Luis Colina

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.

We present a panchromatic optical-millimeter characterization of GNz7q, a recently identified X-ray-weak, rapidly growing red quasar embedded within a dusty starburst galaxy at z = 7.1899, using the full suite of JWST/NIRCam, NIRSpec, Mid-Infrared Instrument (MIRI), and archival NOEMA observations. Our deep NIRSpec/G395M spectroscopy reveals unambiguous broad Balmer emission (FWHM = 2221 ± 20 km s ⁻¹ ), confirming a super-Eddington accreting black hole (BH) ( λ _Edd = 2.7 ± 0.4) with a mass of log ( M BH / M ⊙ ) = 7.55 ± 0.34 , using accretion-rate-corrected BH mass estimators. After subtracting the point source, we robustly detect stellar emission from the host galaxy across multiple NIRCam and MIRI filters. Our joint morphological-spectral analysis yields a stellar mass of log ( M * / M ⊙ ) = 10.5 ± 0.4 and an intense star formation rate of SFR = 330 ± 97 M _⊙ yr ⁻¹ , confirming the host as a massive, dusty starburst galaxy. We find that GNz7q lies on the local M _BH – M _* relation ( M _BH / M _* ≃ 0.001) and is well positioned to evolve into the locus of massive Sloan Digital Sky Survey (SDSS) quasars with log ( M BH / M ⊙ ) ≈ 9 and M _* ≈ 10 ¹¹ M _⊙ at z ∼ 6, owing to its remarkably rapid growth in both the BH and its host galaxy. This stands in stark contrast to many recently reported JWST active galactic nucleus populations at similar redshifts, including the little red dots, whose weak or undetected star formation makes it difficult for them to grow into the massive galaxies hosting SDSS-like quasars. These results suggest that GNz7q marks a rare, pivotal phase of early BH–galaxy coevolution, plausibly providing a crucial direct pathway to the supermassive BH systems within the first billion years of the Universe.

The classical picture for the formation of stellar bars—key dynamical drivers of the evolution of galaxies—is through secular evolution of instability in gas-poor, stellar-dominated disks. The detection with the James Webb Space Telescope of stellar bars and spiral arms in galaxies at early cosmic times has thus challenged ΛCDM-based expectations, which recent studies reconcile by suggesting that these galaxies are baryon-dominated and have already consumed most of their gas. Yet, a paradox arises, as early galaxies are expected to be increasingly rich in gas, which is generally considered to prevent or slow down stellar bar formation. Here, we show the detection of a stellar bar in GN20, a gas-rich star-forming disk galaxy at a redshift of z = 4.055, only 1.5 Gyr after the Big Bang. Simultaneous observations of the stars, gas, and dust reveal that GN20 is indeed baryon-dominated (over dark matter; 72% ± 34%), but the baryonic mass is largely in the form of gas (74% ± 25%). This discovery demonstrates that gas-rich disks do support rapid stellar bar formation in the early Universe, motivating a new theoretical perspective on bar formation in gas-rich systems, and providing a potential new mechanism for very early galaxy assembly and quenching.

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.

Context. Tracing the origin of the gas emission lines in galaxies can prove challenging in certain cases. Buried active galactic nuclei (AGNs) and obscured young stellar clusters pose significant obstacles with respect to traditional optical diagnostic diagrams. Therefore, developing new tools to trace the excitation sources across the spectrum is a necessary effort for the advancement of the field. Aims. Our goal is to explore the full spectral range of the JWST–NIRSpec data, searching for alternative diagnostic diagrams in the less explored near-infrared (NIR) and to investigate the nature of the ionizing and heating source. Methods. We analyzed the high-resolution spectra of the circumnuclear regions of nine local ( z < 0.1) U/LIRGS, investigating potential emission-line ratios for tracing the excitation mechanisms acting on the line-emitting gas. We investigated these objects using the well-established [Fe II ] 1.2570 μm/Pa β versus H ₂ 1–0 S(1)/Br γ diagram and attempted to correlate its classifications with other emission features across the spectrum. We then compared the empirical classifications with CLOUDY photoionization models to evaluate how accurately the data can be reproduced. Finally, we compared the line widths at 80% of the total flux ( W ₈₀ ) of selected emission lines with the corresponding gas excitation mechanisms. Results. We propose two line-excitation diagnostic diagrams based on [C I ] 0.9852 μm/Pa γ and H ₂ 1–0 O(5)/PAH 3.3 μm ratio, which we found to directly correlate with the hardness of the radiation field and, therefore, with the gas excitation mechanisms. Both the empirical [Fe II ] 1.2570 μm/Pa β versus H ₂ 1–0 S(1)/Br γ diagram and our proposed [C I ] 0.9852 μm/Pa γ versus H ₂ 1–0 S(1)/Br γ diagnostic diagram are well reproduced by the photoionization models. In addition, the line-kinematics analysis shows that the W ₈₀ values of regions excited by star formation are, on average, slightly lower than those of AGN-excited regions, while shock-excited regions display distinctively higher W ₈₀ values compared to the other two groups. Our JWST–NIRSpec results reinforce reports in previous studies indicating that the H ₂ emission in the central regions of AGN hosts is complex and likely produced by multiple excitation mechanisms.

