Alastair C. Edge

We present a combined strong and weak gravitational lensing mass model of the massive merging galaxy cluster Abell 2744 ($z = 0.308$). The mass reconstruction combines strong-lensing constraints in the cluster core with weak-lensing measurements derived from deep imaging with the Hubble Space Telescope and the James Webb Space Telescope, enabling a reconstruction of the projected mass distribution from the core to the cluster outskirts. Using the resulting mass map, we identify cluster substructures and construct the subhalo mass function for Abell 2744. To interpret the observed substructure population, we apply identical detection methods to projected mass maps of massive galaxy clusters from the BAryons and HAloes of MAssive Systems (BAHAMAS) simulations. We observe a systematic excess of detected substructures in Abell 2744 compared to BAHAMAS. We interpret this excess as likely reflecting Abell 2744’s exceptionally disturbed dynamical state, characterized by complex ongoing mergers, rather than tension with Lambda cold dark matter or self-interacting dark matter predictions. However, confirming this interpretation will require extending the analysis to a larger sample of clusters spanning a range of dynamical states.

We analyze new high-spectral-resolution Spectromètre Imageur à Transformée de Fourier pour l’Etude en Long et en Large de raies d’Emission (SITELLE) observations ( R = λ /Δ λ = 7000) of the filamentary nebula surrounding NGC 1275, the central galaxy of the Perseus Cluster. We present here analysis of the [S ii ] λ 6716 and [S ii ] λ 6731 emission-line doublet, using its ratio to determine the electron density of the optically emitting filaments. We compare these measurements with electron densities derived from deep Chandra X-ray observations of the intracluster medium (ICM) to determine if any correlations in density can be found. We report the detection of a clear dichotomy between the outer filaments, displaying on average lower [S ii ] emission-line ratios of ∼1.1, and the inner filaments, displaying higher ratios of ∼1.3. These results indicate that most of the gaseous filaments lie close to the low-density threshold for the density measurement of ∼10 ² cm ⁻³ . Using radial profiles, we find that the inner filaments have a roughly constant density, whereas the ICM density decreases with radius. In the outer filaments, we observe hints of local connections between the densities of the ICM and optical filaments, but no clear correlation seems to be observed overall. We also combined these density measurements with cold molecular CO gas observations to derive a relationship between temperature, density, and pressure for the multiphase environment surrounding NGC 1275. Finally, we investigated potential models to explain the observed density measurements and explored similar studies of filamentary nebulae around other central galaxies of cool-core galaxy clusters.

We re-analysed near-infrared and optical spectroscopy from the Subaru, Gemini, and Keck telescopes of the bright gravitational arc seen in the z = 0.62 X-ray cluster eMACS J2229.9-0808. The 22 strongest spectral features we identified uniquely determine the redshift of the galaxy as z = 3.20, as previously reported by Ebeling et al. (2025, MNRAS, 537, 2662), not z = 0.82 as claimed by Wagner & Falco (2026, A&A, 710, A129).

We present new observations from JWST that reveal a striking kiloparsec-wide cavity in the stellar distribution of the central galaxy in the cluster A402. Supporting data from the Hubble Space Telescope (HST) allow us to rule out extinction due to dust as an explanation, and instead, suggest that this is a localized depression in the stellar density field corresponding to ∼2 × 10 ⁹ M _⊙ in missing stars within a volume of 0.5 kpc ³ . On larger scales, both the JWST and HST data show evidence for a 2.2 kpc flattened core in the stellar distribution (on which the smaller-scale cavity is superimposed), which implies the presence of a central ultramassive black hole with M _BH ∼ 5 × 10 ¹⁰ M _⊙ . We report evidence for a mid-IR-bright point source at one edge of the cavity, suggesting that this black hole is actively accreting. MUSE spectroscopy reveals that this source is a low-ionization nuclear emission-line region active galactic nucleus (AGN) and that there is a second candidate AGN on the opposite side of the cavity with a relative velocity of 370 km s ⁻¹ —if real, this implies the presence of a kiloparsec-separation dual AGN with a total binary mass of 6 ± 2 × 10 ¹⁰ M _⊙ , which would make this the most massive binary black hole system discovered to date. We propose that this unique stellar cavity is the result of a short-lived dynamical interaction between at least one supermassive black hole and the background stellar density field, caused either by three-body scattering during binary hardening or the induction of a dipole instability in the stellar density field.

