HAL-INSU
Not a member yet
203706 research outputs found
Sort by
Whole-disk sampling of molecular clouds in M83
No full textAccepted for publication in ApJInternational audienceWe present a catalog of clouds identified from the CO (1--0) data of M83, which was observed using Atacama Large Millimeter/submillimeter Array (ALMA) with a spatial resolution of 46 pc and a mass sensitivity of 10 (3 ). The almost full-disk coverage and high sensitivity of the data allowed us to sample 5724 molecular clouds with a median mass of , which is comparable to the most frequently sampled mass of Giant Molecular Clouds by surveys in the Milky Way. About 60 percent of the total CO luminosity in M83's disk arises from clouds more massive than 10 . Such massive clouds comprise 16 percent of the total clouds in number and tend to concentrate toward the arm, bar, and center, while smaller clouds are more prevalent in inter-arm regions. Most >10^6 clouds have peak brightness temperatures above 2 K with the current resolution. Comparing the observed cloud properties with the scaling relations determined by Solomon et al. 1987 (S87), >2 K clouds follow the relations, but <2 K clouds, which are dominant in number, deviate significantly. Without considering the effect of beam dilution, the deviations would suggest modestly high virial parameters and low surface mass densities for the entire cloud samples, which are similar to values found for the Milky Way clouds by Rice et al. (2016) and Miville-Desch{\^e}nes et al. (2017). However, once beam dilution is taken into account, the observed and for a majority of the clouds (mostly <2 K) can be potentially explained with intrinsic of 100 and of 1, which are similar to the clouds of S87
Buchdahl bound, photon ring, ISCO and radial acceleration in Einstein-æther theory
No full textInternational audienceSpherically symmetric Einstein-æther (EÆ) theory with a Maxwell-like kinetic term is revisited. We consider a general choice of the metric and the æther field, finding that:~(i) there is a gauge freedom allowing one always to use a diagonal metric; and~(ii) the nature of the Maxwell equation forces the æther field to be time-like in the coordinate basis. We derive the vacuum solution and confirm that the innermost stable circular orbit (ISCO) and photon ring are enlarged relative to general relativity (GR). Buchdahl's theorem in EÆ theory is derived. For a uniform physical density, we find that the upper bound on compactness is always lower than in GR. Additionally, we observe that the Newtonian and EÆ radial acceleration relations run parallel in the low pressure limit. Our analysis of EÆ theory may offer novel insights into its interesting phenomenological generalization: Æther--scalar--tensor theory (ÆST)
Reconstructing Galaxy Cluster Mass Maps using Score-based Generative Modeling
No full textInternational audienceWe present a novel approach to reconstruct gas and dark matter projected density maps of galaxy clusters using score-based generative modeling. Our diffusion model takes in mock SZ and X-ray images as conditional observations, and generates realizations of corresponding gas and dark matter maps by sampling from a learned data posterior. We train and validate the performance of our model by using mock data from a hydrodynamical cosmological simulation. The model accurately reconstructs both the mean and spread of the radial density profiles in the spatial domain to within 5%, indicating that the model is able to distinguish between clusters of different sizes. In the spectral domain, the model achieves close-to-unity values for the bias and cross-correlation coefficients, indicating that the model can accurately probe cluster structures on both large and small scales. Our experiments demonstrate the ability of score models to learn a strong, nonlinear, and unbiased mapping between input observables and fundamental density distributions of galaxy clusters. These diffusion models can be further fine-tuned and generalized to not only take in additional observables as inputs, but also real observations and predict unknown density distributions of galaxy clusters
The eventful life of a luminous galaxy at z = 14: metal enrichment, feedback, and low gas fraction?
