HAL-CEA
Not a member yet
145450 research outputs found
Sort by
Deriving accurate galaxy cluster masses using X-ray thermodynamic profiles and graph neural networks
No full textInternational audiencePrecise determination of galaxy cluster masses is crucial for establishing reliable mass-observable scaling relations in cluster cosmology. We employ graph neural networks (GNNs) to estimate galaxy cluster masses from radially sampled profiles of the intra-cluster medium (ICM) inferred from X-ray observations. GNNs naturally handle inputs of variable length and resolution by representing each ICM profile as a graph, enabling accurate and flexible modeling across diverse observational conditions. We trained and tested GNN model using state-of-the-art hydrodynamical simulations of galaxy clusters from The Three Hundred Project. The mass estimates using our method exhibit no systematic bias compared to the true cluster masses in the simulations. Additionally, we achieve a scatter in recovered mass versus true mass of about 6%, which is a factor of six smaller than obtained from a standard hydrostatic equilibrium approach. Our algorithm is robust to both data quality and cluster morphology and it is capable of incorporating model uncertainties alongside observational uncertainties. Finally, we apply our technique to XMM-Newton observed galaxy cluster samples and compare the GNN derived mass estimates with those obtained with -M scaling relations. Our results provide strong evidence, at 5 level, for a mass-dependent bias in SZ derived masses, with higher mass clusters exhibiting a greater degree of deviation. Furthermore, we find the median bias to be , albeit with significant dispersion due to its mass dependence. This work takes a significant step towards establishing unbiased observable mass scaling relations by integrating X-ray, SZ and optical datasets using deep learning techniques, thereby enhancing the role of galaxy clusters in precision cosmology
Flux-driven turbulent transport using penalisation in the Hasegawa-Wakatani system
No full textInternational audienceFirst numerical results from the newly developed pseudo-spectral code P-FLARE (Penalised FLux-driven Algorithm for REduced models) are presented. This flux-driven turbulence/transport code uses a pseudo-spectral formulation with the penalisation method to impose radial boundary conditions. Its concise, flexible structure allows implementing various quasi-two-dimensional reduced fluid models in flux-driven formulation. Here, results from simulations of the modified Hasegawa–Wakatani system are discussed, where particle transport and zonal flow formation, together with profile relaxation, are studied. It is shown that coupled spreading/profile relaxation that one obtains for this system is consistent with a simple one-dimensional model of coupled spreading/transport equations. Then, the effect of a particle source is investigated, which results in the observation of sandpile-like critical behaviour. The model displays profile stiffness for certain parameters, with very different input fluxes resulting in very similar mean density gradients. This is due to different zonal flow levels around the critical value for the control parameter (i.e. the ratio of the adiabaticity parameter to the mean gradient) and the existence for this system of a hysteresis loop for the transition from two-dimensional turbulence to a zonal flow dominated state
Early-life drift mechanism investigation of 150nm GaN-on-SiC HEMT RF under accelerated DC test
No full textInternational audienceThis work investigates the initial electrical parameter drift in 150 nm gate-length GaN-on-SiC HEMTs subjected to DC high-temperature operating life stress for up to 96 hours at multiple baseplate temperatures. Junction temperature was estimated to assess the actual operating temperature of the device under stress conditions. A transient current IDS drift was observed, evolving differently with temperature. Electrical characterizations revealed threshold voltage shifts associated with trap dynamics. Drain-lag (DL) increased while gate-lag (GL) remained stable, indicating a dominant role of buffer traps over surface effects. Schottky diode analysis showed no significant gate degradation, suggesting that bulk-related trapping mechanisms are the main contributors to electrical shift
Discovery of suppressed charged-particle production in ultrarelativistic oxygen-oxygen collisions
No full textInternational audienceA hot and dense state of nuclear matter, known as the quark-gluon plasma, is created in collisions of ultrarelativistic heavy nuclei. Highly energetic quarks and gluons, collectively referred to as partons, lose energy as they travel through this matter, leading to suppressed production of particles with large transverse momenta (). Conversely, high- particle suppression has not been seen in proton-lead collisions, raising questions regarding the minimum system size required to observe parton energy loss. Oxygen-oxygen (OO) collisions examine a region of effective system size that lies between these two extreme cases. The CMS detector at the CERN LHC has been used to quantify charged-particle production in inclusive OO collisions for the first time via measurements of the nuclear modification factor (). The is derived by comparing particle production to expectations based on proton-proton (pp) data and has a value of unity in the absence of nuclear effects. The data for OO and pp collisions at a nucleon-nucleon center-of-mass energy = 5.36 TeV correspond to integrated luminosities of 6.1 nb and 1.02 pb, respectively. The is below unity with a minimum of 0.69 0.04 around = 6 GeV. The data exhibit better agreement with theoretical models incorporating parton energy loss as compared to baseline models without energy loss
