Akio K. Inoue

We measured the Concentration (C) index of H α and CO (J = 2-1) in 17 nearby star-forming galaxies from the PHANGS survey. We have found four barred spiral galaxies with a C(H α)/C(CO) ratio of ~ 0.3-0.4, while the other 13 galaxies exhibit ratios of ~ 1 (ranging from 0.7 to 1.3). All four barred galaxies with low ratios host active galactic nuclei (AGNs), consistent with a scenario in which star formation is suppressed by mechanical and radiative feedback from the AGN. Therefore, negative feedback may be effective in these four barred galaxies even when AGN activity is relatively weak. The formation of bar structures causes molecular gas to collect in the central region, leading to starburst activity. However, after the starburst, the remaining gas becomes inefficient for star formation rapidly due to AGN feedback. This can mean the quenching process occurs more rapidly in AGN-barred galaxies. Furthermore, since gas remains in the central region, AGN activity is likely to continue. These quenching processes are a unique mechanism found in barred spiral galaxies and are essential to understanding galaxy evolution.

We present an analysis on the kinematics and physical properties of the ionised gas in the lensed galaxy RXCJ2248-ID at z = 6.105 based on high-resolution JWST NIRSpec/IFU data. This source is a nitrogen-rich high- z galaxy showing a compact morphological structure and high star formation and stellar surface densities. The magnification factor of the observed image of the source (ID3, μ = 5.3) along with the rich dataset available, including NIRSpec and ALMA spectroscopy, makes this target an ideal benchmark to study the physical properties of nitrogen-rich galaxies. In this work, we use the large number of optical lines detected at a high signal-to-noise (S/N) in our NIRSpec high-resolution ( R = 2700) integral field spectra to analyse potential differences in kinematics, dust distribution, and electron temperature and density. In addition, we combine our data with available ALMA observations to derive the optical-to-far-IR [O III ] λ 5008/[O III ] 88 μm ratio in order to estimate the electron density of the O ⁺⁺ regions. Our analysis revealed a high electron temperature ( T _e ∼ 30 000 K) in the ionised gas independent of the ionisation level. We measured a wide range in the electron densities of the ionised interstelllar medium (ISM) from our [O III ] λ 5008/[O III ] 88 μm and [Ar IV ] λ 4713/[Ar IV ] λ 4742 ratios (log( n _e [cm ⁻³ ]) ∼ 2.7−3.8) and previous values (i.e. 4.8 < log( n _e [cm ⁻³ ]) < 5.5) based on high-ionisation rest-UV emission lines. The ionised gas appears to be clumpy with a low filling factor ranging from about 10% to 0.2% for the low- and high-density clouds. In addition, we observed a very complex ISM kinematic structure traced by the [O III ] λ 5008 and H α lines. Concretely, we derived the presence of two distinct broad and very broad components (FWHM ∼ 210−250 and ∼1000−1500 km s ⁻¹ ) in addition to the systemic component (FWHM ∼ 60−70 km s ⁻¹ ). These broad components are heavily extinct ( A _V ∼ 1.5 and 2.5, respectively), based on their Balmer decrements, while the gas associated with the narrow component is consistent with no extinction. The maximal velocities of these outflows (∼115−500 km s ⁻¹ ) are such that a fraction of the total outflowing gas (0.16−2.1 × 10 ⁷ M _⊙ ) could escape into the intergalactic medium. The rest of the gas will fall back to the central regions, remaining available for additional star formation episodes. The presence of dusty outflows and a clumpy (i.e. low filling factor) ISM give support to the attenuation-free scenario proposed to explain the high- z UV-bright compact galaxies such as RXCJ2248-ID. On the other hand, the high densities in the ISM together with the high sta formation rate surface brightness and the amount of returning outflowing mass give support to the feedback-free starburst scenario.