We leverage JWST’s superb resolution to derive strong-lensing mass maps of 14 clusters, spanning a redshift range of z ∼ 0.25–1.06 and a mass range of M ₅₀₀ ∼ 2–12 × 10 ¹⁴ M _⊙ , from the Strong LensIng and Cluster Evolution (SLICE) JWST program. These clusters represent a small subsample of the first clusters observed in the SLICE program that are chosen based on the detection of new multiple-image constraints in the SLICE JWST NIRCam/F150W2 and F322W2 imaging. These constraints include new lensed dusty galaxies and new substructures in previously identified lensed background galaxies. Four clusters have never been modeled before. For the remaining 10 clusters, we present updated models based on JWST and Hubble Space Telescope imaging and, where available, ground-based spectroscopy. We model the global mass profile for each cluster and report the masses enclosed within 200 and 500 kpc. We report the number of new lensed source galaxies identified in the JWST imaging, which in one cluster is as high as 19 new lensed galaxies. The addition of new lensed source galaxies and constraints from substructure clumps improves the ability of strong-lensing models to accurately reproduce the interior mass distribution of each cluster. We also report the discovery of a candidate transient in a lensed image of the galaxy cluster SPT-CL J0516-5755. All lens models and their associated products are available for download at the Strong Lensing Cluster Atlas Data Base ( https://data.lam.fr/sl-cluster-atlas/ ), which is hosted at Laboratoire d’Astrophysique de Marseille.

Massive galaxy clusters act as prominent strong lenses. Due to a combination of observational biases, cluster evolution, and lensing efficiency, most of the known cluster lenses lie typically at z _l ∼ 0.2–0.7, with only a few prominent examples at higher redshifts. Here we report the first strong-lensing analysis of the massive galaxy cluster SPT-CL J0546-5345 at a redshift z _l = 1.07. This cluster was first detected through the Sunyaev–Zel’dovich effect, with a high estimated mass for its redshift of M _200,c = (7.95 ± 0.92) × 10¹⁴ M _⊙. Using recent JWST/NIRCam and archival Hubble Space Telescope imaging, we identify at least 10 secure and 6 candidate sets of multiply imaged background galaxies, which we use to constrain the mass distribution in the cluster. We derive effective Einstein radii of θ _E = 18 . ″ 1 ± 1 . ″ 8 for a source at z _s = 3 and θ _E = 27 . ″ 9 ± 2 . ″ 8 for a source at z _s = 9. The total projected mass within a 200 kpc radius around the strong-lensing region is M (14 M _⊙. While our results rely on photometric redshifts warranting spectroscopic follow-up, this central mass resembles that of the Hubble Frontier Fields clusters—although SPT-CL J0546-5345 is observed when the Universe was ∼3–4 Gyr younger. Amongst the multiply imaged sources, we identify a hyperbolic-umbilic-like configuration, and, thanks to its point-like morphology, a possible active galactic nucleus (AGN). If confirmed spectroscopically, it will add to just a handful of other quasars and AGN known to be multiply lensed by galaxy clusters.

