In the era of large-scale surveys such as Euclid, machine learning has become an essential tool for identifying rare yet scientifically valuable objects, such as strong gravitational lenses. However, supervised machine-learning approaches require large quantities of labelled examples to train on, and the limited number of known strong lenses has led to a reliance on simulations for training. A well-known challenge is that machine-learning models trained on one data domain often underperform when applied to a different domain: in the context of lens finding, this means that strong performance on simulated lenses does not necessarily translate into equally good performance on real observations. In the Euclid Quick Data Release 1 (Q1), covering 63 deg2, 500 strong lens candidates were discovered through a synergy of machine learning, citizen science, and expert visual inspection. These discoveries now allow us to quantify this performance gap and investigate the impact of training on real data. We find that a network trained only on simulations recovers up to 92% of simulated lenses with 100% purity, but only achieves 50% completeness with 24% purity on real Euclid data. By augmenting training data with real Euclid lenses and non-lenses, completeness improves by 25–30% in terms of the expected yield of discoverable lenses in the Euclid Data Release 1 and the full Euclid Wide Survey. Roughly 20% of this improvement comes from the inclusion of real lenses in the training data, while 5–10% comes from exposure to a more diverse set of non-lenses and false positives from Q1. We show that the most effective lens-finding strategy for real-world performance combines the diversity of simulations with the fidelity of real lenses. This hybrid approach establishes a clear methodology for maximising lens discoveries in future data releases from Euclid and will likely also be applicable to other surveys such as the Vera Rubin Observatory’s Legacy Survey of Space and Time.

The Next Generation Virgo Cluster Survey (NGVS) is a deep, high resolution imaging campaign that used the 1 deg^2 MegaCam instrument on the Canada-France-Hawaii Telescope to carry out a comprehensive optical survey of the Virgo cluster, from its core to its virial radius. The NGVS covers a contiguous area of 104 deg^2 (8.63 Mpc^2 at the 16.5 Mpc distance of Virgo) in the u^*-,g-,i-, and z-band, with additional limited coverage in r. In this paper, we present the final catalog of Virgo galaxies across the entire NGVS area. The catalog includes 3680 galaxies considered to be bona fide members of the cluster, spanning a factor of 2.5 million in luminosity, from g = 8.42 mag to g = 24.41 mag (M_g = -22.67 mag to M_g = -6.68 mag). With 2100 previously uncataloged galaxies, the NGVS catalog augments the number of known Virgo members by a factor 2.3. The catalog is complete down to g = 18.6 mag (M_g=-12.5 mag, corresponding to a stellar mass M_* ∼ 1.6×10^7 M_⊙ for an old stellar population) and 50

We present the results of our pipeline for discovering strong gravitational lenses in the ongoing Ultraviolet Near-Infrared Optical Northern Survey (UNIONS). We successfully train a deep residual convolutional neural network based on CMU-Deeplens architecture, which is designed to detect strong lenses in ground-based imaging surveys. We train on images of real strong lenses and deploy on a sample of 8 million galaxies in areas with full coverage in the g , r , and i filters—the first multiband search for strong gravitational lenses in UNIONS. Following human inspection and grading, we report the discovery of a total of 1346 new strong-lens candidates, of which 146 are Grade A, 199 are Grade B, and 1001 are Grade C. Of these candidates, 283 have lens galaxy spectroscopic redshifts from the Sloan Digital Sky Survey, and an additional 297 have them from the Dark Energy Spectroscopic Instrument Data Release 1. We find 15 of these systems display evidence of both lens and source galaxy redshifts in spectral superposition. We also report the spectroscopic confirmation of seven lensed sources in high-quality systems, all with z > 2.1, using the Keck Near Infrared Echellette Spectrograph and the Gemini Near-Infrared Spectrograph.

