Carlos De Breuck

High-redshift radio galaxies (HzRGs) are among the most powerful radio sources, and are associated with the most massive galaxies and dense environments at redshifts z ≳ 1. They are ideal laboratories for studying how active galactic nucleus (AGN) events can shape the evolution of galaxies, as intense radiation, jets, and star formation can be observed simultaneously in these galaxies. We present JWST/NIRSpec integral field spectroscopy (∼1.6 kpc spatial resolution) of the 4C +03.24 system, a powerful HzRG at z ∼ 3.5 with a bolometric luminosity of ∼ 10 ^47.6 erg s ⁻¹ . We identified kinematically disturbed regions in the warm (∼10 ⁴ K) ionized gas by decomposing the emission-line spectra into multiple Gaussian components, which is crucial to avoid overestimating the outflow properties. The outflow power peaks at ∼2 kpc away from the nucleus, with a corresponding low kinetic coupling efficiency of ∼ 8 ₋₅ ⁺⁷ × 10 ⁻³ %. A combined analysis of the rest-frame optical and ultraviolet (from VLT/MUSE and HST imaging) continua revealed an extended emission (spanning ∼14 kpc), which we interpret as partially tracing star-forming regions. With a clearly delineated bipolar morphology, we show that the AGN photoionization dominates the ionization of the interstellar medium along the radio jet axis. The [C II ] λ 158µm emission gap in this region might be direct evidence of negative AGN feedback. We also discuss a possible scenario where 4C +03.24 could be situated in an overdense environment experiencing multiple galaxy interactions and the possibility of jet-induced star-formation.

Context . The CarbON [CII] line in post-rEionisation and ReionisaTiOn epoch (CONCERTO) instrument was a low-resolution mapping Fourier-transform spectrometer based on lumped-element kinetic inductance detector (LEKID) technology that operated at 130-310 GHz. It was installed on the 12-meter APEX telescope in Chile in April 2021 and operated until December 2022. CONCERTO’s main science goal is to constrain the [CII] line fluctuations at high redshift. To reach this goal, CONCERTO observed 1.4 deg ² in the COSMOS field. Aims . To ensure accurate calibration of the data, we developed a forward model capable of simulating the spectral response and the corresponding interferograms for each scan of observation in the COSMOS field. We present the modelling approach that enabled us to reproduce the expected instrument outputs under controlled input conditions and that provided a framework for the different calibration steps, including the absolute brightness calibration of the spectra. Methods . We constructed a dedicated analysis pipeline to characterise the raw interferometric data (interferograms) obtained under a broad range of atmospheric conditions at APEX. Using the forward model, we measured the interferogram alignment with the optical path difference (zero path difference) and the relative response of each KID (flatfield). Together, these elements enabled us to characterise the instrument’s spectral brightness calibration reliably. Results . We demonstrate that the zero path difference systematically varies with elevation and across detectors, with variations that are consistent with small optical misalignments and elevation-dependent mechanical effects in the optical structure. The full measurement of these variations allowed us to construct a data base that is used to determine the zero path difference for each measured individual interferogram accurately. The flatfield shows systematic variations with detector position, but is extremely stable with time and atmospheric contribution. The accurate determination of the zero path differences and flatfields allowed us to construct spectral cubes that combine all detectors and all blocks of data. Finally, we present a novel method for calibrating the absolute brightness of these spectral cubes, which is agnostic to the exact knowledge of the bandpasses and directly applicable to extended emission. Conclusions . Our analysis establishes a framework for precise calibration directly from on-sky data. This approach ensures a reliable performance for cosmological and astrophysical applications and can readily be adapted to future Martin-Puplett interferometer-based Fourier-transform spectrometers.

The megahertz spectral-resolution atmospheric radiative-transfer model for ground-based observatories working at millimeter and submillimeter wavelengths has been improved following an observational campaign with the Atacama Pathfinder EXperiment (APEX). Atmospheric spectra were acquired under different diurnal, seasonal, and general weather conditions, followed by a careful analysis of the valid data. The final data set considered in this work consists of 57 spectra that, all combined, cover the 157.3–742.1 GHz frequency range. They span one order of magnitude (~0.35–3.5 mm) in precipitable water vapor columns (PWVC) – which are typical of the site – and were gathered over a two-year period from 21 Oct. 2020 to 5 Sep. 2022. With those data a few weak but detected lines missing from the model were added; the accuracy of line shapes and collision-induced absorption (CIA) was checked along with the assumptions on the vertical profiles of pressure, temperature, water vapor, and minor gases. The resulting atmospheric model parameters were implemented in the Atacama Large Millimeter/Submillimeter Array (ALMA) Telescope Calibration software subsystem (TelCal) and in the Common Astronomy Software Applications package (CASA) Common Software (ACS) libraries.

