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Euclid. III. The NISP Instrument
No full textInternational audienceThe Near-Infrared Spectrometer and Photometer (NISP) on board the Euclid satellite provides multiband photometry and R>=450 slitless grism spectroscopy in the 950-2020nm wavelength range. In this reference article we illuminate the background of NISP's functional and calibration requirements, describe the instrument's integral components, and provide all its key properties. We also sketch the processes needed to understand how NISP operates and is calibrated, and its technical potentials and limitations. Links to articles providing more details and technical background are included. NISP's 16 HAWAII-2RG (H2RG) detectors with a plate scale of 0.3" pix^-1 deliver a field-of-view of 0.57deg^2. In photo mode, NISP reaches a limiting magnitude of ~24.5AB mag in three photometric exposures of about 100s exposure time, for point sources and with a signal-to-noise ratio (SNR) of 5. For spectroscopy, NISP's point-source sensitivity is a SNR = 3.5 detection of an emission line with flux ~2x10^-16erg/s/cm^2 integrated over two resolution elements of 13.4A, in 3x560s grism exposures at 1.6 mu (redshifted Ha). Our calibration includes on-ground and in-flight characterisation and monitoring of detector baseline, dark current, non-linearity, and sensitivity, to guarantee a relative photometric accuracy of better than 1.5%, and relative spectrophotometry to better than 0.7%. The wavelength calibration must be better than 5A. NISP is the state-of-the-art instrument in the NIR for all science beyond small areas available from HST and JWST - and an enormous advance due to its combination of field size and high throughput of telescope and instrument. During Euclid's 6-year survey covering 14000 deg^2 of extragalactic sky, NISP will be the backbone for determining distances of more than a billion galaxies. Its NIR data will become a rich reference imaging and spectroscopy data set for the coming decades
Beyond the horizon: Quantifying the full sky foreground wedge in the cylindrical power spectrum
No full textInternational audienceOne of the main obstacles preventing the detection of the redshifted 21-cm signal from neutral hydrogen in the early Universe is the astrophysical foreground emission, which is several orders of magnitude brighter than the signal. The foregrounds, due to their smooth spectra, are expected to predominantly occupy a region in the cylindrical power spectrum known as the foreground wedge. However, the conventional equations describing the extent of the foreground wedge are derived under a flat-sky approximation. This assumption breaks down for tracking wide-field instruments, thus rendering these equations inapplicable in these situations. In this paper, we derive equations for the full sky foreground wedge and show that the foregrounds can potentially extend far beyond what the conventional equations suggest. We also derive the equations that describe a specific bright source in the cylindrical power spectrum space. The validity of both sets of equations is tested against numerical simulations. Many current and upcoming interferometers (e.g., LOFAR, NenuFAR, MWA, SKA) are wide-field phase-tracking instruments. These equations give us new insights into the nature of foreground contamination in the cylindrical power spectra estimated using wide-field instruments. Additionally, they allow us to accurately associate features in the power spectrum to foregrounds or instrumental effects. The equations are also important for correctly selecting the "EoR window" for foreground avoidance analyses, and for planning 21-cm observations. In future analyses, it is recommended to use these updated horizon lines to indicate the foreground wedge in the cylindrical power spectrum accurately. The new equations for generating the updated wedge lines are made available in a Python library, pslines
Distributional Regression U-Nets for the Postprocessing of Precipitation Ensemble Forecasts
No full textInternational audienceAccurate precipitation forecasts have a high socio-economic value due to their role in decision-making in various fields such as transport networks and farming. We propose a global statistical postprocessing method for grid-based precipitation ensemble forecasts. This U-Net-based distributional regression method predicts marginal distributions in the form of parametric distributions inferred by scoring rule minimization. Distributional regression U-Nets are compared to state-of-the-art postprocessing methods for daily 21-h forecasts of 3-h accumulated precipitation over the South of France. Training data comes from the Météo-France weather model AROME-EPS and spans 3 years. A practical challenge appears when consistent data or reforecasts are not available. Distributional regression U-Nets compete favorably with the raw ensemble. In terms of continuous ranked probability score, they reach a performance comparable to quantile regression forests (QRF). However, they are unable to provide calibrated forecasts in areas associated with high climatological precipitation. In terms of predictive power for heavy precipitation events, they outperform both QRF and semi-parametric QRF with tail extension
Euclid preparation. Sensitivity to non-standard particle dark matter model