Jet–cloud interactions are a key manifestation of active galactic nucleus (AGN) feedback on nuclear scales, which is distinct from the large-scale radio-mode feedback that suppresses gas cooling in galaxy halos. On these smaller scales, radio jets can inject energy and momentum into the interstellar medium (ISM), shaping the physical and kinematic properties of the nuclear and circumnuclear regions of galaxies. Using JWST MIRI/MRS observations of seven nearby radio-loud AGNs (3C 293, 3C 305, Centaurus A, Cygnus A, IC 5063, NGC 1052, and M 87), we investigated jet-driven turbulence in both the warm molecular and ionized gas phases. By combining spatially resolved H ₂ /polycyclic aromatic hydrocarbon flux ratios with diagnostic line ratios of the ionized gas, we constrained the dominant H ₂ excitation processes and assessed the impact of radio jet–ISM interactions on the multiphase gas. We find that radio jets drive increased turbulence in both molecular and ionized (traced by [Fe II ], [Ne II ], and [Ne III ] lines) gas, not only along but also perpendicular to the jet axis, indicating that jet–ISM interactions extend beyond the collimated jet channel and affect the nuclear environment. Strong correlations between the H ₂ /polycyclic aromatic hydrocarbon ratio, the H ₂ excitation temperature, and shock-sensitive ionized-gas tracers indicate that jet-driven shocks dominate the excitation of the H ₂ rotational lines in most sources. These results indicate that radio jets are a key driver of multiphase ISM kinematics and excitation in nearby radio-loud galaxies.

Context. Supermassive black holes power active galactic nuclei (AGNs), injecting energy that may regulate accretion and shapes host galaxies. High-resolution observations of circumnuclear gas and dust are essential to understanding these processes. Aims. We aim to investigate the morphology, excitation, and kinematics of warm molecular hydrogen (H_2) in the inner circumnuclear disk of Centaurus A, the nearest radio galaxy. Methods. We present JWST/MIRI MRS integral-field spectroscopy of the central 170 Warm H_2 shows a complex morphology, dominating the central region where CO emission is weak or undetected. Low-excitation ̋mol lines trace an inhomogeneous ring with a 20-pc radius cavity aligned with the jet's near side, suggesting that the jet affects the morphology of the molecular disk. Higher excitation lines form a filamentary structure around the AGN. Kinematics are primarily rotational with an S-shaped distortion, indicating noncircular motions or a warped disk. A coherent, low-dispersion (∼70 100 pc2$ at 0.3"--0.7" (5--12 pc) resolution, focusing on pure rotational H_2 lines. The spectra exhibit a strong nuclear continuum, and bright H$_2 lines from S(1) to S(8), including the first S(8) detection in Centaurus A. The lines are optically thin in the nucleus, enabling maps of temperature, column density, and ortho-to-para ratio from spaxel-level excitation diagram fitting. Results. -1 $) streamer spirals inward. A power-law temperature distribution yields a warm (100--2000 K) H_2 mass of $(5.6 ± 1.4) , and sub-equilibrium ortho-to-para ratios (1.6--2.4). M_⊙ and a dynamical mass of 5 / M_⊙ within 100 pc. Shock excitation is supported by enhanced H_2/continuum and H$_2/PAH ratios, elevated Ne iii Ne ii Conclusions. Turbulent dissipation can balance the observed H_2 cooling and likely dominates heating beyond 30 pc. In the inner 100 pc of Centaurus A, AGN feeding and feedback are linked: shocks excite H_2, regulate the gas temperature, and prevent cooling below 100 K, explaining the weak CO emission and lack of a massive outflow. These shocks may drive angular-momentum loss and help fuel the nucleus.

We analyze two dusty star-forming galaxies at z = 6.6. These galaxies are selected from the ASPIRE survey, a JWST Cycle 1 medium program, and the Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 9 large program targeting 25 quasars and their environments at z ≃ 6.5–6.8. These galaxies are identified as companions to UV-luminous quasars and robustly detected in ALMA continuum and [C ii ] emission, yet they are extraordinarily faint at the NIRCam wavelengths (down to >28.0 AB mag in the F356W band). They are more obscured than galaxies like Arp220 ( A _V up to ∼7.5 mag), and thus we refer to them as “NIRCam-dark” starburst galaxies (star formation rate ≃80–250 M _⊙ yr ⁻¹ ). Such galaxies are typically missed by (sub)-millimeter blank-field surveys. From the star formation history (SFH), we show that the NIRCam-dark galaxies are viable progenitors of massive quiescent galaxies at z ≳ 4 and descendants of UV-luminous galaxies at z > 10. Although it is hard to constrain their number density from a quasar survey, we conclude that NIRCam-dark galaxies can be as abundant as n ∼ 10 ^−5.5 Mpc ⁻³ assuming a light halo occupation model. If true, this would equal to ∼30% of the number densities of both the quiescent galaxies at z ≳ 4 and UV-luminous galaxies at z > 10. We further predict that analogs at z ∼ 8 should exist according to the SFH of early massive quiescent galaxies. However, they may fall below the current detection limits of wide JWST and ALMA surveys, and thus remain “JWST-dark.” To fully trace the evolution of massive galaxies and dust-obscured cosmic star formation at z ≳ 8, wide-field JWST/NIRCam imaging and slitless spectroscopic surveys of early protoclusters are essential.