Galaxies are often modeled as composites of separable components with distinct spectral signatures, implying that different wavelength ranges are only weakly correlated. They are not. We present a data-driven model that exploits subtle correlations between physical processes to accurately predict infrared (IR) Wide-field Infrared Survey Explorer (WISE) photometry from a neural summary of optical Sloan Digital Sky Survey spectra. The model achieves accuracies of chi N2 approximate to 1 for all photometric bands in WISE, as well as good colors. We are able to tightly constrain typically IR-derived properties, e.g., the bolometric luminosities of active galactic nuclei (AGN) and dust parameters such as qPAH. We also test whether current spectral energy distribution (SED) fitting methods reproduce such panchromatic relations, but find their predictions biased and overconfident, likely due to model misspecification, with correlated biases in star-formation rates (SFRs) and AGN luminosities being most evident. To help improve SED models, we determine which features of the optical spectrum are responsible for our improved predictions, and identify several lines (Ca II, Sr II, Fe I, [O II], and H alpha), which point to the complex chronology of star formation and chemical enrichment being incorrectly modeled.

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*.

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.

Feedback from active galactic nuclei (AGN) is widely acknowledged to regulate the growth of massive galaxies, though its driving mechanisms are debated. Prevailing theories suggest that AGN-driven outflows are driven either by radiation pressure acting directly on the dusty interstellar medium (ISM) or by hot winds entraining cooler ISM gas, but the relative contribution of each mechanism remains uncertain. By combining optical emission line measurements with highly ionized UV emission lines, it is possible to constrain whether the pressure source applied to ionized clouds is primarily radiation or primarily hydrodynamic, and thus constrain the dominant driver. This study presents the first multi-object analysis of far-ultraviolet (FUV) spectra from galactic-scale AGN-driven outflows in obscured quasars, based on Cosmic Origins Spectrograph observations of five low-redshift targets. By comparing narrow-line region UV emission line ratios to theoretical models that vary the importance of the two pressure sources, we find three out of five targets fall within the radiation pressure-dominated regime. A fourth target exhibits intermediate emission-line ratios that suggest radiation pressure and pressure from a hot wind are both dynamically important. Finally, the lowest-luminosity object in our sample may have a dynamically important hot wind component, but non-detections prevent a clear conclusion in this case. These results suggest radiation pressure dominates circum-nuclear narrow-line region cloud dynamics, but pressure from a hot wind also plays a role in some cases. This is consistent with AGN feedback scenarios mediated by radiation pressure or a short-lived hot wind phase that dissipates after initially accelerating outflows.

We present new Very Long Baseline Array (VLBA) imaging of a megahertz peaked-spectrum source that was found using commensal low-frequency data taken with the Karl G. Jansky Very Large Array (VLA). The source, J0330–2730, was identified in multiepoch data from the VLA Low-band Ionosphere and Transient Experiment (VLITE). VLITE continuously collects low-frequency data at 340 MHz during regular VLA observations. Our analysis of the VLITE light curve demonstrates that J0330–2730 has significant 340 MHz flux variability at the ∼20% level over a timescale of approximately 1 yr. Our VLBA images reveal a resolved, double-lobed morphology with a projected linear size of 64 pc. We consider plausible mechanisms that could explain the observed 340 MHz variability and the source properties on milliarcsecond scales. We rule out variable Doppler boosting and conclude that refractive interstellar scintillation or variable free–free absorption are the most likely explanations. We argue that the properties of J0330–2730 are consistent with the class of compact symmetric objects and consider the evolutionary stage of the source. The extent of the resolved lobes revealed by the VLBA is significantly smaller than predictions based on the turnover–size relation for a standard synchrotron self-absorbed jet model. We discuss possible explanations for the departure from the turnover–size relation, including jet formation by a transient phenomenon such as a tidal disruption event or a “frustrated jet” impeded by the presence of dense gas or a high-pressure environment. This study highlights the potential of VLITE for the identification of compact and young radio sources.

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.

