Research Articles (Physics)

Permanent URI for this collectionhttps://hdl.handle.net/10566/726

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Euclid preparation: LXV. determining the weak lensing mass accuracy and precision for galaxy clusters
(EDP Sciences, 2025) Karagiannis, Dionysios; Ingoglia, Lorenzo; Sereno, Mauro
The ability to measure unbiased weak-lensing (WL) masses is a key ingredient to exploit galaxy clusters as a competitive cosmological probe with the ESA Euclid survey or future missions. We investigate the level of accuracy and precision of cluster masses measured with the Euclid data processing pipeline. We use the DEMNUni-Cov N-body simulations to assess how well the WL mass probes the true halo mass, and, then, how well WL masses can be recovered in the presence of measurement uncertainties. We consider different halo mass density models, priors, and mass point estimates, that is the biweight, mean, and median of the marginalised posterior distribution and the maximum likelihood parameter. WL mass differs from true mass due to, for example, the intrinsic ellipticity of sources, correlated or uncorrelated matter and large-scale structure, halo triaxiality and orientation, and merging or irregular morphology. In an ideal scenario without observational or measurement errors, the maximum likelihood estimator is the most accurate, with WL masses biased low by {bM} =a-14.6-±-1.7% on average over the full range M200c > 5×1013 M⊙ and z < 1. Due to the stabilising effect of the prior, the biweight, mean, and median estimates are more precise, that is with smaller intrinsic scatter. The scatter decreases with increasing mass and informative priors can significantly reduce the scatter. Halo mass density profiles with a truncation provide better fits to the lensing signal, while the accuracy and precision are not significantly affected. We further investigate the impact of various additional sources of systematic uncertainty on the WL mass estimates, namely the impact of photometric redshift uncertainties and source selection, the expected performance of Euclid cluster detection algorithms, and the presence of masks. Taken in isolation, we find that the largest effect is induced by non-conservative source selection with {bM} =a-33.4-±-1.6%. This effect can be mostly removed with a robust selection. As a final Euclid-like test, we combine systematic effects in a realistic observational setting and find {bM} =a-15.5-±-2.4% under a robust selection. This is very similar to the ideal case, though with a slightly larger scatter mostly due to cluster redshift uncertainty and miscentering.
Tracing AGN–galaxy co-evolution with UV line-selected obscured AGN
(Oxford University Press, 2025) Jarvis, Matthew; Whittam, Imogen; Barchiesi, Luigi
Understanding black hole–galaxy co-evolution and the role of active galactic nucleus (AGN) feedback requires complete AGN samples, including heavily obscured systems. Such sources are key to constraining the black hole accretion rate density over cosmic time, yet they are challenging to identify and characterize across most wavelengths. In this work, we present the first ultraviolet (UV) line-selected ([Nev]3426 Å and Civ 1549 Å) sample of obscured AGN with full X-ray-to-radio coverage, assembled by combining data from the Chandra COSMOS Legacy survey, the COSMOS2020 UV–NIR catalogue, mid- and far-IR photometry from XID+, and radio observations from the Very Large Array and MeerKAT International GHz Tiered Extragalactic Exploration Survey (MIGHTEE) surveys. Using cigale to perform spectral energy distribution (SED) fitting, we analyse 184 obscured AGNs at 0.6 < z < 1.2 and 1.5 < z < 3.1, enabling detailed measurements of AGN and host-galaxy properties, and direct comparison with simba hydrodynamical simulations. We find that X-ray and radio data are essential for accurate SED fits, with the radio band proving critical when X-ray detections are missing or in cases of poor IR coverage. Comparisons with matched non-active galaxies and simulations suggest that the [Nev]-selected sources are in a pre-quenching stage, while the Civ-selected ones are likely quenched by AGN activity. Our results indicate that [Nev] and Civ selections target galaxies in a transient phase of their co-evolution, characterized by intense, obscured accretion, and pave the way for future extensions with upcoming large area high-z spectroscopic surveys.