Cleaning Galactic foregrounds with spatially varying spectral dependence from CMB observations with \texttt{fgbuster}
No full textInternational audienceIn the context of maximum-likelihood parametric component separation for next-generation full-sky CMB polarization experiments, we study the impact of fitting different spectral parameters of Galactic foregrounds in distinct subsets of pixels on the sky, with the goal of optimizing the search for primordial B modes. Using both simulations and analytical arguments, we highlight how the post-component separation uncertainty and systematic foreground residuals in the cleaned CMB power spectrum depend on spatial variations in the spectral parameters. We show that allowing spectral parameters to vary across subsets of the sky pixels is essential to achieve competitive S/N on the reconstructed CMB after component separation while keeping residual foreground bias under control. Although several strategies exist to define pixel subsets for the spectral parameters, each with its advantages and limitations, we show using current foreground simulations in the context of next-generation space-borne missions that there are satisfactory configurations in which both statistical and systematic residuals become negligible. The exact magnitude of these residuals, however, depends on the mission's specific characteristics, especially its frequency coverage and sensitivity. We also show that the post-component separation statistical uncertainty is only weakly dependent on the properties of the foregrounds and propose a semi-analytical framework to estimate it. On the contrary, the systematic foreground residuals highly depend on both the properties of the foregrounds and the chosen spatial resolution of the spectral parameters
Euclid Quick Data Release (Q1). A first view of the star-forming main sequence in the Euclid Deep Fields
No full textInternational audienceThe star-forming main sequence (SFMS) is a tight relation observed between stellar masses and star formation rates (SFR) in a population of galaxies. This relation is observed at different redshifts, in various morphological, and environmental domains, and is key to understanding the underlying relations between a galaxy budget of cold gas and its stellar content. Euclid Quick Data Release 1 (Q1) gives us the opportunity to investigate this fundamental relation in galaxy formation and evolution. We complement the Euclid release with public IRAC observations of the Euclid Deep Fields, improving the quality of recovered photometric redshifts, stellar masses, and SFRs, as is shown both with simulations and a comparison with available spectroscopic redshifts. From Q1 data alone, we recover more than galaxies with , giving a precise constraint of the SFMS at the high-mass end. We investigated the SFMS, in a redshift interval between and , comparing our results with the existing literature and fitting them with a parameterisation taking into account the presence of a bending of the relation at the high-mass end, depending on the bending mass, . We find good agreement with previous results in terms of values, and an increasing trend for the relation scatter at higher stellar masses. We also investigate the distribution of physical (e.g. dust absorption, , and formation age) and morphological properties (e.g., Sérsic index and radius) in the SFR--stellar mass plane, and their relation with the SFMS. These results highlight the potential of Euclid in studying the fundamental scaling relations that regulate galaxy formation and evolution in anticipation of the forthcoming Data Release 1
Euclid Quick Data Release (Q1). Extending the quest for little red dots to z<4
No full textInternational audienceRecent James Webb Space Telescope (JWST) observations have revealed a population of sources with a compact morphology and a `v-shaped' continuum, namely blue at rest-frame A and red at longer wavelengths. The nature of these sources, called `little red dots' (LRDs), is still debated, since it is unclear if they host active galactic nuclei (AGN) and their number seems to drastically drop at z<4. We utilise the 63 covered by the quick Euclid Quick Data Release (Q1) to extend the search for LRDs to brighter magnitudes and to lower z than what has been possible with JWST to have a broader view of the evolution of this peculiar galaxy population. The selection is done by fitting the available photometric data (Euclid, Spitzer/IRAC, and ground-based griz data) with two power laws, to retrieve the rest-frame optical and UV slopes consistently over a large redshift range (i.e, z<7.6). We exclude extended objects and possible line emitters, and perform a visual inspection to remove imaging artefacts. The final selection includes 3341 LRD candidates from z=0.33 to z=3.6, with 29 detected in IRAC. Their rest-frame UV luminosity function, in contrast with previous JWST studies, shows that the number density of LRD candidates increases from high-z down to z=1.5-2.5 and decreases at even lower z. Less evolution is apparent focusing on the subsample of more robust LRD candidates having IRAC detections, which is affected by low statistics and limited by the IRAC resolution. The comparison with previous quasar UV luminosity functions shows that LRDs are not the dominant AGN population at z<4. Follow-up studies of these LRD candidates are key to confirm their nature, probe their physical properties and check for their compatibility with JWST sources, since the different spatial resolution and wavelength coverage of Euclid and JWST could select different samples of compact sources
