dyn greater than or similar to 10(10)M(circle dot)) and star-forming (star formation rate greater than or similar to 500M(circle dot) yr(-1)). The confirmation of J2037-4537 puts a lower limit on the quasar pair fraction at 5.5 < z < 6, F-pair > 1.2%, which is much higher than the quasar pair fraction at z less than or similar to 4. J2037-4537 is expected to form a gravitationally bound SMBH binary within less than or similar to 2 Gyr. The elevated quasar pair fraction at z > 5.5, as indicated by J2037-4537, likely contributes to the high gravitational-wave background reported by recent pulsar timing array experiments.

Abstract The Wide-field Infrared Transient Explorer (WINTER) is a near-infrared time-domain survey instrument operating on a dedicated robotic 1 m telescope at Palomar Observatory. Since June of 2023, WINTER has surveyed the sky nightly to a median depth of J AB = 18.5 mag. The survey balances a variety of science programs, including searching for kilonovae from gravitational-wave alerts, blind surveys to study galactic and extragalactic transients and variables, and building up reference images of the near-infrared sky. WINTER also demonstrates large-format Indium Gallium Arsenide (InGaAs) sensors as a new technology for wide-field near-infrared astronomy without cryogenic optics or detectors. A novel tiled fly’s-eye optical design allows WINTER to couple six non-buttable InGaAs sensors into a wide-field near-infrared camera with minimal chip gaps. The instrument covers a >1 deg 2 field of view with 1″ sampling. A filter exchanger enables observations in Y -, J -, or shortened- H -band filters (0.9–1.7 μ m). This paper presents the design and performance of the WINTER observatory, including the novel optical system, InGaAs detector performance, robotic survey operations, and highlights from the first years of on-sky science.

Episodic mass accretion is the dominant mechanism for mass assembly in the protostellar phase. Although prior optical time-domain searches have allowed detailed studies of individual outbursts, these searches remain insensitive to the earliest stages of star formation. In this paper, we present the characterization of two FU Orionis (FUor) outbursts identified using the combination of the ground-based, near-infrared Wide-field Infrared Transient Explorer (WINTER) and the space-based, mid-infrared NEOWISE survey. Supplemented with near-infrared spectroscopic follow-up, we show that both objects are bona fide FUor type outbursts based on (i) their proximity to star-forming regions, (ii) large amplitude (2–4 magnitudes) infrared brightening over the last decade, (iii) progenitor colors consistent with embedded (Class I) protostars, and (iv) “mixed-temperature” infrared spectra exhibiting characteristic signatures of cool outer envelopes and a hot inner disk with a wind. While one source, WNTR24-cua, is a known FUor that we independently recover; the second source, WNTR24-egv, is a newly confirmed object. Neither source is detected in contemporaneous ground-based optical imaging, despite flux limits ≳100× fainter than their infrared brightness, demonstrating the capabilities of WINTER to identify heavily obscured young stellar object outbursts. We highlight the capabilities of the Galactic Plane Survey of the recently commissioned WINTER observatory in addressing the poorly understood FUor population with its unique combination of real-time detection capabilities, multicolor sensitivity, weekly cadence, and wide area coverage.

We investigate the association between galaxies and neutral O i absorption systems at z similar to 6, which trace metal-enriched gas during the epoch of reionization. We identify 40 galaxies across six quasar fields, residing in 15 overdensities within 300 kpc of the background sight lines. Five O i absorption systems are associated with five of these overdensities, yielding a covering fraction of 0.27-0.10+0.13 within 300 kpc. The absorption occurs beyond typical virial radii, indicating that the gas traces extended overdensity environments rather than individual galaxy halos, unlike the z similar to 0 circumgalactic medium (CGM), which is largely bound to halos. These galaxy-associated absorbers account for similar to 35% of all O i systems seen in blind quasar surveys, implying the remainder arise in lower-mass galaxies below our detection threshold or in dense neutral intergalactic medium pockets. The CGM around these galaxies contains greater than or similar to 2 & times; 106 M circle dot of oxygen, comparable to the interstellar medium oxygen mass of the galaxies themselves, suggesting that the surrounding environment holds as much metal mass as the galaxies. All five galaxy-associated systems show significantly higher log(NCII/NOI) ratios than absorbers lacking galaxy associations. Furthermore, relative abundance ratios ([Si/O], [C/O]) reveal that four of the five exhibit enrichment patterns consistent with Population III nucleosynthesis at the outskirts of galaxy overdensities. These rare systems offer a unique window into the role of first-generation stars in shaping the early metal enrichment of galaxies and their environments.