The total rest-frame UV luminosity function from 3 < z < 5: a simultaneous study of AGN and galaxies from −28 < MUV < −16
(Oxford University Press, 2023) Jarvis, Matthew; Adams, Nathan; Bowler, Rebecca
We present measurements of the rest-frame ultraviolet luminosity function (LF) at redshifts z = 3, z = 4, and z = 5, using 96894, 38655, and 7571 sources, respectively, to map the transition between active galactic nuclei (AGN) and galaxy-dominated ultraviolet emission shortly after the epoch of reionization (EoR). Sources are selected using a comprehensive photometric redshift approach, using 10 deg2 of deep extragalactic legacy fields covered by both HSC and VISTA. The use of template fitting spanning a wavelength range of 0.3–2.4 μm achieves 80–90 per cent completeness, much higher than the classical colour–colour cut methodology. The measured LF encompasses −26 < MUV < −19.25. This is further extended to −28.5 < MUV < −16 using complementary results from other studies, allowing for the simultaneous fitting of the combined AGN and galaxy LF. We find that there are fewer UV luminous galaxies (MUV < −22) at z ∼ 3 than z ∼ 4, indicative of an onset of widespread quenching alongside dust obscuration, and that the evolution of the AGN LF is very rapid, with their number density rising by around two orders of magnitude from 3 < z < 6. It remains difficult to determine if a double power law functional form is preferred over the Schechter function to describe the galaxy UV LF. Estimating the hydrogen ionizing photon budget from our UV LFs, we find that AGN can contribute to, but cannot solely maintain, the reionization of the Universe at z = 3–5. However, the rapidly evolving AGN LF strongly disfavours a significant contribution within the EoR.
Group therapy for Halos: advancing halo mass estimation for Galaxy groups
(Cambridge University Press, 2026) Cluver, Michelle E.; Van Kempen, Wesley; Taylor, Edward N.
Accurate estimation of dark matter halo masses for galaxy groups is central to studies of galaxy evolution and for leveraging group catalogues as cosmological probes. In this work, we present a comprehensive evaluation and calibration of two complementary halo mass estimators: a dynamical estimator based on a modified virial theorem (MVT), and an empirical summed stellar mass to halo mass relation (sSHMR) which uses the summed mass of the three most massive group galaxies as a proxy for halo mass. Using a suite of state-of-the-art semi-analytic models (SAMs; Shark, SAGE, and GAEA) to produce observationally motivated mock light-cone catalogues, we rigorously quantify the accuracy, uncertainty, and model dependence of each method. The MVT halo mass estimator achieves negligible systematic bias (mean Δ = −0.01 dex) and low scatter (mean σ = 0.20 dex) as a function of the predicted halo mass, with no sensitivity to the SAM baryonic physics. The calibrated sSHMR yields the highest precision, with mean Δ = 0.02 dex and mean σ = 0.14 dex as a function of the predicted halo mass but exhibits greater model dependence due to its sensitivity to varying baryonic physics and physical prescriptions across the SAMs. We demonstrate the application of these estimators to observational group catalogues, including the construction of the empirical halo mass function and the mapping of quenched fractions in the stellar mass–halo mass plane. We provide clear guidance on the optimal application of each method: the MVT is recommended for GAMA-like surveys (i < 19.2) calibrated to z < 0.1 and should be used for studies that require minimal model dependence, while the sSHMR is optimal for high-precision halo mass estimation across diverse catalogues with magnitude limits of Z < 21.2 or brighter and to redshifts of z ≤ 0.3. These calibrated estimators will be of particular value for upcoming wide-area spectroscopic surveys, enabling robust and precise analyses between the galaxy–halo connection and the underlying dark matter distribution.
Receiver design for the REACH global 21-cm signal experiment
(Springer Science and Business Media B.V., 2025) Spinelli Marta; Roque, Ian; Razavi-Ghods, Nima
We detail the REACH radiometric system designed to enable measurements of the 21-cm neutral hydrogen line. Included is the radiometer architecture and end-to-end system simulations as well as a discussion of the challenges intrinsic to highly-calibratable system development. Following this, we share laboratory results based on the calculation of noise wave parameters utilising an over-constrained least squares approach. For five hours of integration on a custom-made source with comparable impedance to that of the antenna used in the field, we demonstrate a calibration RMSE of 80 mK. This paper therefore documents the state of the calibrator and data analysis in December 2022 in Cambridge before shipping to South Africa.