We present COSMOS2025, the COSMOS-Web catalog of photometry, morphology, photometric redshifts, and physical parameters for more than 700 000 galaxies in the Cosmic Evolution Survey (COSMOS) field. This catalog is based on our James Webb Space Telescope 255 h COSMOS-Web program, which provides deep near-infrared imaging in four NIRCam (F115W, F150W, F277W, F444W) and one MIRI (F770W) filter over the central similar to 0.54 deg(2) (similar to 0.2 deg(2) for MIRI) in COSMOS. These data are combined with ground- and space-based data to derive photometric measurements of NIRCam-detected sources using both fixed-aperture photometry (on the space-based bands) and a profile-fitting technique on all 37 bands spanning 0.3 mu m to 8 mu m. We provide morphology for all sources from complementary techniques including profile fitting and machine-learning classification. We derive photometric redshifts, physical parameters, and non-parametric star formation histories from spectral energy distribution (SED) fitting. The catalog has been extensively validated against previous COSMOS catalogs and other surveys. Photometric redshift accuracy measured using spectroscopically confirmed galaxies out to z similar to 9 reaches sigma(MAD) = 0.012 at m(F444W) < 28 and remains at sigma(MAD) less than or similar to 0.03 as a function of magnitude, color, and galaxy type. This represents a factor of similar to 2 improvement at 26 AB mag compared to COSMOS2020. The catalog is approximately 80% complete at log(M-star/M-circle dot) similar to 9 at z similar to 10 and at log(M-star/M-circle dot) similar to 7 at z similar to 0.2, representing a gain of 1 dex compared to COSMOS2020. COSMOS2025 represents the definitive COSMOS-Web catalog. It is provided with complete documentation, together with redshift probability distributions, and it is ready for scientific exploitation today.

Under the standard model of hierarchical structure formation, the overall geometry of galaxy clusters is better described by a triaxial ellipse than by a sphere. As a result, the application of spherically symmetric models can result in significant biases, with masses derived from weak-lensing observations being particularly sensitive. These biases can be mitigated by fitting a triaxial model, but this requires deep multi-probe data along with a set of physically motivated models to describe them. We present a multi-probe triaxial analysis method based on the data available for galaxy clusters in the Cluster Heritage project with XMM-Newton - Mass Assembly and Thermodynamics at Endpoint of structure formation (CHEX-MATE), which includes X-ray data from XMM-Newton, Sunyaev-Zel'dovich effect maps from Planck and ACT, and weak-lensing data from Subaru. This work builds upon our previous development of a gas-only X-ray and Sunyaev-Zel'dovich triaxial fitting formalism in Paper I. After verifying our approach using mock observations of model clusters with known properties, we applied it to the CHEX-MATE galaxy cluster PSZ2 G313.33+61.13 (Abell 1689). We found that the cluster is elongated along the line of sight relative to the plane of sky by a factor of & Rscr;(LP) = 1.20 +/- 0.04. As a result, the weak-lensing mass obtained from our triaxial fit, M-200c = (13.88(-1.43)(+1.73)) & times; 10(14)M(circle dot ) , is significantly lower than the value of (17.77(-1.75)(+2.00))& times;10(14)M(circle dot )obtained from a spherically symmetric fit that otherwise employed the same method. Our triaxial fit finds a concentration ofc(200c)=8.66(-1.70)(+2.08), consistent with the spherically symmetric value of 9.99+2.26-1.78, which suggests that the unexpectedly high concentration in Abell 1689 is not due to triaxiality and orientation. We also measured the nonthermal pressure fraction at radii between 0.18-1.37 Mpc and found a minimum of approximately 20% at intermediate radii, increasing to near 30% at the smallest and largest radii, and with a typical measurement precision of +/- 5%.

Large imaging surveys in cosmology are detecting orders of magnitude more lens systems than known so far. This unprecedented dataset will lead to robust constraints on cosmology and galaxy evolution models. However, a preliminary careful characterization of the lens and source samples are mandatory. In this work, we report on a VLT/XShooter observation program of 67 lens systems to characterize their spectroscopic redshift distribution. These systems were previously detected on the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys by Huang et al. 2021 and Storfer et al. 2022 with deep residual neural network. We manage to measure redshifts for 58 lenses and 57 sources. We also identify 2 sources with indication of outflow in the shape of the emission lines and 7 sources with rotating disks in [OII] or Hα. We find no particular bias associated to the redshift measurement operation, meaning that our measured source redshift distribution is likely representative of the true one and can be used to calibrate analyses in large imaging surveys.