In the nearby universe, quasars are well known to exhibit variability in their brightness over time, offering a powerful tool to probe the physics of accretion onto the supermassive black hole (SMBH) and directly measure the mass of the SMBH. However, detecting variability in early quasars remains challenging. Here we report the detection of multiwavelength infrared and X-ray variability in a quasar observed just 850 million years after the Big Bang. The infrared variability spans five filters, tracing rest-frame ultraviolet and optical emission from the accretion disk, while the X-ray variability probes the corona. The variable spectrum reveals that the accretion disk has a geometrically thin, optically thick structure. This provides observational constraints on the accretion disk structure at early times, when quasars are accreting at high Eddington ratios and reside in extreme environments. Our findings demonstrate the feasibility of characterizing accretion physics using variability in the early universe, laying the groundwork for studies exploiting upcoming facilities such as the Rubin Observatory and Roman Space Telescope. These facilities will discover large samples of variable high-redshift quasars, enabling population-level variability studies of accretion physics and black hole masses, filling key missing ingredients in understanding early SMBH growth.

We are developing the SuperFIRE concept, which builds on the heritage of the FIRE spectrograph at Magellan, as a broadband (about 340 nm to 2.5 um) intermediate resolution (R=10,000) single-shot natural seeing spectrograph for the Giant Magellan Telescope (GMT) with support from the Kavli Foundation. This single-object spectrograph is envisioned as a first-light instrument that can operate in natural seeing and grow in long-term capability as the telescope and adaptive optics systems mature. Here we discuss how the science cases and design have evolved since the concept was initially conceived and presented at SPIE in Edinburgh ten years ago. The primary drivers for the design changes are fast follow-up of faint transients and multi-messenger events, and complementarity to JWST observations in the infrared. By leveraging fast low-noise detectors and modern fabrication techniques we expect high throughput and low scatter that delivers sky limited performance in a few minutes of integration time for fast response and deep integrations. SuperFIRE will operate as a practical point-and-shoot follow-up spectrograph thanks to a versatile standard configuration that needs minimal observing or planning overheads and is insensitive to atmospheric conditions.

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 puzzle1. Several theoretical scenarios have been proposed to seed and rapidly grow black holes2-4, 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 hole5,6. 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 accretion7,8. 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 distributions9-11. The redness of the black hole is due to gas, not dust12,13, 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.

We present the GOLIATH survey (Galaxies, Outflows, and the Lifecycle of Immense, Active, Transforming Halos), a study of the multiphase circumgalactic medium (CGM) of massive (⟨log M_⋆/M_⊙⟩≈ 11), blue (u-r < 1.65) starburst and post-starburst galaxies at ⟨ z⟩≈ 0.43. This work characterizes the warm-hot CGM through OVI absorption in the inner halo (R/R_ vir≤ 0.6) of these rare systems. Across the star-forming population, OVI column density rises by nearly 1 dex from log M_⋆/M_⊙∼ 8 to ∼ 11.5 and increases with specific star-formation rate (sSFR). Two GOLIATH galaxies with the highest sSFR show the strongest CGM OVI absorption (log N_ O VI[ cm^-2] ≳ 15). In the log M_⋆/M_⊙ = [11,12) inner-CGM region, massive star-forming galaxies exceed quiescent galaxies on average by a factor of ∼ 3 in OVI column density and ∼ 1.5 dex in CGM OVI mass (log(M_ O VI/M_⊙) ≈ 7.3 versus ≈ 5.8), with covering fractions roughly three times higher (62.5