MIGHTEE: exploring the relationship between spectral index, redshift, and radio luminosity
(Oxford University Press, 2025) Jarvis, Matt J.; Vaccari, Mattia; Whittam, Imogen H
It has been known for many years that there is an apparent trend for the spectral index (α) of radio sources to steepen with redshift z, which has led to attempts to select high-redshift objects by searching for radio sources with steep spectra. In this study, we use data from the MeerKAT, Low Frequency Array survey, Giant Metre-wave Radio Telescope survey (GMRT), and uGMRT telescopes, particularly using the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) and superMIGHTEE surveys, to select compact sources over a wide range of redshifts and luminosities. We investigate the relationship between spectral index, luminosity and redshift and compare our results to those of previous studies. Although there is a correlation between α and z in our sample for some combinations of frequency where good data are available, there is a clear offset between the α–z relations in our sample and those derived previously from samples of more luminous objects; in other words, the α–z relation is different for low and high-luminosity sources. The relationships between α and luminosity are also weak in our sample but in general the most luminous sources are steeper-spectrum and this trend is extended by samples from previous studies. In detail, we argue that both a α–luminosity relation and an α–z relation can be found in the data, but it is the former that drives the apparent α–z relation observed in earlier work, which only appears because of the strong redshift–luminosity relation in bright, flux density-limited samples. Steep-spectrum selection should be applied with caution in searching for high-z sources in future deep surveys.
Euclid I. overview of the euclid mission
(EDP Sciences, 2025) Karagiannis, Dionysios; Mellier, Yannick; Abdurro’uf,
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 deg2 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.
Astronomaly Protege: discovery through human-machine collaboration
(American Astronomical Society, 2025) Lochner, Michelle; Rudnick, Lawrence
Modern telescopes generate catalogs of millions of objects with the potential for new scientific discoveries, but this is beyond what can be examined visually. Here we introduce ASTRONOMALY: PROTEGE, an extension of the general-purpose machine-learning-based active anomaly detection framework ASTRONOMALY. PROTEGE is designed to provide well-selected recommendations for visual inspection, based on a small amount of optimized human labeling. The resulting sample contains rare or unusual sources that are simultaneously as diverse as the human trainer chooses and of scientific interest to them. We train PROTEGE on images from the MeerKAT Galaxy Cluster Legacy Survey, leveraging the self-supervised deep learning algorithm Bootstrap Your Own Latent to find a low-dimensional representation of the radio galaxy cutouts. By operating in this feature space, PROTEGE is able to recommend interesting sources with completely different morphologies in image space to those it has been trained on. This provides important advantages over similarity searches, which can only find more examples of known sources, or blind anomaly detection, which selects unusual but not necessarily scientifically interesting sources. Using an evaluation subset, we show that, with minimal training, PROTEGE provides excellent recommendations and find that it is even able to recommend sources that the authors missed. We briefly highlight some of PROTEGE's top recommendations, which include X- and circular-shaped sources, filamentary structures, and one-sided structures. These results illustrate the power of an optimized human-machine collaboration, such as PROTEGE, to make unexpected discoveries in samples beyond human-accessible scales
Tracing the evolutionary pathways of dust and cold gas in high-z quiescent galaxies with SIMBA
(EDP Sciences, 2025) Davé, Romeel; Lorenzon, Giuliano; Donevski, Darko