The brightest cluster galaxies (BCGs) of today are passive and very massive galaxies at the center of their clusters. They still accrete mass by swallowing companions and flows of cold gas, processes which are regulated by radio-mode active galactic nucleus (AGN) feedback. However, the formation history of BCGs is still a matter of debate. We report new findings based on millimeter observations performed with the Northern Extended Millimeter Array (NOEMA) interferometer mapping the cold molecular gas (CO) that feeds the star formation of distant BCGs. We selected three sources among the strongest cool-core BCGs at intermediate redshifts (z ≃ 0.4), namely, RX 1532, MACS 1447, and CHIPS 1911. Previous unresolved millimeter observations and multi-wavelength analyses have shown that they are among the most star forming (SFR ≃ 100 M_⊙/yr) and gas rich (MH₂ ≃ 10¹¹ M_⊙) BCGs at intermediate redshifts. The selected sources are thus caught in a phase of rapid mass assembly, which makes them ideal targets for high-resolution observations of their molecular gas. We find that all three BCGs show point-like and steep-spectrum continuum emission at millimeter wavelengths, with a spectral slope of α = 0.6, which we interpret as being optically thin synchrotron emission from the AGN. By combining our NOEMA intensity and velocity maps with archival deep optical/infrared images from the Hubble Space Telescope, we unambiguously detected in situ star formation, filaments of accreting cold gas likely regulated by AGN feedback, a disturbed morphology associated with tidal tails of molecular gas, and gas compression and tails originating from the stripping of gas. While effective condensation of the intracluster medium is required to explain the large molecular gas reservoirs, the BCGs exhibit a broad variety of environment-driven mechanisms responsible for the processing of their cold gas: flows of cooling gas (RX 1532), ram pressure or sloshing of the intracluster medium (MACS 1447), and galactic tides (CHIPS 1911). This study thus provides new insights into the physical mechanisms responsible for the mass assembly of galaxies hosting AGN at the center of clusters.

The filamentary nebula encompassing the central galaxy of the Perseus Cluster, NGC 1275, is a complex structure extending dozens of kiloparsecs from NGC 1275. Decades of previous works have focused on establishing the primary formation and ionization mechanisms in different filaments. These studies have pointed to a lack of star formation in the majority of the filaments, the importance of magnetic fields and turbulence in several regions, and the role of interactions between the intracluster medium (ICM) and the cool gas in the filaments, as well as the role of interaction between the central radio source, 3C84, and the filaments. In this paper, we present multi-filter observations of the entire filamentary system that cover the optical bandpass, using the SITELLE instrument at the Canada-France-Hawai’i Telescope. Here, we use the data analysis software, LUCI (https://crhea93.github.io/LUCI/index.html), to produce flux maps of the prominent emission lines present in the filters: [O ii]λ3726/3729, [O iii]λ5007, Hβ, [N ii]λ6548, [N ii]λ6583, and Hα. We use these maps to produce Baldwin–Phillips–Terlevich and WHAN diagrams to study the ionization mechanisms at play in each distinct region of the filamentary nebula. First, we confirm the absence of [O iii]λ5007 in the extended filaments, although we detect this line in the central core, revealing a compact region where photoionization by the active galactic nucleus might affect local conditions. Our findings corroborate previous claims that the ionization in the extended filaments could be caused by the cooling ICM via collisional excitation and/or mixing. Moreover, they support the conclusion that magnetic fields play an important role in the formation and continued existence of the filaments.

We present Space Telescope Imaging Spectrograph observations from the Hubble Space Telescope of the supermassive black hole (SMBH) at the center of PKS 0745-191, a brightest cluster galaxy (BCG) undergoing powerful radio-mode active galactic nucleus (AGN) feedback (P _cav ~ 5 × 10⁴⁵ erg s⁻¹). These high-resolution data offer the first spatially resolved map of gas dynamics within an SMBH's sphere of influence under such powerful feedback. Our results reveal the presence of highly chaotic, nondrotational ionized gas flows on subkiloparsec scales, in contrast to the more coherent flows observed on larger scales. While radio-mode feedback effectively thermalizes hot gas in galaxy clusters on kiloparsec scales, within the core, the hot gas flow may decouple, leading to a reduction in angular momentum and supplying ionized gas through cooling, which could enhance accretion onto the SMBH. This process could, in turn, lead to a self-regulating feedback loop. Compared to other BCGs with weaker radio-mode feedback, where rotation is more stable, intense feedback may lead to more chaotic flows, indicating a stronger coupling between jet activity and gas dynamics. Additionally, we observe a sharp increase in velocity dispersion near the nucleus, consistent with a very massive M _BH ~ 1.5 × 10¹⁰ M _⊙ SMBH. The density profile of the ionized gas is also notably flat, paralleling the profiles observed in X-ray gas around galaxies where the Bondi radius is resolved. These results provide valuable insights into the complex mechanisms driving galaxy evolution, highlighting the intricate relationship between SMBH fueling and AGN feedback within the host galaxy.