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SO 2 , silicate clouds, but no CH 4 detected in a warm Neptune
No full textInternational audienceWASP-107b is a warm (∼740 K) transiting planet with a Neptune-like mass of ∼30.5 M ⊕ and Jupiter-like radius of ∼0.94 R J 1, 2 whose extended atmosphere is eroding 3 . Previous observations showed evidence for water vapour and a thick high-altitude condensate layer in WASP-107b's atmosphere 4, 5 . Recently, photochemically produced sulphur dioxide (SO 2 ) was detected in the atmosphere of a hot (∼1,200 K) Saturn-mass planet from transmission spectroscopy near 4.05 µm 6, 7 , but for temperatures below ∼1,000 K sulphur is predicted to preferably form sulphur allotropes instead of SO 2 8-10 . Here we report the 9σ-detection of two fundamental vibration bands of SO 2 , at 7.35 µm and 8.69 µm, in the transmission spectrum of WASP-107b using the Mid-Infrared Instrument (MIRI) of the JWST. This discovery establishes WASP-107b as the second irradiated exoplanet with confirmed photochemistry, extending the temperature range of exoplanets exhibiting detected photochemistry from ∼1,200 K down to ∼740 K. Additionally, our spectral analysis reveals the presence of silicate clouds, which are strongly favoured (∼7σ) over simpler cloud setups. Furthermore, water is detected (∼12σ), but methane is not. These findings provide evidence of disequilibrium chemistry and indicate a dynamically active atmosphere with a super-solar metallicity. WASP-107b was observed with JWST MIRI on 19 -20 January 2023. The SLITLESS-PRISM subarray of the low-resolution spectrometer was used, offering a spectral resolution rang-(Program identifier (PID) 1280; P.I. P.O. Lagage).</div
The SCM instrument for the ESA Plasma Observatory mission
No full textInternational audienceThe proposal of the Plasma Observatory mission was selected for a competitive phase A with two other missions in the framework of the seventh call for medium mission (M7) organized by ESA. The mission selection is planned in 2026 for a launch in 2037. Its main objectives are to unveil how are particles energized in space plasma and which processes dominate energy transport and drive coupling between the different regions of the terrestrial magnetospheric system? The mission consists of seven satellites, a main platform (mothercraft, MSC) and six smaller identical satellites (daughtercraft) evolving along an equatorial elliptical orbit with an apogee ~17 and a perigee ~8 Earth radii. The seven satellites will fly forming two tetraedra and allowing simultaneous measurements at both fluid and ion scales. The mission will include three key science regions: dayside (solar wind, bow shock, magnetosheath, magnetopause), nightside transition region (quasidipolar region, transient near-Earth current sheet, field-aligned currents, braking flow region) and the medium magnetotail (near-Earth reconnection region, fast flow formation region). Plasma Observatory mission is the next logical step after the four satellite magnetospheric missions Cluster and MMS. The search-coil magnetometer (SCM), strongly inherited of the SCM designed for the ESA JUICE mission, is only included in the Fields instrument suite of the MSC. SCM will be delivered by LPP and LPC2E and will provide the three components of the magnetic field fluctuations in the [0.1Hz-8kHz] frequency range, after digitization by the Low frequency Receiver (LFR) within the Field and Wave Processor (FWP), relevant for the three Key science regions. It will be mounted on a 6m boom and will allow to reach the following sensitivities [10-3, 1.5x10-6, 5x10-9, 10-10, 5x10-10] nT2/Hz at [1, 10, 100, 1000, 8000] Hz. Associated with the electric field instrument (EFI), SCM will allow to fully characterize the wave polarization and estimate the direction of propagation of the wave energy. These measurements are crucial to understand the role of electromagnetic waves in the energy conversion processes, the plasma and energy transport, the acceleration and the heating of the plasma.