Recent discoveries of copious amounts of dust in quiescent galaxies (QGs) at high redshifts (z ³ 1 2) challenge the conventional view that these objects have a negligible interstellar medium (ISM) in proportion to their stellar mass. We made use of the SIMBA hydrodynamic cosmological simulation to explore how dust and cold gas evolve in QGs and are linked to the quenching processes affecting them. We applied a novel method for tracking the changes in the ISM dust abundance across the evolutionary history of QGs identified at 0 < z ² 2 in both cluster and field environments. The QGs transition from a diversity of quenching pathways, both rapidly and slowly, and they exhibit a wide range of times that elapsed between the quenching event and cold gas removal (from -650 Myr to -8 Gyr). Contrary to some claims, we find that quenching modes attributed to the feedback from active galactic nuclei (AGNs) do not affect dust and cold gas within the same timescales. Remarkably, QGs may replenish their dust content in the quenched phase primarily due to internal processes and marginally by external factors such as minor mergers. Prolonged grain growth on gas-phase metals appears to be the key mechanism for dust re-formation, which is effective within -100 Myr after the quenching event and rapidly increases the dust-to-gas mass ratio in QGs above the standard values (δDGR ³ 1/100). Consequently, despite heavily depleted cold gas reservoirs, roughly half of QGs maintain little evolution of their ISM dust with stellar age within the first 2 Gyr following the quenching. Overall, we predict that relatively dusty QGs (Mdust/M ³ 103 104) arise from both fast and slow quenchers, and they are prevalent in quenched systems of intermediate and low stellar masses (9 < log(M/M) < 10.5). This strong prediction poses an immediate quest for observational synergy between, for example, the James Webb Space Telescope (JWST) and the Atacama Large Millimetre Array (ALMA).
Low-frequency turnover star-forming galaxies I: Radio continuum observations and global properties
(Cambridge University Press, 2025) Cluver, Michelle; Grundy, Joe Arthur; Seymour, Nicholas
There is growing evidence that the broadband radio spectral energy distributions (SEDs) of star-forming galaxies (SFGs) contain a wealth of complex physics. In this paper we aim to determine the physical emission and loss processes causing radio SED curvature and steepening to see what observed global astrophysical properties, if any, are correlated with radio SED complexity. To do this, we have acquired radio continuum data between 70 MHz and 17 GHz for a sample of 19 southern local (z < 0.04) SFGs. Of this sample 11 are selected to contain low-frequency (<300 MHz) turnovers (LFTOs) in their SEDs and eight are control galaxies with similar global properties. We model the radio SEDs for our sample using a Bayesian framework whereby radio emission (synchrotron and free-free) and absorption or loss processes are included modularly. We find that without the inclusion of higher frequency data (>17 GHz) single synchrotron power-law based models are always preferred for our sample; however, additional processes including free-free absorption (FFA) and synchrotron losses are often required to accurately model radio SED complexity in SFGs. The fitted synchrotron spectral indices range from −0.45 to −1.07 and are strongly anticorrelated with stellar mass suggesting that synchrotron losses are the dominant mechanism acting to steepen the spectral index in larger/more massive nearby SFGs. We find that LFTOs in the radio SED are independent from the inclination of SFGs; however, higher inclination galaxies tend to have steeper fitted spectral indices indicating losses to diffusion of cosmic ray electrons into the galactic halo. Four of five of the merging systems in our SFG sample have elevated specific star formation rates and flatter fitted spectral indices with unconstrained LFTOs. Lastly, we find no significant separation in global properties between SFGs with or without modelled LFTOs. Overall these results suggest that LFTOs are likely caused by a combination of FFA and ionisation losses in individual recent starburst regions with specific orientations and interstellar medium properties that, when averaged over the entire galaxy, do not correlate with global astrophysical properties.