Understanding dust attenuation in galaxies at both integrated and spatially resolved scales is fundamental for accurately determining the physical properties of galaxies. Recent high-spatial-resolution observations with the Atacama Large Millimeter/submillimeter Array and James Webb Space Telescope enable investigations of spatially resolved properties in high-redshift galaxies ( z ≳ 6), but spatial variations in dust observables remain poorly constrained. We use cosmological zoom-in simulations combined with postprocessing dust radiative transfer calculations for 376 clumpy galaxies at z = 6–9 with stellar masses of M _* ≳ 10 ⁹ M _⊙ . For each system, we investigate dust attenuation and reemission properties for three components: system integrated, individual clumps, and diffuse regions. We find that system-integrated attenuation curves are grayer than the Calzetti curve, even when assuming Milky Way– or Small Magellanic Cloud–type dust. Attenuation curves of individual clumps are even grayer, while diffuse regions exhibit steeper curves owing to enhanced scattering in optically thin environments. Since the effects of optical depth and dust–star geometry are intrinsically degenerate in attenuation curves, we introduce a toy model based on the infrared excess (IRX)–Δ β plane, where Δ β denotes the difference between attenuated and intrinsic ultraviolet slopes. Applying this framework, we find that clumps have dust column densities approximately 1 order of magnitude higher than system-integrated values and exhibit cospatial or dust-extended geometries. In contrast, system-integrated attenuation reflects star-extended geometries driven by contributions from optically thin diffuse regions. We apply this framework to REBELS-IFU galaxies at z ∼ 7 and find good agreement with our simulation predictions.

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.

Our understanding of the physical mechanisms and environments conducive to the escape of Lyman continuum (LyC) radiation within the first 2 Gyr of cosmic history remains limited. Here, we present a detailed analysis of JWST NIRSpec medium-resolution IFU observations of two LyC-leaker candidates, LACES-94460 and LACES-104037 at z = 3.1, selected from deep Hubble Space Telescope/WFC3 F336W imaging and supported by ground-based spectroscopy. We first rule out LACES-94460 as a genuine LyC leaker, demonstrating that its apparent F336W signal originates from a nearby low-redshift interloper at z = 1.6, unambiguously identified through IFU spectroscopy. In contrast, for LACES-104037, we spectroscopically confirm bona fide LyC emission arising from a tidal-tail structure during the early stage of a galaxy merger, dubbed LACES104037-LyC. LACES104037-LyC exhibits extremely low rest-frame optical emission-line equivalent widths together with an exceptionally strong LyC flux. Within a picket-fence model framework, we reproduce its observed spectral and photometric properties with a young stellar population of age ∼5 Myr and an LyC escape fraction of f_esc ∼ 99%. Our identification and detailed modeling of LACES104037-LyC provide one of the first compelling observational demonstrations for merger-driven LyC escape, indicating that galaxy mergers may represent an important and previously underappreciated contributor to the ionizing photon budget relevant for cosmic reionization. Furthermore, our analysis highlights the critical role of subkiloparsec resolution spectroscopy in securely identifying LyC leakers, removing contamination from closely projected low-redshift interlopers, and pinpointing the physical regions responsible for LyC leakage.

We present a study of 27 very UV-bright (−22.0 ≲ M _UV ≲ −24.4) star-forming galaxies at z ∼ 6 identified in the Subaru High- z Exploration of Low-Luminosity Quasars (SHELLQs) survey. Stacking their rest-frame UV spectra revealed a prominent N V λ 1240 P Cygni feature, consistent with very young (∼6 Myr) stellar populations dominated by massive and hot stars. Ultraviolet-bright galaxies in the reionization epoch are thus powerful and efficient ionizing sources, with an average ionizing photon production efficiency of log( ξ _ion /Hz erg ⁻¹ ) = 25.54 ^+0.09 _−0.12 . For one representative source, J0217–0208 at z = 6.204 ( M _UV = −23.4), we analyzed available JWST/NIRCam and NIRSpec observations. Its spectral energy distribution indicates a young (∼5 Myr) starburst with a stellar mass of 10 ⁹ M _⊙ and a high specific star formation rate (∼100 Gyr ⁻¹ ). Together with its very compact NIRCam-measured size ( r _eff ≃ 260 pc), this corresponds to stellar mass and star formation rate surface densities approximately one hundred times higher than those of typical galaxies at comparable redshifts. NIRSpec spectroscopy further revealed strong nebular emission, for which we derived a high electron density ( n _e ≃ 10 ³ cm ⁻³ ), a metallicity of 12 + log(O/H) = 8.20 ± 0.11 (from the direct method), and a super-solar N/O ratio (log(N/O) ≃ −0.30). Furthermore, J0217–0208 shows broad components in several rest-optical emission lines, indicating powerful ionized outflows. From the Balmer decrement, these outflows appear to be heavily obscured ( E ( B − V ) _out ≃ 0.6), in contrast to the nearly dust-free stellar continuum ( E ( B − V ) _★ = 0.01 ± 0.01) obtained from its steep UV slope, β _UV ≃ −2.6. Combined with ALMA detections of a massive ( M _dust ≃ 2 × 10 ⁸ M _⊙ ), extended (∼1.4 kpc), and cold ( T _dust ≃ 25 K) dust reservoir, these findings point to dusty feedback-driven outflows carrying and pushing dust well beyond the stellar core and likely boosting the observed UV luminosity. Taken together, our results suggest that UV-bright galaxies at high redshift represent short-lived but extreme phases of rapid stellar mass growth, efficient ionizing photon production, and strong feedback. The extreme properties of J0217–0208, such as a supersolar N/O, a steep UV slope, a compact size, and very high surface densities, closely mirror those of the brightest galaxies at z > 10, suggesting a shared evolutionary pathway.

