HAL-OBSPM
Not a member yet
37663 research outputs found
Sort by
Euclid preparation: The flat-sky approximation for the clustering of Euclid's photometric galaxies
No full textInternational audienceWe compare the performance of the flat-sky approximation and Limber approximation for the clustering analysis of the photometric galaxy catalogue of Euclid. We study a 6 bin configuration representing the first data release (DR1) and a 13 bin configuration representative of the third and final data release (DR3). We find that the Limber approximation is sufficiently accurate for the analysis of the wide bins of DR1. Contrarily, the 13 bins of DR3 cannot be modelled accurately with the Limber approximation. Instead, the flat-sky approximation is accurate to below in recovering the angular power spectra of galaxy number counts in both cases and can be used to simplify the computation of the full power spectrum in harmonic space for the data analysis of DR3
Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine C: Finding lenses with machine learning
No full textInternational audienceStrong gravitational lensing has the potential to provide a powerful probe of astrophysics and cosmology, but fewer than 1000 strong lenses have been confirmed so far. With a resolution covering a third of the sky, the Euclid telescope will revolutionise the identification of strong lenses, with lenses forecasted to be discovered amongst the 1.5 billion galaxies it will observe. We present an analysis of the performance of five machine-learning models at finding strong gravitational lenses in the quick release of Euclid data (Q1) covering 63,deg^2. The models have been validated by citizen scientists and expert visual inspection. We focus on the best-performing network: a fine-tuned version of the Zoobot pretrained model originally trained to classify galaxy morphologies in heterogeneous astronomical imaging surveys. Of the one million Q1 objects that Zoobot was tasked to find strong lenses within, the top 1000 ranked objects contain 122 grade A lenses (almost-certain lenses) and 41 grade B lenses (probable lenses). A deeper search with the five networks combined with visual inspection yielded 250 (247) grade A (B) lenses, of which 224 (182) are ranked in the top by Zoobot . When extrapolated to the full Euclid survey, the highest ranked one million images will contain grade A or B strong gravitational lenses.</jats:p
Simulated parametric study of coherent differential imaging for exoplanet detection with SPHERE
No full textInternational audienceMotivations: Classical high-contrast imaging (ADI, RDI,…) always requires extensive observation time for speckle calibration. We investigate Coherent Differential Imaging (CDI), a powerful alternative that relies on active, user-controlled modulation rather than passive diversity.Method: We implemented the Pair-Wise Probing algorithm within COMPASS simulations to actively modulate optical aberrations in a VLT/SPHERE-like environment.Results: We performed a comprehensive parametric analysis, demonstrated a contrast gain up to a factor of 11 in simulations and identified distinct corrective regimes.Perspective: This work paves the way for CDI as a highly efficient strategy for next-generation instruments like SPHERE+ and the Roman Space Telescope
Euclid preparation. Decomposing components of the extragalactic background light using multi-band intensity mapping cross-correlations
No full textInternational audienceThe extragalactic background light (EBL) fluctuations in the optical/near-IR encode the cumulative integrated galaxy light (IGL), diffuse intra-halo light (IHL), and high- sources from the epoch of reionisation (EoR), but they are difficult to disentangle with auto-spectra alone. We aim to decompose the EBL into its principal constituents using multi-band intensity mapping combined with cosmic shear and galaxy clustering. We develop a joint halo-model framework in which IHL follows a mass- and redshift-dependent luminosity scaling, IGL is set by an evolving Schechter luminosity function, and EoR emission is modelled with Pop II/III stellar emissivities and a binned star-formation efficiency. Using mock surveys in a flat CDM cosmology with ten spectral bands spanning 0.75-5.0 in the NEP deep fields over about 100 with source detections down to AB=20.5 for masking, and six redshift bins to , we fit auto- and cross-power spectra using a MCMC method. The combined SPHERExEuclid analysis recovers all fiducial parameters within 1 and reduces 1 uncertainties on IHL parameters by 10-35% relative to SPHEREx EBL-only, while EoR star-formation efficiency parameters improve by 20-35%. Cross-correlations reveal a stronger coupling of IHL than IGL to the shear field, enhancing component separation; conversely, the EoR contribution shows negligible correlation with cosmic shear and galaxy clustering, aiding its isolation in the EBL. Relative to the SPHEREx EBL-only case, the inferred IHL fraction as a function of halo mass is significantly tightened over , with uncertainties reduced by 5-30%, and the resulting star-formation rate density constraints extend to , with uncertainty reductions of 22-31%
Benchmark for two-dimensional large scale coherent structures in partially magnetized E × B plasmas—community collaboration & lessons learned
No full textInternational audienceAbstract Low-temperature plasmas (LTPs) are essential to both fundamental scientific research and critical industrial applications. As in many areas of science, numerical simulations have become a vital tool for uncovering new physical phenomena and guiding technological development. Code benchmarking remains crucial for verifying implementations and evaluating performance. This work continues the Landmark benchmark initiative, a series specifically designed to support the verification of LTP codes. In this study, seventeen simulation codes from a collaborative community of nineteen international institutions modeled a partially magnetized E × B Penning discharge. The emergence of large scale coherent structures, or rotating plasma spokes, endows this configuration with an enormous range of time scales, making it particularly challenging to simulate. The codes showed excellent agreement on the rotation frequency of the spoke as well as key plasma properties, including time-averaged ion density, plasma potential, and electron temperature profiles. Achieving this level of agreement came with challenges, and we share lessons learned on how to conduct future benchmarking campaigns. Comparing code implementations, computational hardware, and simulation runtimes also revealed interesting trends, which are summarized with the aim of guiding future plasma simulation software development