We present a weak-lensing shear analysis of 41 Planck SZ-selected galaxy clusters at 0.11≤ z≤ 0.55 from the CHEX-MATE sample, using wide-field Subaru/Suprime-Cam and CFHT/MegaPrime imaging from the AMALGAM project. We detect the azimuthally averaged weak-lensing signal around the X-ray peak of each cluster, achieving a median S/N of 6.5 per cluster. The 45^∘-rotated component has a median S/N of -0.1 and ranges from -1.8 to +1.8, consistent with zero. We model the excess surface mass density profile of each cluster with an NFW profile to infer weak-lensing mass and concentration constraints. The total systematic uncertainty in the weak-lensing mass calibration is assessed to be 8%. Using a hierarchical Bayesian framework, we then derive weak-lensing-calibrated scaling relations for the halo concentration, c_200, as a function of M_200 and redshift, and for the Planck SZ mass proxy, M_SZ, as a function of M_500 and redshift, while accounting for sample selection effects, weak-lensing modelling biases, and residual calibration uncertainty. At M_200=10^15M_⊙ and z=0.25, we find c_200=3.53±0.71 with an intrinsic scatter of 0.22±0.04 dex. The inferred normalisation and scatter are consistent with recent ΛCDM predictions for massive haloes, with no significant mass or redshift dependence over the probed range. For the Planck mass proxy, our baseline regression yields M_SZ/M_500=0.83±0.09 at M_500=7×10^14M_⊙ and z=0.25, with an intrinsic scatter of 0.10±0.02 dex. A restricted model with fixed unit mass slope and no redshift evolution gives 1-b=0.72±0.11. We also provide weak-lensing-calibrated posterior estimates of M_500 for the sample based on the baseline M_SZ–M_500–z relation. These results provide an initial weak-lensing mass calibration for CHEX-MATE multi-probe cluster studies.

The Cluster HEritage project with XMM-Newton - Mass Assembly and Thermodynamics at the Endpoint of structure formation (CHEX-MATE) is a programme to study a minimally biased sample of 118 galaxy clusters detected by Planck through the Sunyaev-Zeldovich effect. Accurate and precise mass measurements are required to exploit CHEX-MATE as an astrophysical laboratory and a calibration sample for cosmological probes in the era of large surveys. We measured masses based on the galaxy dynamics, which are highly complementary to weak-lensing or X-ray estimates. We analysed the sample with a uniform pipeline that is stable both for poorly sampled or rich clusters -using spectroscopic redshifts from public (NED, SDSS, and DESI) or private archives and dedicated observational programmes. We modelled the halo mass density and the anisotropy profile. Membership is confirmed with a cleaning procedure in phase space. We derived masses from measured velocity dispersions under the assumed model. We measured dynamical masses for 101 CHEX-MATE clusters with at least ten confirmed members within the virial radius r200c. Estimated redshifts and velocity dispersions agree with literature values when available. Validation with weak-lensing masses shows agreement within 8 +/- 16 (stat.) +/- 5 (sys.)%, and confirms dynamical masses as an unbiased proxy. Comparison with Planck masses shows them to be biased low by 34 +/- 3 (stat.) +/- 5 (sys.)%. A follow-up spectroscopic campaign is underway to cover the full CHEX-MATE sample.

The Euclid Early Release Observations (ERO) showcase Euclid's capabilities in advance of its main mission by targeting 17 astronomical objects, including galaxy clusters, nearby galaxies, globular clusters, and star-forming regions. A total of 24 hours of observing time was allocated in the early months of operation, and the scientific community was engaged through an early public data release. We describe the development of the ERO pipeline to create visually compelling images while simultaneously meeting the scientific demands within months of launch by leveraging a pragmatic data-driven development strategy. The pipeline's key requirements are to preserve the image quality and to provide flux calibration and photometry for compact and extended sources. The pipeline's five pillars are removal of instrumental signatures, astrometric calibration, photometric calibration, image stacking, and the production of science-ready catalogues for both the VIS and NISP instruments. We report a point spread function (PSF) with a full width at half maximum of 0.'' 16 in the optical I-E-band and 0.'' 49 in the near-infrared (NIR) bands Y-E, J(E), and H-E. Our VIS mean absolute flux calibration is accurate to about 1%, and the accuracy is 10% for NISP due to a limited calibration set; both instruments have considerable colour terms for individual sources. The median depth is 25.3 and 23.2 AB mag with a signal-to-noise ratio (S/N) of ten for galaxies, while it is 27.1 and 24.5 AB mag at an S/N of five for point sources for VIS and NISP, respectively. Euclid's ability to observe diffuse emission is exceptional due to its extended PSF nearly matching a pure diffraction halo, the best ever achieved by a wide-field high-resolution imaging telescope. Euclid offers unparalleled capabilities for exploring the low-surface brightness (LSB) Universe across all scales, providing high precision within a wide field of view (FoV), and opening a new observational window in the NIR. Median surface-brightness levels of 29.5 and 27.9, AB mag arcsec(-2) are achieved for VIS and NISP, respectively, for detecting a 10 '' x 10 '' extended feature at the 1 sigma level.