No full textInternational audienceThe Euclid mission of the European Space Agency will provide weak gravitational lensing and galaxy clustering surveys that can be used to constrain the standard cosmological model and its extensions, with an opportunity to test the properties of dark matter beyond the minimal cold dark matter paradigm. We present forecasts from the combination of these surveys on the parameters describing four interesting and representative non-minimal dark matter models: a mixture of cold and warm dark matter relics; unstable dark matter decaying either into massless or massive relics; and dark matter experiencing feeble interactions with relativistic relics. We model these scenarios at the level of the non-linear matter power spectrum using emulators trained on dedicated N-body simulations. We use a mock Euclid likelihood to fit mock data and infer error bars on dark matter parameters marginalised over other parameters. We find that the Euclid photometric probe (alone or in combination with CMB data from the Planck satellite) will be sensitive to the effect of each of the four dark matter models considered here. The improvement will be particularly spectacular for decaying and interacting dark matter models. With Euclid, the bounds on some dark matter parameters can improve by up to two orders of magnitude compared to current limits. We discuss the dependence of predicted uncertainties on different assumptions: inclusion of photometric galaxy clustering data, minimum angular scale taken into account, modelling of baryonic feedback effects. We conclude that the Euclid mission will be able to measure quantities related to the dark sector of particle physics with unprecedented sensitivity. This will provide important information for model building in high-energy physics. Any hint of a deviation from the minimal cold dark matter paradigm would have profound implications for cosmology and particle physics
A depth-averaged model for granular flow consistent with the incompressible µ(I) rheology
No full textInternational audienceWe derive a depth-averaged model consistent with the µ(I) rheology for an incompressible granular flow down an inclined plane. The first two variables of the model are the depth and the depth-averaged velocity. The shear is also taken into account via a third variable called enstrophy. The obtained system is a hyperbolic system of conservation laws, with an additional equation for the energy. The system is derived from an asymptotic expansion of the flow variables in powers of the shallow-water parameter. This method ensures that the model is fully consistent with the rheology. The velocity profile is a Bagnold profile at leading order and the first-order correction to this profile can be calculated for flows that are not steady uniform. The first-order correction to the classical granular friction law is also consistently written. As a consequence, the instability threshold of the steady uniform flow is the same for the depth-averaged model and for the governing equations. In addition, a higher-order version that contains diffusive terms is also presented. The spatial growth rate, the phase velocity and the cutoff frequency of the version with diffusion are in good agreement with the experimental data and with the theoretical predictions for the rheology. The mathematical structure of the equations enables to use well-known and stable numerical solvers. Numerical simulations of granular roll waves are presented. The model has the same limitations as the µ(I) rheology, in particular for the solid/ liquid and liquid/gas transitions, and needs therefore a regularization for these transitions
Best of both worlds: Fusing hyperspectral data from two generations of spectro-imagers for X-ray astrophysics
No full textInternational audienceWith the launch of the X-Ray Imaging and Spectroscopy Mission (XRISM) and the advent of microcalorimeter detectors, X-ray astrophysics is entering in a new era of spatially resolved high resolution spectroscopy. But while this new generation of X-ray telescopes have much finer spectral resolutions than their predecessors (e.g. XMM-Newton, Chandra), they also have coarser spatial resolutions, leading to problematic cross-pixel contamination. This issue is currently a critical limitation for the study of extended sources such as galaxy clusters of supernova remnants. To increase the scientific output of XRISM's hyperspectral data, we propose to fuse it with XMM-Newton data, and seek to obtain a cube with the best spatial and spectral resolution of both generations. This is the aim of hyperspectral fusion. In this article, we have implemented an algorithm that jointly deconvolves the spatial response of XRISM and the spectral response of XMM-Newton. To do so, we construct a forward model adapted for instrumental systematic degradations and Poisson noise, then tackle hyperspectral fusion as a regularized inverse problem. We test three methods of regularization: low rank approximation with Sobolev regularization; low rank approximation with 2D wavelet sparsity ; and 2D-1D wavelet sparsity. We test our method on toy models constructed from hydrodynamic simulations of supernova remnants. We find that our method reconstructs the ground truth well even when the toy model is complex. For the regularization term, we find that while the low rank approximation worked well as a spectral denoiser in models with less spectral variability, it introduced a bias in models with more spectral variability, in which case the 2D-1D wavelet sparsity regularization worked best. After demonstrating a proof of concept in this article, we aim to apply this method to real X-ray astrophysical data in the near future