Feedback from active galactic nuclei (AGN) is widely acknowledged to regulate the growth of massive galaxies, though its driving mechanisms are debated. Prevailing theories suggest that AGN-driven outflows are driven either by radiation pressure acting directly on the dusty interstellar medium (ISM) or by hot winds entraining cooler ISM gas, but the relative contribution of each mechanism remains uncertain. By combining optical emission line measurements with highly ionized UV emission lines, it is possible to constrain whether the pressure source applied to ionized clouds is primarily radiation or primarily hydrodynamic, and thus constrain the dominant driver. This study presents the first multiobject analysis of far-UV spectra from galactic-scale AGN-driven outflows in obscured quasars, based on Cosmic Origins Spectrograph observations of five low-redshift targets. By comparing narrow-line region UV emission-line ratios to theoretical models that vary the importance of the two pressure sources, we find that three out of five targets fall within the radiation-pressure-dominated regime. A fourth target exhibits intermediate emission-line ratios that suggest radiation pressure and pressure from a hot wind are both dynamically important. Finally, the lowest-luminosity object in our sample may have a dynamically important hot wind component, but nondetections prevent a clear conclusion in this case. These results suggest radiation pressure dominates circumnuclear narrow-line region cloud dynamics, but pressure from a hot wind also plays a role in some cases. This is consistent with AGN feedback scenarios mediated by radiation pressure or a short-lived hot wind phase that dissipates after initially accelerating outflows.

Internal gas inflows driven by galaxy mergers are considered to enhance star formation rates (SFR), fuel supermassive black hole growth and stimulate active galactic nuclei (AGN). However, quantifying these phenomena remains a challenge, due to difficulties both in classifying mergers and in quantifying galaxy and AGN properties. We quantitatively examine the merger-SFR-AGN connection using Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) galaxies using novel methods for both galaxy classification and property measurements.} {Mergers in HSC-SSP observational images are identified through fine-tuning Zoobot, a pretrained deep representation learning model, using images and labels based on the Galaxy Cruise project. We use galaxy and AGN properties that were produced by fitting Galaxy and Mass Assembly (GAMA) spectra using the SED fitting code ProSpect, which fits panchromatically across the far-UV through far-infrared wavelengths and obtains galaxy and AGN properties simultaneously.} \textbf{{Little differences are seen in SFR and AGN activity between mergers and controls, with $\Delta \mathrm{SFR}=-0.009\pm 0.003$ dex, $\Delta f_{\mathrm{AGN}}=-0.010\pm0.033$ dex and $\Delta L_{\mathrm{AGN}}=0.002\pm0.025$ dex. After further visual purification of the merger sample, we find $\Delta \mathrm{SFR}=-0.033\pm0.014$ dex, $\Delta f_{\mathrm{AGN}}=-0.024\pm0.170$ dex, and $\Delta L_{\mathrm{AGN}}=0.019\pm0.129$ dex for pairs, and $\Delta \mathrm{SFR}=-0.057\pm0.024$ dex, $\Delta f_{\mathrm{AGN}}=0.286\pm0.270$ dex, and $\Delta L_{\mathrm{AGN}}=0.329\pm0.195$ dex for postmergers. These numbers suggest secular processes being an important driver for SF and AGN activity, and present a cautionary tale when using longer timescale tracers.