This paper presents a search for high redshift galaxies from the Euclid Early Release Observations program `Magnifying Lens.' The 1.5\,$ area covered by the twin Abell lensing cluster fields is comparable in size to the few other deep near-infrared surveys such as COSMOS, and so provides an opportunity to significantly increase known samples of rare UV-bright galaxies at $z UV Beyond their still uncertain role in reionisation, these UV-bright galaxies are ideal laboratories from which to study galaxy formation and constrain the bright-end of the UV luminosity function. Of the sources detected from a combined and NISP detection image, 168 do not have any appreciable VIS/ flux. These objects span a range in spectral colours, separated into two classes: 139 extremely red sources; and 29 Lyman-break galaxy candidates. Best-fit redshifts and spectral templates suggest the former is composed of both $z dusty star-forming galaxies and $z quiescent systems. The latter is composed of more homogeneous Lyman-break galaxies at $z In both cases, contamination by L- and T-type dwarfs cannot be ruled out with images alone. Additional contamination from instrumental persistence is investigated using a novel time series analysis. This work lays the foundation for future searches within the Euclid Deep Fields, where thousands more $z Lyman-break systems and extremely red sources will be identified.

The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a "collaboration of collaborations" that is using the Canada-France-Hawai'i Telescope, the Pan-STARRS telescopes, and the Subaru Observatory to obtain $ugriz$ images of a core survey region of 6250 deg$^2$ of the northern sky. The $10\sigma$ point source depth of the data, as measured within a 2-arcsecond diameter aperture, are $[u,g,r,i,z] = [23.7, 24.5, 24.2, 23.8, 23.3]$\ in AB magnitudes. UNIONS is addressing some of the most fundamental questions in astronomy, including the properties of dark matter, the growth of structure in the Universe from the very smallest galaxies to large-scale structure, and the assembly of the Milky Way. It is set to become the major ground-based legacy survey for the northern hemisphere for the next decade and provides an essential northern complement to the static-sky science of the Vera C. Rubin Observatory's Legacy Survey of Space and Time. UNIONS supports the core science mission of the {\it Euclid} space mission by providing the data necessary in the northern hemisphere for the calibration of the wavelength dependence of the {\it Euclid} point-spread function and derivation of photometric redshifts in the North Galactic Cap. This region contains the highest quality sky for {\it Euclid}, with low backgrounds from the zodiacal light, stellar density, extinction, and emission from Galactic cirrus. Here, we describe the UNIONS survey components, science goals, data products, and the current status of the overall program.