Euclid preparation: LVIII. Detecting extragalactic globular clusters in the Euclid survey
(EDP Sciences, 2025) Karagiannis, Dionysios; Voggel, Karina; Lançon, Ariane
Extragalactic globular clusters (EGCs) are an abundant and powerful tracer of galaxy dynamics and formation, and their own formation and evolution is also a matter of extensive debate. The compact nature of globular clusters means that they are hard to spatially resolve and thus study outside the Local Group. In this work we have examined how well EGCs will be detectable in images from the Euclid telescope, using both simulated pre-launch images and the first early-release observations of the Fornax galaxy cluster. The Euclid Wide Survey will provide high-spatial resolution VIS imaging in the broad IE band as well as near-infrared photometry (YE, JE, and HE). We estimate that the 24 719 known galaxies within 100 Mpc in the footprint of the Euclid survey host around 830 000 EGCs of which about 350 000 are within the survey's detection limits. For about half of these EGCs, three infrared colours will be available as well. For any galaxy within 50 Mpc the brighter half of its GC luminosity function will be detectable by the Euclid Wide Survey. The detectability of EGCs is mainly driven by the residual surface brightness of their host galaxy. We find that an automated machine-learning EGC-classification method based on real Euclid data of the Fornax galaxy cluster provides an efficient method to generate high purity and high completeness GC candidate catalogues. We confirm that EGCs are spatially resolved compared to pure point sources in VIS images of Fornax. Our analysis of both simulated and first on-sky data show that Euclid will increase the number of GCs accessible with high-resolution imaging substantially compared to previous surveys, and will permit the study of GCs in the outskirts of their hosts. Euclid is unique in enabling systematic studies of EGCs in a spatially unbiased and homogeneous manner and is primed to improve our understanding of many understudied aspects of GC astrophysics
Strong nebular He II emission induced by He+ ionizing photons escaping through the clumpy winds of massive stars
(EDP Sciences, 2025) Paul, Sourabh; Roy, Arpita; Krumholz, Mark
Context. The origin of nebular HeII emission in both local and high-redshift galaxies remains an unsolved problem. Various theories have been proposed to explain it, including HeII-ionizing photons produced by high mass X-ray binaries, ultra-luminous X-ray sources, or - stripped He stars produced by binary interaction or evolution of rapidly rotating (v/vcrit-a 0.4) single massive stars, shock ionization, and hidden active galactic nuclei. All of these theories have shortcomings, however, leaving the cause of nebular HeII emission unclear. Aims. We investigate the hypothesis that the photons responsible for driving nebular HeII emission are produced by the evolution of single massive stars and/or Wolf-Rayet (WR) stars whose winds are on the verge of becoming optically thin due to clumping, thus allowing significant escape of hard ionizing photons. We combined models of stellar evolution with population synthesis and nebular models to identify the most favorable scenarios for producing nebular HeII via this channel. Methods. We used the Modules for Experiments in Stellar Astrophysics (MESA) code to compute evolutionary tracks for stars with initial masses of 10-150-M- and a range of initial metallicities and rotation rates. We then combined these tracks with a range of custom treatments of stellar atmospheres, which were intended to capture the effects of clumping, in the population synthesis code Stochastically Lighting Up Galaxies (SLUG) in order to produce the total ionizing photon budgets and spectra. We used these spectra as inputs to CLOUDY calculations of nebular emission at a range of nebular densities and metallicities. Results. We find that if WR winds are clumpy enough to become close to optically thin, stellar populations with a wide range of metallicities and rotation rates can produce HeII ionizing photons at rates sufficient to explain the observed nebular I(HeII)/I(Hβ) ratio a0.004-0.07 found in HeII-emitting galaxies. Metal-poor rapidly rotating stellar populations ([Fe/H]=-2.0, v/vcrit-=-0.4) also reach these levels of HeII production, even for partially clumpy winds. These scenarios also yield HeII, Hβ, and - blue bumpa line equivalent widths comparable to those observed in HeII emitters. Only for homogeneous non-clumpy winds did we fail to find combinations of metallicity and stellar rotation rate that yield I(HeII)/I(Hβ) values as high as those observed in HeII emitters. Conclusions. Contrary to previous findings, we conclude that single WR stars can be a strong source for nebular HeII emission if their winds are sufficiently clumpy. This scenario also reproduces a range of other properties found in HeII emitters, suggesting that hard photons escaping through clumpy WR winds are a strong candidate to explain nebular HeII-emission.