Particle-In-Cell simulations of an electron beam: stability and wave emissions
No full textInternational audienceDuring peaks of magnetospheric activity, energetic electrons trapped in the inner magnetosphere can precipitate in the lower ionosphere due to electromagnetic wave activity. Such waves can be generated naturally or artificially, for instance, through the emission of plasma beams. In this work, we study waves generated by electron beams emitted parallel to the magnetic field using fully kinetic Particle-In-Cell simulations. To this end, we use the heavily parallelized SMILEI code. To reduce the weight of the simulation, we take advantage of the rotational symmetry of the problem and use a cylindrical frame, which reduces the simulation to a 2D problem with cylindrical symmetry. We investigate the impact of the beam characteristics (such as beam density, frequency, length, etc.) on the wave generation, and the structural evolution of the beam as it exchanges energy with the electromagnetic fields and interacts with the background plasma
Euclid preparation. Cosmology Likelihood for Observables in Euclid (CLOE). 6: Impact of systematic uncertainties on the cosmological analysis
No full textInternational audienceExtracting cosmological information from the Euclid galaxy survey will require modelling numerous systematic effects during the inference process. This implies varying a large number of nuisance parameters, which have to be marginalised over before reporting the constraints on the cosmological parameters. This is a delicate process, especially with such a large parameter space, which could result in biased cosmological results. In this work, we study the impact of different choices for modelling systematic effects and prior distribution of nuisance parameters for the final Euclid Data Release, focusing on the 32pt analysis for photometric probes and the galaxy power spectrum multipoles for the spectroscopic probes. We explore the effect of intrinsic alignments, linear galaxy bias, magnification bias, multiplicative cosmic shear bias and shifts in the redshift distribution for the photometric probes, as well as the purity of the spectroscopic sample. We find that intrinsic alignment modelling has the most severe impact with a bias up to on the Hubble constant if neglected, followed by mis-modelling of the redshift evolution of galaxy bias, yielding up to on the parameter . Choosing a too optimistic prior for multiplicative bias can also result in biases of the order of on . We also find that the precision on the estimate of the purity of the spectroscopic sample will be an important driver for the constraining power of the galaxy clustering full-shape analysis. These results will help prioritise efforts to improve the modelling and calibration of systematic effects in Euclid
Euclid preparation. Cosmology Likelihood for Observables in Euclid (CLOE). 5. Extensions beyond the standard modelling of theoretical probes and systematic effects
No full textInternational audienceEuclid is expected to establish new state-of-the-art constraints on extensions beyond the standard LCDM cosmological model by measuring the positions and shapes of billions of galaxies. Specifically, its goal is to shed light on the nature of dark matter and dark energy. Achieving this requires developing and validating advanced statistical tools and theoretical prediction software capable of testing extensions of the LCDM model. In this work, we describe how the Euclid likelihood pipeline, Cosmology Likelihood for Observables in Euclid (CLOE), has been extended to accommodate alternative cosmological models and to refine the theoretical modelling of Euclid primary probes. In particular, we detail modifications made to CLOE to incorporate the magnification bias term into the spectroscopic two-point correlation function of galaxy clustering. Additionally, we explain the adaptations made to CLOE's implementation of Euclid primary photometric probes to account for massive neutrinos and modified gravity extensions. Finally, we present the validation of these CLOE modifications through dedicated forecasts on synthetic Euclid-like data by sampling the full posterior distribution and comparing with the results of previous literature. In conclusion, we have identified in this work several functionalities with regards to beyond-LCDM modelling that could be further improved within CLOE, and outline potential research directions to enhance pipeline efficiency and flexibility through novel inference and machine learning techniques
De la possibilité d'ignorer un bruit de calibration lors de la construction d'un estimateur du maximum de vraisemblance en radio-astronomie
No full textInternational audienceWe propose a method for quantifying the loss of precision in the estimation of parameters of interest when a calibration noise is neglected. The method is based on the use of the Cramér-Rao Bound (CRB) and the modified CRB, this latter being a lower bound on the covariance matrix of an estimator built with a misspecified model. The approach is illustrated on a simple theoretical case before being applied to the case of astrophysical data, where we estimate the kinetic temperature and the volume density of the interstellar medium. The accuracy loss, less than 13%, is negligeable given the complexity of the problem under consideration.Nous présentons une méthodologie permettant de quantifier la perte de précision sur l'estimation de paramètres d'intérêt lorsqu'un bruit de calibration est négligé. L'approche repose sur l'utilisation des bornes de Cramér-Rao (BCR) et BCR modifiée (BCRM), cette dernière étant une borne inférieure sur la matrice de covariance d'un estimateur construit avec un modèle mal spécifié. La méthode est illustrée sur un cas théorique simple avant d'être appliquée au cas de données astrophysiques, où on estime la température cinétique et la densité volumique du gaz interstellaire. La perte de précision mesurée, inférieure à 13%, est négligeable compte-tenu de la complexité du problème astrophysique considéré
VHE -ray observations of bright BL Lacs with the Large-Sized Telescope prototype (LST-1) of the CTAO