One of the most surprising results of early James Webb Space Telescope (JWST) observations is the discovery of an abundance of red, compact, broad-line objects dubbed "little red dots" (LRDs) at z>4. Their spatial density (∼10^-4-10^-5 cMpc^-3) is 100 times more abundant than UV-selected quasars at those redshift if one extrapolates the quasar luminosity function (QLF) down to the LRD regime. However, whether LRDs dominate black hole accretion at quasar-like luminosities (L_bol≳ 10^45-46 erg s^-1) remains unanswered, as probing the bright end of the LRD luminosity function requires a much larger area than those able to be surveyed by JWST. In this work, we present our search for the brightest LRDs (K<23.7) at 4.5<z<4.9 using wide-area multiwavelength imaging surveys from the near-UV to the infrared bands. With over 15 square degrees of sky coverage, we only identify one single LRD candidate at z_phot≈4.6, which translates into a spatial density of n(M_5100<-23.5)≈10^-8 cMpc^-3 – this is nearly 10 times less abundant than the UV-selected quasars at similar optical luminosity. When combined with the LRD sample identified by JWST at the same redshift range, we find a sharp cutoff in the optical luminosity function at λL_5100≈2.5×10^44 erg s^-1, while the QLF turnover occurs at ≳20 times higher luminosity. We therefore confirm the exclusively low-luminosity nature of LRDs, ruling out that LRDs are the counter parts of quasars. Furthermore, we speculate that, if the shape of the luminosity function holds up, it points to LRDs being powered by low-mass black holes with a narrow range of Eddington-level accretion rates.

Tracking the cold molecular gas contents of galaxies is critical to understand the interplay between star formation and galaxy growth across cosmic time. Observations of the long-wavelength dust continuum, a proxy for the cold gas, are widely used in the high-redshift community because of their ease and efficiency. These measurements rely on the assumption of a molecular gas-to-dust mass ratio, typically taken to be δ _GDR ≈ 100 in massive, metal-rich systems. We present Atacama Large Millimeter/submillimeter Array observations of the 870 μ m dust continuum in a sample of five massive quiescent galaxies at z ∼ 1 with existing detections of CO(2–1). We find surprisingly weak dust emission, falling a factor of ≳0.4–0.8 dex below the typical correlation between CO and continuum luminosity. We interpret this dust deficiency as evidence for unusually high δ _GDR in these galaxies, which we calculate to range from 300 to at least 1200. Our results and other observations from the literature are generally compatible with predictions from the SIMBA cosmological simulation that dust is preferentially destroyed in quiescent galaxies. Ultimately, we conclude that the dust continuum is a highly unreliable tracer of the molecular gas in high-redshift quiescent galaxies. As a consequence, we may know much less about the cold gas contents of this population than previously thought.

The origin of the rest-optical emission of compact, red, high-redshift sources known as little red dots (LRDs) poses a major puzzle. If interpreted as starlight, it would imply that LRDs constitute the densest stellar systems in the Universe. However, alternative models suggest active galactic nuclei (AGN) may instead power the rest-optical continuum. Here, we present JWST/NIRSpec, NIRCam, and MIRI observations from the RUBIES and PRIMER programs of The Cliff: a bright LRD at z = 3.55 with an exceptional Balmer break, twice as strong as that of any high-redshift source previously observed. The spectra also reveal broad hydrogen (H alpha FWHM similar to 1500 km s(-1)) and He I emission, but no significant metal lines. We demonstrate that massive evolved stellar populations cannot explain the observed spectrum, even when considering unusually steep and strong dust attenuation or reasonable variations in the initial mass function. Moreover, the formally best-fit stellar mass and compact size (M-* similar to 10(10.5) M-circle dot, r(e) similar to 40 pc) would imply densities at which near-monthly stellar collisions might lead to significant X-ray emission. We argue that the Balmer break, emission lines, and H alpha absorption line are instead most plausibly explained by a black hole star (BH*) scenario, in which dense gas surrounds a powerful ionising source. In contrast to recently proposed BH* models of dust-reddened AGN, we show that spectral fits in the rest UV to near-infrared favour an intrinsically redder continuum over strong dust reddening. This may point to a super-Eddington accreting massive black hole or, possibly, the presence of (super)massive stars in a nuclear star cluster. The Cliff is the clearest evidence to date that at least some LRDs are not ultra-dense massive galaxies, and are instead powered by a central ionising source embedded in dense, absorbing gas.