Euclid preparation: LXVII. Deep learning true galaxy morphologies for weak lensing shear bias calibration
(EDP Sciences, 2025) Karagiannis Dionysis; Csizi, Benjamin; Schrabback, Tim
To date, galaxy image simulations for weak lensing surveys usually approximate the light profiles of all galaxies as a single or double Sérsic profile, neglecting the influence of galaxy substructures and morphologies deviating from such a simplified parametric characterisation. While this approximation may be sufficient for previous data sets, the stringent cosmic shear calibration requirements and the high quality of the data in the upcoming Euclid survey demand a consideration of the effects that realistic galaxy substructures and irregular shapes have on shear measurement biases. Here we present a novel deep learning-based method to create such simulated galaxies directly from Hubble Space Telescope (HST) data. We first build and validate a convolutional neural network based on the wavelet scattering transform to learn noise-free representations independent of the point-spread function (PSF) of HST galaxy images. These can be injected into simulations of images from Euclid's optical instrument VIS without introducing noise correlations during PSF convolution or shearing. Then, we demonstrate the generation of new galaxy images by sampling from the model randomly as well as conditionally. In the latter case, we fine-tune the interpolation between latent space vectors of sample galaxies to directly obtain new realistic objects following a specific Sérsic index and half-light radius distribution. Furthermore, we show that the distribution of galaxy structural and morphological parameters of our generative model matches the distribution of the input HST training data, proving the capability of the model to produce realistic shapes. Next, we quantify the cosmic shear bias from complex galaxy shapes in Euclid-like simulations by comparing the shear measurement biases between a sample of model objects and their best-fit double-Sérsic counterparts, thereby creating two separate branches that only differ in the complexity of their shapes. Using the Kaiser, Squires, and Broadhurst shape measurement algorithm, we find a multiplicative bias difference between these branches with realistic morphologies and parametric profiles on the order of (6.9 ± 0.6)×10-3 for a realistic magnitude-Sérsic index distribution. Moreover, we find clear detection bias differences between full image scenes simulated with parametric and realistic galaxies, leading to a bias difference of (4.0 ± 0.9)×10-3 independent of the shape measurement method. This makes complex morphology relevant for stage IV weak lensing surveys, exceeding the full error budget of the Euclid Wide Survey (Δμ1,2 < 2 × 103).
Synthesis and NO2 sensing characteristics of Mg-functionalized VO2(M) Nanorods
(Elsevier Ltd, 2025) Mabakachaba, Boitumelo Mafalo; Halindintwali, Sylvain; Numan, Nagla
Herein, we report the synthesis, characterization, and potential NO2 gas sensing application of pristine and Mg-doped VO2(M) nanorods sensors. The gas sensing properties of both sensors were tested for various analytes, i.e., CO, CH4, H2S, NO2, SO2 while varying operating temperatures. The sensors demonstrated substantial sensing performance at working temperature of about 120°C, where VO2-Mg outperformed the pristine sensor with a response value of about 59.3%. At ambient temperature (∼25°C), the response values for pristine and VO2-Mg were 3.29% and 6.35%, respectively. The Mg-dopant's catalytic activity alters the electrical characteristics and adsorbed oxygen species on the sensor surface, leading to improved sensing performance. VO2(M)-based sensor‘s sensing mechanism fits the Freundlich isotherm model, thus making the sensors suitable for detecting NO2 at high and ambient temperatures.
Damping mechanism of the isoscalar giant monopole resonance in 58Ni
(Elsevier B.V, 2025) Mabika, Phumzile Zandile; Bahini ATriambak, Smarajit; Rebeiro, Bernadette
Following the success achieved in explaining the origin of fine structure observed in the isoscalar giant quadrupole resonance (ISGQR) and the isovector giant dipole resonance (IVGDR), fine structure in the region of the isoscalar giant monopole resonance (ISGMR) were investigated using the wavelet analysis in order to investigate the role of different mechanisms contributing to its decay width. In this context, high-energy resolution ISGMR data on many nuclei were acquired at the iThemba Laboratory for Accelerator Based Sciences (iThemba LABS). The experimental scales extracted from these data are compared to different theoretical approaches performed in the framework of quasiparticle random phase approximation (QRPA) and beyond-QRPA including complex configurations using both non-relativistic and relativistic density functional theory. The role of Landau fragmentation was highlighted while the inclusion of coupling between one particle-one hole (1p-1h) and two particle-two hole (2p-2h) configurations modify the strength distributions and wavelet scales indicating the importance of the spreading width.