Measurements of quasar lifetimes at high redshift indicate that the earliest billion-solar-mass supermassive black holes (SMBHs) have only been active as luminous quasars for less than a million years. Recently, extended Ly alpha nebulae around z similar to 6 quasars have revealed that these short observed lifetimes are unlikely to be a sight-line-dependent effect. However, the interpretation of Ly alpha emission is not straightforward due to its resonant nature. In this work, we use rest-frame optical emission lines, which more directly trace photoionization by the quasar, to unambiguously validate the short line-of-sight quasar lifetimes observed at early cosmic epochs. We use deep James Webb Space Telescope/NIRSpec integral field unit observations of five z similar to 6 quasars with small proximity zones to search for their extended emission line nebulae in H alpha and [O III]5007, and detect extended emission in both emission lines around four quasars in our sample. We then use the light-crossing time of these nebulae to measure quasar lifetimes along transverse sight lines. Using their H alpha nebulae, we also confirm that recombination is likely the dominant emission mechanism behind their previously detected Ly alpha nebulae. Our results confirm the existence of high-redshift quasars with extremely short lifetimes, tQ less than or similar to 105 yr, hosting billion-solar-mass black holes, indicating that rapid or obscured accretion is likely responsible for the assembly of SMBHs in the early Universe.

Little Red Dots (LRDs) display singular properties unlike any known class of AGN or galaxies, motivating novel mass estimators for their central engines. Inspired by their similarities to stellar phenomena, here we interpret the LRD continuum as being produced by a pseudo-photosphere. We fit tailored stellar atmosphere models to host-subtracted LRD central engines ("black hole stars," BH*s) represented by stacks of 117 objects. Typical BH* continuum spectra are well fit by models in a narrow range of temperatures (T_ eff≈4200-4800 K), with bolometric luminosities ≈10^43-45 erg s^-1, implying pseudo-photospheric radii ≈700-2000 au. Based on these parameters, we explore four different approaches to deriving BH* masses: 1) using the surface gravity from atmosphere models; 2) appealing to the resemblance to super-Eddington phenomena; 3) approximating the escape velocity from the outflowing material; and 4) exploiting the lack of variability to bound the dynamical time. For the typical BH*, all of these methods yield remarkably consistent masses of ≈10^4-5 M_⊙, implying a highly super-Eddington luminosity of L_bol/L_Edd∼5-50. These mass estimates place BH*s within the scatter of the local scaling relation between black hole mass and host galaxy stellar mass, providing a self-consistent alternative to "overmassive" black holes that lie 2-3 dex above it. Crucially, our derived masses are consistent with BH*s arising from single supermassive stars (SMSs), whose masses cannot exceed ≈10^5-6 M_⊙ due to general relativistic instabilities. Furthermore, for our derived L_ bol/L_ Edd, the sharp cutoff of the LRD luminosity function matches the maximum theoretical mass of an SMS. With LRDs, we may therefore be directly observing the birth of heavy black hole seeds.

The origin of dust in the early Universe remains uncertain. We explore whether Little Red Dots (LRDs) could provide a high-redshift dust-production channel. Motivated by an analogy with Type IIn supernovae, we investigate whether LRDs may share the efficient dust-forming conditions. We consider dust formation in outer winds and later in a shielded cold dense shell after the central source fades. Such dust may avoid a global remnant-phase reverse shock, while longer LRD lifetimes may promote grain growth. We model the SEDs of two low-redshift LRD analogs as a thermal pseudo-photosphere plus optically thin dust components, obtaining dust reservoirs of order 10^2-10^3 M_⊙. Although photometry cannot exclude pre-existing dust, the narrow Balmer components of both analogs are close to the Case B ratio and their narrow-line environments are metal-poor, disfavoring a dominant diffuse host-ISM origin for the inferred reservoir. Formation within the LRD outflow is consistent with our optical-depth, sublimation, and energy-balance checks. In this scenario, the large dust masses do not produce a strong optical attenuation because a clumpy or asymmetric distribution can leave the dominant optical sightlines relatively unobscured. Our population calculation shows that the LRD contribution to early-Universe dust production can range from negligible to dominant. At higher efficiencies, LRDs can approach or exceed the lower CCSN contribution above z≈5, whereas less favorable assumptions yield a minor contribution. We therefore propose that LRDs can act as early-Universe dust factories and, under some conditions, may dominate over CCSNe or provide seed grains for subsequent growth in the early ISM.