Internal gas inflows driven by galaxy mergers are considered to enhance star formation rates (SFRs), fuel supermassive black hole growth, and stimulate active galactic nuclei (AGNs). However, quantifying these phenomena remains a challenge, due to difficulties both in classifying mergers and in quantifying galaxy and AGN properties. We quantitatively examine the merger–SFR–AGN connection using Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) galaxies using novel methods for both galaxy classification and property measurements. Mergers in HSC-SSP observational images are identified through fine-tuning Zoobot, a pretrained deep representation learning model, using images and labels based on the Galaxy Cruise project. We use galaxy and AGN properties that were produced by fitting Galaxy and Mass Assembly spectra using the spectral energy distribution fitting code P ro S pect , which fits panchromatically across the far-ultraviolet through far-infrared wavelengths and obtains galaxy and AGN properties simultaneously. Small differences are seen in SFR and AGN activity between mergers and controls, with ΔSFR = −0.009 ± 0.003 dex, Δ f _AGN = −0.010 ± 0.033 dex, and Δ L _AGN = 0.002 ± 0.025 dex. After further visual purification of the merger sample, we find ΔSFR = −0.033 ± 0.014 dex, Δ f _AGN = −0.024 ± 0.170 dex, and Δ L _AGN = 0.019 ± 0.129 dex for pairs, and ΔSFR = −0.057 ± 0.024 dex, Δ f _AGN = 0.286 ± 0.270 dex, and Δ L _AGN = 0.329 ± 0.195 dex for postmergers. These numbers suggest secular processes being an important driver for star formation and AGN activity, and present a cautionary tale when using longer-timescale tracers.

JWST has revealed an abundance of compact, red objects at z ≈ 5–8 dubbed “little red dots” (LRDs), whose SEDs display a faint blue UV continuum followed by a steep rise in the optical. Despite extensive study of their characteristic V-shaped SEDs, the nature of LRDs remains unknown. We present a new analysis of the NIRSpec/PRISM spectrum of A2744-QSO1, a triply imaged LRD at z = 7.04 from the UNCOVER survey. The spectrum shows a strong Balmer break and broad Balmer emission lines, both of which are difficult to explain with models invoking exclusively AGN or stellar contributions. Our fiducial model decomposes the spectrum into a post-starburst galaxy dominating the UV-optical continuum and a reddened AGN being subdominant at all wavelengths and contributing at a level of ∼20%. However, this model infers a stellar mass of M _⋆ ≈ 4 × 10 ^9 M _⊙ within a radius of r _e < 30 pc, driving its central density to the highest among observations to date. This high central density could be explained if A2744-QSO1 is the early-forming core of a modern-day massive elliptical galaxy that later puffed up via the inside-out growth channel. The models also necessitate an unusually steep dust extinction law to preserve the strong break strength, though this steepness may be explained by a deficit of large dust grains. It is also probable that these challenges reflect our ignorance of A2744-QSO1's true nature. Future variability and reverberation mapping studies could help disentangle the galaxy and AGN contribution to the continuum, and deeper redder observations could also unveil the dust properties in LRDs.

With its sensitivity in the rest-frame optical, the James Webb Space Telescope (JWST) has uncovered active galactic nuclei (AGN), comprising both intrinsically faint and heavily reddened sources, well into the first billion years of the Universe, at $z \sim 4-11$. In this work, we revisit the AGN contribution to reionization given the high number densities associated with these objects. We use the DELPHI semi-analytic model, base-lined against the latest high-redshift datasets from the JWST and the Atacama Large millimetre Array (ALMA) to model early star forming galaxies and AGN. We calculate the escape fractions of ionizing radiation from both star formation and AGN and include the impact of reionization feeback in suppressing the baryonic content of low-mass galaxies in ionized regions. This model is validated against the key observables for star forming galaxy, AGN and reionization. In our {\it fiducial} model, reionization reaches its mid-point at $z \sim 6.9$ and ends by $z \sim 5.9$. Low stellar mass ($M_*\leq 10^9M_\odot$) star forming galaxies are found to be the key drivers of the reionization process, providing about $77\%$ of the total photon budget. Despite their high numbers, high accretion rates and higher escape fractions compared to star forming galaxies at $z \sim 5$, AGN only provide about $23\%$ of the total reionization budget which is dominated by black holes in high stellar mass systems (with $M_* \geq 10^9M_\odot$). This is because AGN number densities become relevant only at $z \leq 7$ - as a result, AGN contribute as much as galaxies as late as $z \sim 6.2$, when reionization is already in its end stages. Finally, we find that even contrasting models of the AGN ionizing photon escape fraction (increasing or decreasing with stellar mass) do not qualitatively change our results.