We report the discovery of strongly absorbed [O I ] 63 μm in a sample of 12 dusty star-forming galaxies (DSFGs) at 4.2 < z < 5.8. This is the first systematic survey of the [O I ] 63 μm fine-structure line at z > 4, targeting a sub-sample of gravitationally lensed DSFGs selected from the South Pole Telescope survey. Using ALMA Bands 9 and 10, we obtained spatially and spectrally resolved observations that probe the interstellar medium on sub-kiloparsec scales. Despite reaching sensitivities one to two orders of magnitude deeper than most previous studies, we detect [O I ] 63 μm in emission in only two sources at low significance, with the remaining galaxies yielding stringent non-detections over the full velocity range covered by robust detections of other far-infrared lines, including [C II ] 158 μm and [N II ] 205 μm. We identify several compact (0.05–0.2″) regions with [O I ] 63 μm absorption against the far-infrared dust continuum, some of which are possibly reaching below rest-frame cosmic-microwave-background (CMB) radiation level. This suggests the presence of low-excitation-temperature (Tex ≤ T _CMB ( z )), low-density gas along those lines of sight. We also detect narrow, spatially localised [O I ] 63 μm emission ’escape channels’ preferentially detected in regions with weak or absent dust continuum emission. We also predict that similar absorption effects may appear in the [C II ] 158 μm line, particularly when concentrating on the regions with the densest foreground material along the line of sight. The [O I ] 63 μm line appears to be strongly affected by the influence of extended star forming regions, with a mix of compact, high-optical-depth [O I ] 63 μm -emitting regions and sub-thermally excited, oxygen-rich molecular clouds dispersed throughout high-redshift starbursts that are capable of absorbing the ground-state line emission. Combined with a comparison to cosmological radiation hydrodynamical simulations, this supports the interpretation that regions with higher gas and dust column densities may lead to weakening an intrinsically strong [O I ] 63 μm line emission. We argue that the high [O I ] 63 μm optical depth is the dominant effect causing the strong absorption, limiting the diagnostic power of this line to trace regions of massive star formation in high-redshift DSFGs.

We present JWST/NIRCam imaging of dusty star-forming galaxies (DSFGs) detected by the Atacama Large Millimetre/submillimetre Array (ALMA) in the Spiderweb protocluster at z = 2.16. We identified 22 DSFGs detected by both ALMA and JWST, ten of which are spectroscopically confirmed as protocluster members. This is the first systematic analysis of a statistical DSFG sample in z ∼ 2 protocluster environments using JWST/NIRCam data. Most of the DSFG members exhibit red colours and reside in the dusty star-forming region of the rest-frame UVJ diagram, indicating strong dust obscuration. The Gini- M ₂₀ diagram suggests that most DSFGs in this protocluster are late-type disks, with a significant fraction displaying clumpy and disturbed rest-frame UV /optical morphologies, but few showing clear merger signatures. The DSFG members exhibit relatively large stellar disks and effective radii with a median stellar mass of log( M / M _⊙ ) = 10.8 ± 0.3, placing them above coeval field DSFGs and typical protocluster galaxies in the size–mass relation at both rest-frame optical and near-infrared wavelengths. These sizes are comparable to those of more evolved field DSFGs at z ∼ 1 − 2, indicating accelerated structural growth in dense environments. Moreover, these DSFG members show a decreasing trend in stellar size from shorter to longer wavelengths, with a moderately steep slope comparable to coeval field DSFGs. These results may support an inside-out growth scenario for protocluster evolution, in which massive galaxies near the centre are more evolved and more strongly affected by active galactic nucleus feedback and environmental effects, for example, ram-pressure stripping. We propose that the cold gas accretion at the protocluster outskirts drives intense star formation and stellar disk growth in ALMA-detected DSFGs, which are expected to evolve into massive elliptical galaxies at later stages.

We perform one of the first spatially resolved studies of warm (>100 K) and cold (10–100 K) molecular gas in the circumgalactic medium (CGM), focusing on the brightest cluster galaxy (BCG) of a cool-core galaxy cluster, MACS 1931−26, at z = 0.35. This galaxy has a massive H ₂ reservoir and a radio-loud active galactic nucleus and is undergoing a starburst event. We present new JWST observations of this system, revealing warm H ₂ gas that is cospatial with the cold molecular gas traced by CO, extending over 30 kpc around the BCG in a tail-like structure reaching into the CGM of this galaxy. Analysis of the mid-infrared pure H ₂ rotational lines H ₂ S(1), H ₂ S(5), and H ₂ S(9) indicate warm gas temperatures of 515.6 ± 0.8 and 535.2 ± 1.9 K in the BCG and tail regions, respectively. We compare the cold gas traced by the CO(3–2) observed with the Atacama Large Millimeter/submillimeter Array to the warm gas traced by JWST. The warm-to-cold molecular gas fraction is comparable in the BCG (1.4% ± 0.2%) and the CGM tail (1.9% ± 0.3%). Our analysis suggests that the dissipation of the kinetic energy of the H ₂ -emitting gas is sufficient to lead to the formation of the CO gas. This observation provides new insights into the molecular gas distribution and its potential role in the interplay between the central galaxy and its circumgalactic environment.