We present the first analysis of the Early Release Observations (ERO) program that targets fields around two lensing clusters, Abell 2390 and Abell 2764. We use imaging data from the Visible instrument (VIS) and the Near-Infrared Spectrometer and Photometer (NISP) to produce photometric catalogs for a total of $ 500\,000$ objects. The imaging data reach a typical depth of $5\ in the range 25.1--25.4 AB in the NISP bands and 27.1--27.3 AB in the VIS band. Using the Lyman-break method in combination with photometric redshifts, we searched for high-redshift galaxies. We identified $30$ Lyman-break galaxy (LBG) candidates at $z>6$ and 139 extremely red sources (ERSs), most of which likely lie at lower redshift. The VIS imaging is deeper than the NISP imaging, which means that we can routinely identify high-redshift Lyman-break galaxies at about a magnitude of 3, which reduces contamination by brown dwarf stars and low-redshift galaxies. The difficulty of spatially resolving most of these sources in 0 $ imaging means that it is difficult to distinguish between galaxies and quasars. Spectroscopic follow-up campaigns of these bright sources will help us to constrain the bright end of the ultraviolet galaxy luminosity function and the quasar luminosity function at $z>6$, and it will constrain the physical nature of these objects. Additionally, we performed a combined strong- and weak-lensing analysis of A2390, and we show that will contribute to constraining the virial mass of galaxy clusters better. We also identify optical and near-infrared counterparts of known $z>0.6$ clusters in these data. These counterparts exhibit strong-lensing features. This establishes that can characterize high-redshift clusters. Finally, we provide a glimpse of the ability of to map the intracluster light out to larger radii than current facilities, which enables us to understand the cluster assembly history better and to map the dark matter distribution. This initial dataset illustrates the diverse spectrum of legacy science that is possible with the survey.

We report the spectroscopic confirmation of the background source of the most distant Einstein ring known to date, the COSMOS-Web ring. This system consists of a complete Einstein ring at z = 5.1, which is lensed by a massive early-type galaxy at z similar to 2. The redshift z = 5.1043 +/- 0.0004 is unambiguously identified with our NOEMA and Keck/MOSFIRE spectroscopy; the NOEMA observations reveal the CO(4-3) and CO(5-4) lines at > 8 sigma, and the MOSFIRE data detect [O II] at similar to 6 sigma. Using multiwavelength photometry spanning near-infrared to radio bands, we find that the lensed galaxy is a dust-obscured starburst (M-star similar to 1.8 x 10(10) M-circle dot, SFRIR similar to 60 M-circle dot yr(-1)) with a high star formation efficiency (gas depletion time tau(dep) < 100 Myr), as indicated by the [C I](1-0) non-detection. The redshift confirmation re-validates that the total lens mass budget within the Einstein radius is fully accounted for by the stellar and dark matter components, without the need of modifying the initial mass function or dark matter distribution profile. This work paves the way for detailed studies and future follow-ups of this unique lensing system, which is an ideal laboratory for studying mass distribution at z similar to 2 and physical conditions of star formation at z similar to 5.

We analysed the kinematical properties of the CHEX-MATE galaxy cluster sample. Our study is based on the radial velocities retrieved from the SDSS DR18, DESI, and NED spectroscopic databases and new data obtained with the 10.4 m GTC and ESO-NTT telescopes. We derived cluster mass profiles for 75 clusters using the MG-MAMPOSST procedure, which recovers the gravitational potential and the anisotropy profiles from line-of-sight velocities and projected positions of galaxy members. The standard Navarro-Frenk-White (NFW) model and the Burkert model, with flatter cores than the NFW, both adequately fit the kinematic data, with only a marginal statistical preference for one model over the other. An estimation of the mass bias (1-B1) = M500SZ/M500M ( 1 - B 1 ) = M 500 SZ / M 500 M $ (1-B_1) = M<<^>>{\mathrm{SZ}}_{500}/M<<^>>{M}_{500} $ was performed via a comparison with Sunyaev-Zel'dovich-X-ray-calibrated mass estimates, resulting in a value of 0.54 +/- 0.11 when four evidently disturbed clusters are removed from the sample. We assessed the dynamical state of the clusters by inferring the Anderson-Darling coefficient (A2) and the fraction of galaxies in substructures (fsub). Except for a few cases, we find relatively low values for A2, which suggests that CHEX-MATE clusters are not too far from relaxation. Moreover, no significant trends emerge between A2 and fsub, nor between the log-masses estimated by MG-MAMPOSST and those based on the Sunyaev-Zel'dovich effect calibrated through X-rays measurements. We studied the concentration-mass relation for the sample; despite the large scatter, we observe signs of an increasing trend for high-mass clusters, in agreement with recent theoretical expectations. Finally, our analysis of the radial anisotropy profiles of member galaxies - stacked in five bins of mass and redshift - reveals that orbits tend to be isotropic at the centre and more radial towards the edge, as found in previous studies. A slight trend of increasing radial orbits at r200 is observed in clusters with larger velocity dispersions.