Evidence of mutually exclusive outflow forms from a black hole X-ray binary
No full textInternational audienceAccretion onto black holes often leads to the launch of outflows that significantly influence their surrounding environments. The two primary forms of these outflows are X-ray disk winds-hot, ionized gases ejected from the accretion disk-and relativistic jets, which are collimated streams of particles often expelled along the rotational axis of the black hole. While previous studies have revealed a general association between spectral states and different types of outflows, the physical mechanisms governing wind and jet formation remain debated. Here, using coordinated NICER and MeerKAT observations of the recurrent black hole X-ray binary 4U 1630-472, we identify a clear anti-correlation between X-ray disk winds and jets: during three recent outbursts, only one type of outflow is detected at a time. Notably, this apparent exclusivity occurs even as the overall accretion luminosity remains within the range expected for a standard thin disk, characteristic of the canonical soft state. These results suggest a competition between outflow channels that may depend on how the accretion energy is partitioned between the disk and the corona. Our findings provide new observational constraints on jet and wind formation in X-ray binaries and offer a fresh perspective on the interplay between different modes of accretion-driven feedback
Variation du quantum d'action de Planck en Relativité Intriquée
No full textv2. 21 pages. Reorganisation of the structure of the article with respect to v1.International audienceEntangled Relativity is a recent non-linear reformulation of General Relativity that does not include Planck’s constant or Newton’s gravitational constant in its fundamental structure. One of its key predictions is that emerges as a dynamical field, potentially varying across space and time. In this study, we estimate the magnitude of such variations in three different astrophysical environments: the weak gravitational fields of the Sun and Earth, the intermediate regime of white dwarfs, and the strong fields found in neutron stars. In the Solar System, the relative change in is minimal, reaching at most . In white dwarfs, depending on central density, variations range from to . For neutron stars, the variation can be as high as at the surface relative to a remote observer, and up to at the center. These results suggest that, if Entangled Relativity accurately describes gravity, spatial variations of Planck’s constant could become an observable signature, particularly in the context of dense stellar objects
Fuzzy dark matter soliton as gravitational lens
No full textInternational audienceThe Schrödinger-Poisson (SP) equations predict fuzzy dark matter (FDM) solitons. Given the FDM mass , the FDM soliton in the Milky Way is massive but diffuse . Therefore, such FDM soliton can serve as a gravitational lens for gravitational waves (GWs) with frequency . In this paper, we investigate its gravitational lensing effects by numerical simulation of the propagation of GWs through it. We find that the maximum magnification factor of GWs is very small , but the corresponding magnification zone is huge for FDM with mass equal to . Consequently, this small magnification factor compounding over such large magnification zone results in a small antisotropy of over a large solid angle in the GW background. That level of antisotropy is out of the sensitivity, , of the pulsar timing arrays today
Direct multi-model dark-matter search with gravitational-wave interferometers using data from the first part of the fourth LIGO-Virgo-KAGRA observing run
No full textInternational audienceGravitational-wave detectors can probe the existence of dark matter with exquisite sensitivity. Here, we perform a search for three kinds of dark matter -- dilatons (spin-0), dark photons (spin-1) and tensor bosons (spin-2) -- using three independent methods on the first part of the most recent data from the fourth observing run of LIGO--Virgo--KAGRA. Each form of dark matter could have interacted with different standard-model particles in the instruments, causing unique differential strains on the interferometers. While we do not find any evidence for a signal, we place the most stringent upper limits to-date on each of these models. For scalars with masses between eV that couple to photons or electrons, our constraints improve upon those from the third observing run by one order of magnitude, with the tightest limit of at a mass of . For vectors with masses between eV that couple to baryons, our constraints supersede those from MICROSCOPE and Eöt-Wash by one to two orders of magnitude, reaching a minimum of at a mass of eV. For tensors with masses of eV (the full mass range analyzed) that couple via a Yukawa interaction, our constraints surpass those from fifth-force experiments by four to five orders of magnitude, achieving a limit as low as at eV. Our results show that gravitational-wave interferometers have become frontiers for new physics and laboratories for direct multi-model dark-matter detection
Investigating Pulsar Wind Nebula DA 495: Insights from LHAASO and Multi-Wavelength Observations
No full textInternational audiencePulsar wind nebula DA~495 (G65.7+1.2) has been extensively observed from radio to TeV -ray bands. We present LHAASO observations of DA~495, revealing an energy-dependent morphology, where an extended source with is detected by WCDA (0.4-15~TeV), and a point-like source with a 95% upper limit of is observed by KM2A (). The spectrum of the source extends beyond 100~TeV with a break or cutoff at a few tens of TeV. Our X-ray data analysis, based on Chandra and XMM-Newton observations, shows that the X-ray emission of DA~495 extends well to , significantly larger than the size previously reported. The broadband spectral energy distribution across radio, X-ray and TeV -ray bands is phenomenologically described by a one-zone leptonic model, yielding an average magnetic field of 5 , while Fermi-LAT spectral analysis indicates a likely presence of a -ray pulsar within the system. A time-dependent model, in which particle transport is convection-dominated in the inner region (within ) and diffusion-dominated in the outer region, successfully reproduces the observed radial profiles of X-ray surface brightness and spectral index, and also accounts for the TeV -ray emission detected by LHAASO, suggesting that DA~495 represents an evolved PWN with ongoing particle escape that gives rise to a TeV halo component -- that is, a PWN+halo system