Euclid Quick Data Release (Q1) First study of red quasars selection
No full textInternational audienceRed quasars constitute an important but elusive phase in the evolution of supermassive black holes, where dust obscuration can significantly alter their observed properties. They have broad emission lines, like other quasars, but their optical continuum emission is significantly reddened, which is why they were traditionally identified based on near- and mid-infrared selection criteria. This work showcases the capability of the \Euclid space telescope to find a large sample of red quasars, using \Euclid near infrared (NIR) photometry. We first conduct a forecast analysis, comparing a synthetic catalogue of red QSOs with COSMOS2020. Using template fitting, we reconstruct \Euclid-like photometry for the COSMOS sources and identify a sample of candidates in a multidimensional colour-colour space achieving completeness for mock red QSOs with contaminants. To refine our selection function, we implement a probabilistic Random Forest classifier, and use UMAP visualisation to disentangle non-linear features in colour-space, reaching completeness and purity. A preliminary analysis of the candidates in the \Euclid Deep Field Fornax (EDF-F) shows that, compared to VISTA+DECAm-based colour selection criteria, \Euclid's superior depth, resolution and optical-to-NIR coverage improves the identification of the reddest, most obscured sources. Notably, the \Euclid exquisite resolution in the filter unveils the presence of a candidate dual quasar system, highlighting the potential for this mission to contribute to future studies on the population of dual AGN. The resulting catalogue of candidates, including more the 150 000 sources, provides a first census of red quasars in \Euclid Q1 and sets the groundwork for future studies in the Euclid Wide Survey (EWS), including spectral follow-up analyses and host morphology characterisation
Experimentation of an autonomous solar cold room with thermal emulation of virtual food storage
No full textInternational audienceThe development of autonomous solar cold rooms faces challenges in regions with abundant solar resources but limited electrical grid infrastructure. Key issues include reliable energy storage, efficient refrigeration, and system portability for agricultural goods storage. Previous studies often neglected the dynamic temperature evolution of stored goods, crucial for food preservation. CEA and AIRWELL collaborated to design and test a Cold Room Solar Autonomous (CFSA) system prototype. The CFSA system includes a lead-acid battery, a 4 kWth refrigeration unit, a configurable PV field with 20x 500 Wpeak PV modules, an 8000 VA DC/AC inverter, DC MPPT chargers, and a cold room connected to a backup electrical network. CEA developed an emulation method of the actual internal thermal load for such system test, under dynamic conditions to maintain food temperatures, using heating resistors controlled by a dynamic thermal simulation. Testing on the CEA platform from August to November 2024 included various sensors and controllers while the Scilab models and simulation of the thermal mass provided performance insights. The battery maintained continuous refrigeration with 32 hours of autonomy without solar input during virtual matter’s temperature drop phase. The PV field ensured operational autonomy with 3kWh/kWc/day under reduced sunshine, requiring a backup source approximately every 3 days under low sunshine and temperature difference conditions. The experimental methodology developed in this work opens further development perspective of the CFSA hybrid micro plant to support the local grid balance by adjusting its energy storage and consumption in response to grid operators' signals. The estimated flexibility is about 1%/t.K referring to the CFSA system nominal power consumption, food mass stored and ind/out temperature difference
Open-Loop Paralleling of Class E2 resonant DC-DC Converters
No full textInternational audienceIn view of investigating new strategies to cope with the limitation of high output power of very high frequency power converters, this paper describes the implementation of Class E2 parallel resonant DC-DC converters which is suitable candidate topology for the experiment as it can maintain ZVS over a wide load range naturally in open-loop. Consequently, several 10W elementary prototypes were gathered which maintain an overall efficiency >80% for a load range variation of 2-10W at a switching frequency of 10MHz. Subsequently, multiple paralleling configurations are investigated experimentally which allowed the construction of a predictive model for untested parallel converter configurations. A maximum output power of 42.78W was achieved with 5 parallel converters.