Understanding the dark matter (DM) halo environment in which galaxies that host active galactic nuclei (AGN) reside is a window into the nature of supermassive black hole (SMBH) accretion. We apply halo occupation distribution (HOD) modeling tools to interpret the angular cross-correlation functions between 1.5×10^6 luminous red galaxies (LRGs) and our ∼28,500 Hyper Suprime-Cam + Wide-field Infrared Survey Explorer-selected (and L_6 μm-limited) AGN to infer the halo properties of distinct quasar samples at physical scales s>0.1 Mpc, for z∈0.7-1.0. We find that Type I (unobscured) and Type II (obscured) AGN cluster differently, both on small and large physical scales. The derived HODs imply that Type I AGN reside, on average, in substantially (∼3×) more massive halos (M_h ∼ 10^13.4 M_⊙) than Type II AGN (M_h ∼ 10^12.9 M_⊙) at >5σ significance. While Type II AGN show one-halo correlations similar to that of galaxies of their average halo mass, the Type I AGN intra-halo clustering signal is significantly shallower. We interpret this observation with HOD methods and find Type I AGN are significantly less likely (f_sat∼0.05^+1_-0.05%) to be found in satellite galaxies than Type II AGN. We find reddened + obscured AGN to have typical satellite fractions for their inferred average halo mass (∼10^13 M_⊙), with f_sat∼ 20^+10_-5%. Taken together, these results pose a significant challenge to the strict unified AGN morphological model, and instead suggest that a quasar's spectral class is strongly correlated with its host galaxy's dark matter halo environment. These intriguing results have provided a more complex picture of the SMBH – DM halo connection, and motivate future analyses of the intrinsic galaxy and accretion properties of AGN.

JWST has revealed diverse new populations of high-redshift ( z ∼ 4–11) active galactic nuclei (AGNs) and extreme star-forming galaxies that challenge current photoionization models. In this paper, we use rest-frame UV emission-line diagnostics to identify AGN candidates and other exceptional ionizing sources, complementing previous studies predominantly focused on broad-line AGNs. From a parent sample of 205 z _spec > 3 UNCOVER galaxies with NIRSpec/PRISM follow-up, we identify 12 galaxies with C IV , He II , and/or C III ] emission. Three of these galaxies also exhibit clear N III ] and/or N IV ] lines. Leveraging the combined rest-optical and UV coverage of PRISM, we limit the emission-line model space using the sample’s [O III ]/H β distribution, significantly decreasing the overlap between AGN and star formation models in the UV diagnostics. We then find that the five He II emitters are the strongest AGN candidates, with further support from two [Ne v ] detections and one X-ray detection from Chandra. Our Balmer line fits also reveal one new broad-line AGN at z = 6.87. We cannot robustly quantify the AGN fraction in this sample, but we note that close to 20% of M _* > 2 × 10 ^9 M _⊙ parent sample galaxies are AGN candidates. The lower-mass line emitters, which are consistent with both AGN and star-forming photoionization models, have more compact sizes and higher specific star formation rates than the parent sample. Higher-resolution and deeper data on these UV line emitters should provide much stronger constraints on the obscured AGN fraction at z > 3.