Euclid preparation: LXVI. Impact of line-of-sight projections on the covariance between galaxy cluster multi-wavelength observable properties: Insights from hydrodynamic simulations
(EDP Sciences, 2025) Karagiannis, Dionysios; Ragagnin, Antonio; Saro, Alex
Context. Cluster cosmology can benefit from combining multi-wavelength studies. In turn, these studies benefit from a characterisation of the correlation coefficients among different mass-observable relations. Aims. In this work, we aim to provide information on the scatter, skewness, and covariance of various mass-observable relations in galaxy clusters in cosmological hydrodynamic simulations. This information will help future analyses improve the general approach to accretion histories and projection effects, as well as to model mass-observable relations for cosmology studies. Methods. We identified galaxy clusters in Magneticum Box2b simulations with masses of M200c > 1014 M⊙ at redshifts of z = 0.24 and z = 0.90. Our analysis included Euclid-derived properties such as richness, stellar mass, lensing mass, and concentration. Additionally, we investigated complementary multi-wavelength data, including X-ray luminosity, integrated Compton-y parameter, gas mass, and temperature. We then examined the impact of projection effects on mass-observable residuals and correlations. Results. We find that at intermediate redshift (z = 0.24), projection effects have the greatest impact of lensing concentration, richness, and gas mass in terms of the scatter and skewness of the log-residuals of scaling relations. The contribution of projection effects can be significant enough to boost a spurious hot-versus cold-baryon correlations and consequently hide underlying correlations due to halo accretion histories. At high redshift (z = 0.9), the richness has a much lower scatter (of log-residuals), while the quantity that is most impacted by projection effects is the lensing mass. The lensing concentration reconstruction, in particular, is affected by deviations of the reduced-shear profile shape from that derived using a Navarro-Frenk-White (NFW) profile; the amount of interlopers in the line of sight, on the other hand, is not as important.
Euclid preparation: LX. the use of HST images as input for weak-lensing image simulations
(EDP Sciences, 2025) Karagiannis, Dionysios; Scognamiglio, Diana; Schrabback, Tim
Data from the Euclid space telescope will enable cosmic shear measurements to be carried out with very small statistical errors, necessitating a corresponding level of systematic error control. A common approach to correct for shear biases involves calibrating shape measurement methods using image simulations with known input shear. Given their high resolution, galaxies observed with the Hubble Space Telescope (HST) can, in principle, be utilised to emulate Euclid observations of sheared galaxy images with realistic morphologies. In this work, we employ a GalSim-based testing environment to investigate whether uncertainties in the HST point spread function (PSF) model or in data processing techniques introduce significant biases in weak-lensing (WL) shear calibration. We used single Sérsic galaxy models to simulate both HST and Euclid observations. We then 'Euclidised' our HST simulations and compared the results with the directly simulated Euclid-like images. For this comparison, we utilised a moment-based shape measurement algorithm and galaxy model fits. Through the Euclidisation procedure, we e_ectively reduced the residual multiplicative biases in shear measurements to sub-percent levels. This achievement was made possible by employing either the native pixel scales of the instruments, utilising the Lanczos15 interpolation kernel, correcting for noise correlations, and ensuring consistent galaxy signal-to-noise ratios between simulation branches. Alternatively, a finer pixel scale can be employed alongside deeper HST data. However, the Euclidisation procedure requires further analysis on the impact of the correlated noise, to estimate calibration bias. We found that additive biases can be mitigated by applying a post-deconvolution isotropisation in the Euclidisation set-up. Additionally, we conducted an in-depth analysis of the accuracy of TinyTim HST PSF models using star fields observed in the F606W and F814W filters. We observe that F606W images exhibit a broader scatter in the recovered best-fit focus, compared to those in the F814W filter. Estimating the focus value for the F606W filter in lower stellar density regimes has allowed us to reveal significant statistical uncertainties
Towards lifetime measurement of excited states in 120Sn using thermal neutron capture
(Elsevier B.V., 2025) Garrett, Paul; Wu, Frank; Andreoiu, Corina
The intruder bands in Sn isotopes, based on the 2p-2h excitation across the Z=50 proton shell gap, are well-known to exhibit shape coexistence near the neutron mid-shell region. The spectroscopic signatures are enhanced E0 transitions between the 0+ band heads and enhanced E2 transitions within rotational bands built on these 0+ band heads. However, lifetime information for the excited 0+ states is incomplete. Experimental details for the neutron-capture reaction and analysis procedures are described, and the first result of the 21+ lifetime demonstrates proper calibration of the setup.