The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.

The Euclid Wide Survey (EWS) is predicted to find approximately 170 000 galaxy-galaxy strong lenses from its lifetime observation of 14 000 deg(2) of the sky. Detecting this many lenses by visual inspection with professional astronomers and citizen scientists alone is infeasible. As a result, machine learning algorithms, particularly convolutional neural networks (CNNs), have been used as an automated method of detecting strong lenses, and have proven fruitful in finding galaxy-galaxy strong lens candidates, such that the usage of CNNs in lens identification has increased. We identify the major challenge to be the automatic detection of galaxy-galaxy strong lenses while simultaneously maintaining a low false positive rate, thus producing a pure and complete sample of strong lens candidates from Euclid with a limited need for visual inspection. One aim of this research is to have a quantified starting point on the achieved purity and completeness with our current version of CNN-based detection pipelines for the VIS images of EWS. This work is vital in preparing our CNN-based detection pipelines to be able to produce a pure sample of the >100 000 strong gravitational lensing systems widely predicted for Euclid. We select all sources with VIS I-E < 23 mag from the Euclid Early Release Observation imaging of the Perseus field. We apply a range of CNN architectures to detect strong lenses in these cutouts. All our networks perform extremely well on simulated data sets and their respective validation sets. However, when applied to real Euclid imaging, the highest lens purity is just similar to 11%. Among all our networks, the false positives are typically identifiable by human volunteers as, for example, spiral galaxies, multiple sources, and artifacts, implying that improvements are still possible, perhaps via a second, more interpretable lens selection filtering stage. There is currently no alternative to human classification of CNN-selected lens candidates. Given the expected similar to 10(5) lensing systems in Euclid, this implies 10(6) objects for human classification, which while very large is not in principle intractable and not without precedent.

Aims. We provide an in-depth analysis of the COSMOS-Web ring, an Einstein ring at z=2 that we serendipitously discovered in the COSMOS-Web survey and possibly the most distant lens discovered to date. Methods. We extract the visible and NIR photometry from more than 25 bands and we derive the photometric redshifts and physical properties of both the lens and the source with three different SED fitting codes. Using JWST/NIRCam images, we also produce two lens models to (i) recover the total mass of the lens, (ii) derive the magnification of the system, (iii) reconstruct the morphology of the lensed source, and (iv) measure the slope of the total mass density profile of the lens. Results. The lens is a very massive and quiescent (sSFR < 10^(-13) yr-1) elliptical galaxy at z = 2.02 \pm 0.02 with a total mass Mtot(<thetaE) = (3.66 \pm 0.36) x 10^11 Msun and a stellar mass M* = (1.37 \pm 0.14) x 10^11 Msun. Compared to SHMRs from the literature, we find that the total mass is consistent with the presence of a DM halo of mass Mh = 1.09^(+1.46)_(-0.57) x 10^13 Msun. In addition, the background source is a M* = (1.26 \pm 0.17) x 10^10 Msun star-forming galaxy (SFR=(78 \pm 15) Msun/yr) at z = 5.48 \pm 0.06. Its reconstructed morphology shows two components with different colors. Dust attenuation values from SED fitting and nearby detections in the FIR also suggest it could be partially dust-obscured. Conclusions. We find the lens at z=2. Its total, stellar, and DM halo masses are consistent within the Einstein ring, so we do not need any unexpected changes in our description of the lens (e.g. change its IMF or include a non-negligible gas contribution). The most likely solution for the lensed source is at z = 5.5. Its reconstructed morphology is complex and highly wavelength dependent, possibly because it is a merger or a main sequence galaxy with a heterogeneous dust distribution.