Atacama Large Millimeter/submillimeter Array observations have shown that candidate "post-starburst" galaxies (PSBs) at z ∼ 0.6 can retain significant molecular gas reservoirs. These results would imply that—unlike many model predictions—galaxies can shut down their star formation before their cold gas reservoirs are depleted. However, these studies inferred star formation rates (SFRs) either from [O ii] line fluxes or from spectral energy distribution (SED) modeling and could have missed large dust-obscured contributions to the SFRs. In this study, we present Keck/NIRES observations of 13 massive (M* ≳ 1011 M⊙) PSBs, which allow us to estimate Hα SFRs in these gas-rich PSBs. We confirm the previously inferred low SFRs for the majority of the sample: 11/13 targets show clear Hα absorption, with minimal infilling indicating dust-corrected SFRs of <4.1 M⊙ yr−1. These SFRs are notably low given the large H2 reservoirs (∼(1–5) × 1010 M⊙) present in 5/13 of these galaxies, placing them significantly offset from star-forming galaxies on the Kennicutt–Schmidt relation for star-forming galaxies. The [N ii]/Hα ratios of all 13 PSBs imply contributions from non-star-forming ionization mechanisms (e.g., active galactic nuclei, shocks, or hot evolved stars) to their Hα emission, suggesting that even these low ongoing SFRs may be overestimated. These low Hα SFRs, dust corrected using Av estimates from SED fitting, confirm that these galaxies are very likely quiescent and, thus, that galaxies can quench before their cold gas reservoirs are fully depleted.

The physical processes that led to the formation of billion solar mass black holes within the first 700 million years of cosmic time remain a puzzle. Several theoretical scenarios have been proposed to seed and rapidly grow black holes, but direct observations of these mechanisms remain elusive. Here we present a source 660 million years after the Big Bang that displays singular properties: among the largest Hydrogen Balmer breaks reported at any redshift, broad multi-peaked Hβ emission, and Balmer line absorption in multiple transitions. We model this source as a "black hole star" (BH*) where the Balmer break and absorption features are a result of extremely dense, turbulent gas forming a dust-free "atmosphere" around a supermassive black hole. This source may provide evidence of an early black hole embedded in dense gas – a theoretical configuration proposed to rapidly grow black holes via super-Eddington accretion. Radiation from the BH* appears to dominate almost all observed light, leaving limited room for contribution from its host galaxy. We demonstrate that the recently discovered "Little Red Dots" (LRDs) with perplexing spectral energy distributions can be explained as BH*s embedded in relatively brighter host galaxies. This source provides evidence that black hole masses in the LRDs may be over-estimated by orders of magnitude – the BH* is effectively dust-free contrary to the steep dust corrections applied while modeling LRDs, and the physics that gives rise to the complex line shapes and luminosities may deviate from assumptions underlying standard scaling relations.

ALMA observations have shown that candidate "post-starburst" galaxies (PSBs) at z∼0.6 can retain significant molecular gas reservoirs. These results would imply that – unlike many model predictions – galaxies can shut down their star formation before their cold gas reservoirs are depleted. However, these studies inferred star formation rates (SFRs) either from [O II] line fluxes or from spectral energy distribution modeling, and could have missed large dust-obscured contributions to the SFRs. In this study, we present Keck/NIRES observations of 13 massive (M_*≳× 10^11 M_⊙) PSBs, which allow us to estimate Hα SFRs in these gas-rich post-starburst galaxies. We confirm the previously inferred low SFRs for the majority of the sample: 11/13 targets show clear Hα absorption, with minimal infilling indicating dust-corrected SFRs of <4.1 M_⊙ yr^-1. These SFRs are notably low given the large H_2 reservoirs (∼ 1-5 × 10^10 M_⊙) present in 5/13 of these galaxies, placing them significantly offset from star-forming galaxies on the Kennicutt-Schmidt relation for star-forming galaxies. The [N II]/Hα ratios of all 13 PSBs imply contributions from non-star-forming ionization mechanisms (e.g., AGN, shocks, or hot evolved stars) to their Hα emission, suggesting that even these low ongoing SFRs may be overestimated. These low Hα SFRs, dust-corrected using A_v estimates from SED fitting, confirm that these galaxies are very likely quiescent and, thus, that galaxies can quench before their cold gas reservoirs are fully depleted.