No full textInternational audienceCherenkov Telescope Array Observatory (CTAO) is the next-generation ground-based gamma-ray observatory operating in the energy range from 20 GeV up to 300 TeV, with two sites in La Palma (Spain) and Paranal (Chile). It will consist of telescopes of three sizes, covering different parts of the large energy range. We report on the performance of Large-Sized Telescope prototype (LST-1) in the detection and characterization of extragalactic gamma-ray sources, with a focus on the reconstructed gamma-ray spectra and variability of classical bright BL Lacertae objects, which were observed during the early commissioning phase of the instrument. LST-1 data from known bright gamma-ray blazars - Markarian 421, Markarian 501, 1ES 1959+650, 1ES 0647+250, and PG 1553+113 - were collected between July 10, 2020, and May 23, 2022, covering a zenith angle range of 4 deg to 57 deg. The reconstructed light curves were analyzed using a Bayesian block algorithm to distinguish the different activity phases of each blazar. Simultaneous Fermi-LAT data were utilized to reconstruct the broadband -ray spectra for the sources during each activity phase. High-level reconstructed data in a format compatible with gammapy are provided together with measured light curves and spectral energy distributions (SEDs) for several bright blazars and an interpretation of the observed variability in long and short timescales. Simulations of historical flares are generated to evaluate the sensitivity of LST-1. This work represents the first milestone in monitoring bright BL Lacertae objects with a CTAO telescope
Euclid Quick Data Release (Q1). An investigation of optically faint, red objects in the Euclid Deep Fields
No full textInternational audienceOur understanding of cosmic star-formation at used to largely rely on rest-frame UV observations. However, these observations overlook dusty and massive sources, resulting in an incomplete census of early star-forming galaxies. Recently, infrared data from Spitzer and the James Webb Space Telescope (JWST) have revealed a hidden population at 3-6 with extreme red colours. Taking advantage of the overlap between imaging in the Euclid Deep Fields (EDFs), covering 60 deg, and ancillary Spitzer observations, we identified 27000 extremely red objects with (dubbed HIEROs) down to a completeness magnitude limit of IRAC2 22.5 AB. After a visual inspection to discard artefacts and objects with troubling photometry, we ended up with a final sample of 3900 candidates. We retrieved the physical parameter estimates for these objects from the SED-fitting tool CIGALE. Our results confirm that HIERO galaxies may populate the high-mass end of the stellar mass function at , with some reaching extreme stellar masses () and exhibiting high dust attenuation (). However, we consider stellar mass estimates unreliable for , favouring a lower-z solution. The challenges faced by SED-fitting tools in characterising these objects highlight the need for further studies, incorporating shorter-wavelength and spectroscopic data. Euclid spectra will help resolve degeneracies and better constrain the physical properties of the brightest galaxies. Given the extreme nature of this population, characterising these sources is crucial for understanding galaxy evolution. This work demonstrates Euclid's potential to provide statistical samples of rare, massive, dust-obscured galaxies at , which will be prime targets for JWST, ALMA, and ELT
Tracing the galaxy-halo connection with galaxy clustering in COSMOS-Web from z = 0.1 to z ∼ 12
No full textInternational audienceWe explore the evolving relationship between galaxies and their dark matter halos from z ∼ 0.1 to z ∼ 12 using mass-limited angular clustering measurements in the 0.54 deg2 of the COSMOS-Web survey, the largest contiguous JWST extragalactic survey. This study provides the first measurements of the mass-limited two-point correlation function at z ≥ 10 and a consistent analysis spanning 13.4 Gyr of cosmic history, setting new benchmarks for future simulations and models. Using a halo occupation distribution (HOD) framework, we derived characteristic halo masses and the stellar-to-halo mass ratio (SHMR) across redshifts and stellar mass bins. Our results first indicate that HOD models fit data at z ≥ 2.5 best when incorporating a nonlinear scale-dependent halo bias, boosting clustering at nonlinear scales (r = 10 − 100 kpc). We find that galaxies at z ≥ 10.5 with log(M⋆/M⊙)≥8.85 are predominantly central galaxies in halos with Mh ∼ 1010.5 M⊙, achieving a star formation efficiency (SFE) of εSF = M⋆/(fbMh) up to 1 dex higher than at z ≤ 1. The high galaxy bias at z ≥ 8 suggests that these galaxies reside in massive halos with an intrinsic high SFE, challenging stochastic SHMR scenarios. Our SHMR evolves significantly with redshift, starting very high at z ≥ 10.5, decreasing until z ∼ 2 − 3, then increasing again until the present. Current hydrodynamical simulations fail to reproduce both massive high-z galaxies and this evolution, while semi-empirical models linking SFE to halo mass, accretion rates, and redshift align with our findings. We propose that early galaxies (z > 8) experience bursty star formation without significant feedback altering their growth, driving the rapid growth of massive galaxies observed by JWST. Over time, the increasing feedback efficiency and the exponential halo growth end up suppressing star formation. At z ∼ 2 − 3 and later, the halo growth slows down, while star formation continues, supported by gas reservoirs in halos
The H.E.S.S. Gravitational Wave and Gamma-Ray Burst Follow-Up Programs
No full textInternational audienceMulti-wavelength and multi-messenger astrophysics have experienced rapid growth over the past decade, seeking a complete picture of different cosmic phenomena. Transient sources, in particular, benefit from the input of multi-messenger observations, offering complementary perspectives on the same event while maximizing the detection probability of a rapidly fading signal.In this context, Gravitational Wave (GW) detections serve as perfect triggers for potential counterpart detections. Notably, a GW alert could be associated with a Gamma-Ray Burst (GRB), jetted cataclysmic events produced either by the collision of a binary neutron star system or a core-collapse supernova. These sources also radiate across the electromagnetic spectrum, allowing detection by X- and gamma-ray instruments aboard various satellites and thus enabling multi-wavelength triggering opportunities. The strong interest in minimizing reaction time to capture the full-time evolution of the emission, together with the often challenging localization uncertainties of the alerts, underscores the need for rapid and well-coordinated follow-up programs such as the one developed by the H.E.S.S. Collaboration.This contribution will give an overview of the transient follow-up strategy carried out by the H.E.S.S. Collaboration, from the external alert trigger and the automatic reaction of the observatory to the various analysis steps of the obtained observations. To illustrate this comprehensive strategy, we will show two examples of follow-up observations of both GRBs and GWs, highlighting key results and challenges in the search for an associated high-energy gamma-ray emission