The 3D geometries of high-redshift galaxies remain poorly understood. We build a differentiable Bayesian model and use Hamiltonian Monte Carlo to efficiently and robustly infer the 3D shapes of star-forming galaxies in James Webb Space Telescope Cosmic Evolution Early Release Science observations with log M * / M ⊙ = 9.0 – 10.5 at z = 0.5–8.0. We reproduce previous results from the Hubble Space Telescope Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey in a fraction of the computing time and constrain the mean ellipticity, triaxiality, size, and covariances with samples as small as ∼50 galaxies. We find high 3D ellipticities for all mass–redshift bins, suggesting oblate (disky) or prolate (elongated) geometries. We break that degeneracy by constraining the mean triaxiality to be ∼1 for log M * / M ⊙ = 9.0 – 9.5 dwarfs at z > 1 (favoring the prolate scenario), with significantly lower triaxialities for higher masses and lower redshifts indicating the emergence of disks. The prolate population traces out a “banana” in the projected b / a – log a diagram with an excess of low- b / a , large- log a galaxies. The dwarf prolate fraction rises from ∼25% at z = 0.5–1.0 to ∼50%–80% at z = 3–8. Our results imply a second kind of disk settling from oval (triaxial) to more circular (axisymmetric) shapes with time. We simultaneously constrain the 3D size–mass relation and its dependence on 3D geometry. High-probability prolate and oblate candidates show remarkably similar Sérsic indices ( n ∼ 1), nonparametric morphological properties, and specific star formation rates. Both tend to be visually classified as disks or irregular, but edge-on oblate candidates show more dust attenuation. We discuss selection effects, follow-up prospects, and theoretical implications.

We characterise the entropy profiles of 32 very high mass (M_500>7.75×10^14 M_⊙) galaxy clusters (HIGHMz), selected from the CHEX-MATE sample, to study the intracluster medium (ICM) entropy distribution in a regime where non-gravitational effects are minimised. Using XMM-Newton measurements, we measure the entropy profiles up to R_500 for all objects. The scaled profiles exhibit large dispersion in the central regions, but converge rapidly to the expectation from pure gravitational collapse beyond the core. We quantify the correlation between the ICM morphological parameters and scaled entropy as a function of radius, showing that morphologically relaxed (disturbed) objects have low (high) central entropy. We compare our data to other observational samples, finding differences in normalisation which are linked to the average mass of the samples in question. We find that a weaker mass dependence than self-similar in the scaling (Am -0.25) allows us to minimise the dispersion in the radial range [0.3-0.8]R_500 for clusters spanning over a decade in mass. The deviation from self-similarity is radially dependent and is more pronounced at small and intermediate radii than at R_500. We also investigate the distribution of central entropy K_0, finding no evidence for bimodality, and outer slopes α, which peaks at 1.1. Using weak lensing masses, we find indication for a small suppression of the scatter ( 30 using masses derived from Yx in the rescaling. Finally, we compare to recent cosmological numerical simulations from THE THREE HUNDRED and MACSIS, finding good agreement with our observational data. These results provide a robust observational benchmark in the gravity-dominated regime and will serve as a future reference for samples at lower mass, higher redshifts, and for ongoing work using cosmological numerical simulations.

This paper presents a search for high redshift galaxies from the Euclid Early Release Observations program "Magnifying Lens." The 1.5 deg$^2$ area covered by the twin Abell lensing cluster fields is comparable in size to the few other deep near-infrared surveys such as COSMOS, and so provides an opportunity to significantly increase known samples of rare UV-bright galaxies at $z\approx6-8$ ($M_{\rm UV}\lesssim-22$). Beyond their still uncertain role in reionisation, these UV-bright galaxies are ideal laboratories from which to study galaxy formation and constrain the bright-end of the UV luminosity function. Of the 501994 sources detected from a combined $Y_{\rm E}$, $J_{\rm E}$, and $H_{\rm E}$ NISP detection image, 168 do not have any appreciable VIS/$I_{\rm E}$ flux. These objects span a range in spectral colours, separated into two classes: 139 extremely red sources; and 29 Lyman-break galaxy candidates. Best-fit redshifts and spectral templates suggest the former is composed of both $z\gtrsim5$ dusty star-forming galaxies and $z\approx1-3$ quiescent systems. The latter is composed of more homogeneous Lyman break galaxies at $z\approx6-8$. In both cases, contamination by L- and T-type dwarfs cannot be ruled out with Euclid images alone. Additional contamination from instrumental persistence is investigated using a novel time series analysis. This work lays the foundation for future searches within the Euclid Deep Fields, where thousands more $z\gtrsim6$ Lyman break systems and extremely red sources will be identified.