JWST's Little Red Dots (LRDs) display a unique constellation of features that do not occur simultaneously in any other class of galaxies or AGN. Here we observe that many of these features find parallels in the 19th century Great Eruption (GE) of η Carinae and a sub-class of supernovae (Type IIn). Drawing on these stellar phenomena – outflows trapped by dense circumstellar gas envelopes – we sketch a possible scenario for LRDs. Outflows from the central engine produce an enshrouding envelope of gas that may be thought of as a slow wind. This dense wind and its enormous extent produce an opacity so high that a pseudo-photosphere forms within the wind, obscuring the central engine and manifesting as a blackbody-like continuum. Radiation from the buried engine powers the system. The engine may also launch fast winds that crash into the existing envelope to generate shocks. Lines form within the wind above the photosphere – electron scattering and absorption in the clumpy (ionized + neutral) medium account for broad wings and P-Cygni cores. A key implication is that inferences of “overmassive black holes" may be interpreting this wind-like physics as a virial broad-line region. We propose an escape velocity argument to constrain the mass of the engine, which yields M<10^5 M_⊙ for the typical LRD. The lack of variability and low surface gravity of the photosphere provide further support for intermediate mass (M≈10^3-6 M_⊙), but very luminous super-Eddington (L_bol/L_edd≳5) systems harboring a supermassive star or intermediate mass black hole. Paralleling the evolution of IIn SNe, dust production in the envelope may mark the beginnings of classical AGN. This paper explores a possible self-consistent explanation for the entire life-cycle of LRDs, from their enshrouding in dense gas to their fates as seeds of massive black holes.

When a massive star reaches the end of its lifetime, its core collapses and releases neutrinos that drive a shock into the outer layers (the stellar envelope). A sufficiently strong shock ejects the envelope, producing a supernova. If the shock fails to eject it, the envelope is predicted to fall back onto the collapsing core, producing a stellar-mass black hole (BH) and causing the star to disappear. We report observations of M31-2014-DS1, a hydrogen-depleted supergiant in the Andromeda Galaxy. In 2014, it brightened in the mid-infrared, then from 2017 to 2022, it faded by factors of [Formula: see text] in optical light (becoming undetectable) and [Formula: see text] in total light. We interpret these observations, and those of a previous event in NGC 6946, as evidence for failed supernovae forming stellar-mass BHs.

We present JWST/NIRCam F070W and F480M imaging for a quasar at z = 5.07, J0025-0145, which is magnified by a foreground lensing galaxy. Existing Hubble Space Telescope (HST) imaging does not have sufficient spatial resolution to determine whether the background quasar is multiply imaged. Exploiting the sharp point-spread function (PSF) of the F070W band, we confirm that the background quasar can be well described by a single PSF, essentially ruling out the existence of multiple lensed images. We do not detect the quasar host galaxy in either the F070W or the F480M band. Using the HST and JWST photometry, we fit the spectral energy distribution of the foreground galaxy. The estimated mass (log(M (*)/M-circle dot = 11.15 +/- 0.16) and redshift (z(phot) = z 3.62(- 0.04) (+ 0.06)) of the foreground galaxy are consistent with a single-image lensing model. We estimate the maximum possible magnification of the quasar to be mu(max) = 3.2, which implies that the intrinsic Eddington ratio of the quasar is at least lambda(Edd) (intrinsic) > 4.9. Therefore, J0025-0145 has one of the highest Eddington ratios among z > 5 supermassive black holes known so far, suggesting the viability of super-Eddington growth for supermassive black holes in the early Universe.