Mercury trophic transfer and biomagnification in food webs within a tropical embayment as evidenced by nitrogen and carbon stable isotope analysis
No full textInternational audienceMercury (Hg) contamination in marine ecosystems poses a significant environmental threat due to its high toxicity, persistence in the environment, and tendency to bioaccumulate in organisms and biomagnify in food webs. Understanding how Hg moves through these food webs is essential for assessing its ecological and health impacts. To investigate the trophic dynamics of Hg in Rayong Bay, Gulf of Thailand, we collected marine organisms from the pelagic and benthic food webs during 2022–2023 and analyzed the total mercury content (THg) in plankton (phytoplankton, zooplankton, and fish larvae) and in 81 marine animal species. Furthermore, the stable nitrogen and carbon isotope values (δ15N and δ13C) were measured to establish their trophic levels (TLs) and potential food sources in the food web. Based on these analyses, we calculated the biomagnification factor using TL-adjusted ratios (BMFnorm) and trophic magnification factor (TMF) for the different TLs. BMFnorm values exceeded 1.0 in over 40 % of cases for both the pelagic and benthic food webs, indicating THg biomagnification from prey to predator. Notably, the pelagic food web exhibited a markedly higher TMF value (TMF = 6.68) compared to that of the benthic food web (TMF = 2.06), suggesting stronger Hg biomagnification within the pelagic food web. Our findings also highlight the consumption risk of Hg in some fish species in the Rayong Bay food webs, emphasizing the need for continued monitoring and mitigation strategies to safeguard both human and ecological health
Fatty acid response of calcifying benthic Antarctic species to ocean acidification and warming
No full textInternational audienceOcean acidification (OA) and ocean warming (OW) are likely to alter the biochemical composition of certain organisms as a physiological response to these changing environmental conditions. Given the importance of fatty acids (FA) in energy transfer within marine food webs, this two-month laboratory study examines the response of two calcifying species from Potter Cove (Antarctica) - the bivalve Aequiyoldia eightsii and the coral Malacobelemnon daytoni - to predicted OA and OW, focusing on their FA profiles. Neither species showed significant changes compared to the control group in the composition of FA ratios associated with immune function and cell membrane fluidity in response to either OA or OW. Additionally, the FA composition related to inflammatory responses remained largely unaffected by the stressors, although the 20:5n-3 FA was negatively impacted in A. eightsii under high-temperature conditions. Overall, the FA composition in these species appears robust to near-future environmental changes
Des données géologiques à l’expérience des atmosphères primitives
No full textInternational audienceL’enjeu était de faire sentir que l’air que nous respirons est relativement récent au regard de l’histoire de la Terre (16 millions d’années). Il s’agissait de montrer le caractère intuitivement choquant entre le temps long des processus géologiques de la Terre et la rapidité des modifications qu’entraînent les activités humaines sur le climat, depuis 2,5 siècles. Mais surtout, il était question de faire respirer l’air, sa préciosité et son histoire. Ainsi, la démarche de création s'est effectuée en étroite collaboration avec des chercheur.e.s en sciences de la Terre. Les données recueillies ont été traduites, puis interprétées par l’équipe artistique pour les transmettre au public à travers un dispositif artistique et par un dispositif plus didactique. Dans un espace dit “sensible” nous avons cherché à retracer, par l’immersion sensorielle (sons, odeurs,lumière, sable…) la traversée de ces temps géologiques, afin de prendre conscience du fragile équilibre des conditions qui permettent de rendre respirable l’air que nous respirons. Ce dispositif sensible invitait le spectateur à vivre l’expérience des atmosphères pré- et post- anthropocènes, marquées par leur irrespirabilité pour les humains. Par ailleurs, l’exposition dans ce lieu destiné ni à la science, ni à l’art, avait une autre vocation, celle de transmettre au public divers les données et informations collectées lors d’échanges pluridisciplinaires, permettant de partager les hypothèses sur les scénarios passés et futurs des atmosphères. Ainsi, nous avons recréé plusieurs compositions atmosphériques qui ont recouvert la Terre. Nous avons aussi expliciter les différentes périodes et transformations terrestres comme les cycles de glaciation ou les fluctuations de l’oxygène par des dispositifs sensoriels à manipuler. En matérialisant l'irrespirabilité des premières atmosphères terrestres, l'exposition invitait à expérimenter une réalité inconnue, anhistorique, questionnant notre impact sur la planète, pour des millions d’années à venir