Constraining primordial non-Gaussianity by combining photometric galaxy and 21 cm intensity mapping surveys
(Springer Nature, 2025) Kopana, Mponeng; Maartens, Roy; Jolicoeur, Sheean
The fluctuations produced during cosmic inflation may exhibit non-Gaussian characteristics that are imprinted in the large-scale structure of the Universe. This non-Gaussian imprint is an ultra-large scale signal that can be detected using the power spectrum. We focus on the local-type non-Gaussianity fNL and employ a multi-tracer analysis that combines different probes in order to mitigate cosmic variance and maximize the non-Gaussian signal. In our previous paper, we showed that combining spectroscopic galaxy surveys with 21 cm intensity mapping surveys in interferometer mode could lead to a ∼ 20–30% improvement in the precision on this non-Gaussian signal. Here we combine the same 21 cm experiments, including also single-dish surveys, with photometric galaxy surveys. The 21 cm single-dish surveys are based on MeerKAT and SKAO and the interferometric surveys are alike to HIRAX and PUMA. We implement foreground-avoidance filters and utilize models for the 21 cm thermal noise associated with single-dish and interferometer modes. The photometric galaxy surveys are similar to the DES and LSST. Our multi-tracer Fisher forecasts show a better precision for the combination of the photometric galaxy surveys and 21 cm interferometric surveys than with the 21 cm single-dish surveys – leading to at most an improvement of 23% in the former case and 16% in the latter case. Furthermore, we examine the impact of varying the foreground filter parameter, redshift range and sky area on the derived constraint. We find that the fNL constraint is highly sensitive to both the redshift range and sky area. The foreground filter parameter shows negligible effect.
The tracking tapered gridded estimator for the 21-cm power spectrum from MWA drift scan observations-II. the missing frequency channels
(Oxford University Press, 2025) Chatterjee, Suman; Elahi, Khandakar Md Asif; Bharadwaj, Somnath
Missing frequency channels pose a problem in estimating the redshifted 21-cm power spectrum from radio-interferometric visibility data. This is particularly severe for the Murchison Widefield Array (MWA), which has a periodic pattern of missing channels that introduces spikes along. The Tracking Tapered Gridded Estimator (TTGE) overcomes this by first correlating the visibilities in the frequency domain to estimate the multifrequency angular power spectrum (MAPS) that has no missing frequency separation. We perform a Fourier transform along to estimate. Simulations demonstrate that the TTGE can estimate without any artefacts due to missing channels. However, the spikes persist for the actual foreground-dominated data. A detailed investigation, considering both simulations and actual data, reveals that the spikes originate from a combination of the missing channels and the strong spectral dependence of the foregrounds. We propose and demonstrate a technique to mitigate the spikes. Applying this, we find the values of in the region and 0.35 \, {\rm Mpc^{-1}}$]]> to be consistent with zero within the expected statistical fluctuations. We obtain the upper limit of at for the mean-squared brightness temperature fluctuations of the epoch of reionization (EoR) 21-cm signal. This upper limit is from min of observation for a single pointing direction. We expect tighter constraints when we combine all 162 different pointing directions of the drift scan observation.

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