One of the major conundrums in contemporary extragalactic astrophysics is the apparent overabundance of a remarkable population of UV-bright galaxies at redshifts z≳ 9. We analysed galaxies spectroscopically observed by PRISM and confirmed to lie at z>9, with a sufficient signal-to-noise to carefully model their rest-frame UV-to-optical continua and line emission. In particular, we modelled the damped Lyman-α (Lyα) absorption (DLA) features of each galaxy to place observational constraints on the gas assembly of neutral atomic hydrogen ( onto the galaxy halos at the onset of cosmic reionisation. Based on the derived column densities and star formation rate (SFR) surface densities, we show that all galaxies are highly efficient at forming stars on rapid ∼ 10-100,Myr depletion timescales, greatly in excess compared to the canonical local Universe Kennicutt-Schmidt (KS) relation and predictions from state-of-the-art galaxy formation simulations. The dense gas appears to also drive the offset from the fundamental-metallicity relation (FMR) of these galaxies though its dust-to-gas (DTG) ratio is seemingly consistent with values derived for local galaxies except for the lowest metallicity sight lines. Our results provide the first robust observational constraints on the impact of pristine gas on early galaxy assembly, and they imply that a combination of highly efficient star formation and low dust obscuration can likely explain the UV brightness of galaxies at cosmic dawn.

We present results of new observations of [O i ] 145 μ m and [N ii ] 205 μ m emission lines from four star-forming galaxies at redshifts between z = 6.58 and 7.68 that have previous detections of [C ii ] 158 μ m and dust continua. Using the Atacama Large Millimeter/submillimeter Array, we successfully detect [O i ] 145 μ m emission from all targets at >4 σ significance. However, [N ii ] 205 μ m emission is undetected in all galaxies (signal-to-noise ratio < 3.5 σ ) except for a tentative detection from A1689-zD1. From the observed high [C ii ]/[N ii ] emission line ratios (≳20−80), we find that most of the [C ii ] 158 μ m emission arises from neutral gas regions (3 σ lower limits of ≳74%−96%). From [O i ] 145 μ m, [C ii ] 158 μ m lines, and IR luminosities, we estimate the neutral gas densities of n _H = 10 ^3.5 –10 ⁶ cm ⁻³ and the far-UV (FUV) radiation strengths of G ₀ ∼ 10 ^2.5 –10 ³ . While the neutral gas densities are similar to those of high-redshift starburst galaxies, the FUV strengths are lower compared to both local and high-redshift starbursts. Finally, we estimate atomic hydrogen masses using [O i ] 145 μ m emission lines and the oxygen abundances measured from recent JWST observations. We find gas mass ratios of f _gas ∼ 0.3–0.8, which are similar to earlier studies using [C ii ] 158 μ m. Starting from this pilot observation, future large [O i ] 145 μ m emission line surveys will provide us with currently little-known neutral gas properties of star-forming galaxies in the early Universe.