No full textInternational audienceJADES-GS-z14-0 is the most distant spectroscopically confirmed galaxy so far, at z>14. With a UV magnitude of -20.81, it is one of the most luminous galaxies at cosmic dawn and its half-light radius of 260 pc means that stars dominate the observed UV emission. We report the ALMA detection of [OIII]88m line emission with a significance of 6.67 and at a frequency of 223.524 GHz, corresponding to a redshift of , which is consistent with the candidate CIII] line detected in the NIRSpec spectrum. At this spectroscopic redshift, the Lyman break identified with NIRSpec requires a damped Lyman- absorber with a column density of . The total [OIII]88m luminosity (log() is fully consistent with the local relation. Based on the , we infer a gas-phase metallicity >0.1~{\rm Z_{\rm \odot}}, which is somewhat unexpected given the weakness of the UV emission lines. Using prospector SED modeling and combining the ALMA data with JWST observations, we find and an escape fraction of ionizing photons of 20%, which is necessary to explain the UV spectrum. We measure an [O III]5007\r{A}/[O III]88m line flux ratio between 1 and 10, resulting in an upper limit to the electron density of roughly 300 cm, which is lower than those measured in other high- luminous galaxies. The [OIII]88m emission line is spectrally resolved, with a FWHM of 100 km/s, resulting in a dynamical mass of (M) = 9.0. This value is comparable to the stellar mass derived from the SED fitting, which implies a very low gas fraction. Past radiation-driven outflows may have cleared the galaxy from the gas, reducing the gas fraction and thus increasing the escape fraction of ionizing photons
Implicit EXP-RBF techniques for modeling unsaturated flow through soils with water uptake by plant roots
No full textInternational audienceRoot water uptake Soil-water-plant interactions Meshfree methods Localized radial basis function EXP-RBF BDF2Modeling unsaturated flow through soils with water uptake by plant root has many applications in agriculture and water resources management. In this study, our aim is to develop efficient numerical techniques for solving the Richards equation with a sink term due to plant root water uptake. The Feddes model is used for water absorption by plant roots, and the van-Genuchten model is employed for capillary pressure. We introduce a numerical approach that combines the localized exponential radial basis function (EXP-RBF) method for space and the second-order backward differentiation formula (BDF2) for temporal discretization. The localized RBF methods eliminate the need for mesh generation and avoid ill-conditioning problems. This approach yields a sparse matrix for the global system, optimizing memory usage and computational time. The proposed implicit EXP-RBF techniques have advantages in terms of accuracy and computational efficiency thanks to the use of BDF2 and the localized RBF method. Modified Picards iteration method for the mixed form of the Richards equation is employed to linearize the system. Various numerical experiments are conducted to validate the proposed numerical model of infiltration with plant root water absorption. The obtained results conclusively demonstrate the effectiveness of the proposed numerical model in accurately predicting soil moisture dynamics under water uptake by plant roots. The proposed numerical techniques can be incorporated in the numerical models where unsaturated flows and water uptake by plant roots are involved such as in hydrology, agriculture, and water management.</div
Silver-Tungsten induced codeposition: Influence of pH and carboxylic acid form in a DMH-based electrolyte
No full textInternational audienceSilver-tungsten coatings were successfully electrodeposited on platinum and copper substrates from a non-toxic 5.5-dimethylhydantoin electrolyte at low pH and two different carboxylic acid forms: citrate or tartrate. Tungsten contents remain at low levels compared to former works, but close to the values considered as optimal for functional properties without having to recourse to controversial substances such as thiourea. Electrochemical studies by linear sweep voltammetry allow to distinguish two typical behaviors and give interesting insight into the induced codeposition mechanism. Silver-tungsten codeposition only occurred at pH 2.0 and 3.5 using citrates and at pH 2.0 using tartrates, corresponding to the forms H3Cit, H2Cit-2, and H2Tar, respectively. No silver-tungsten reduction was possible with less than two protonated carboxyl groups on either tartrate or citrate ions. Separate silver and tungsten lattice are both present in the resulting alloy. Grain and crystallite sizes were observed by SEM. XPS investigations show that for our low W content alloys, silver is found to be metallic whereas tungsten is present in oxide form. The carbon peaks and also gaps between peaks when N is absent indicate that citrates are present in the coating, unlike DMH
Nickel Ecotoxicity to Raphidocelis subcapitata in Standard ISO Medium vs. Ultramafic Waters
No full textInternational audiencePristine ultramafic waters (PUW) usually have Ni concentrations in excess of environmental quality standard (EQS) even in the absence of anthropogenic influence. However, PUW are also rich in colloidal carrier phases (e.g., Fe-hydroxides and natural organic matter) that can mitigate Ni ecotoxicity by reducing its bioavailability.PUW were collected from the Pluhuv Bor creek (PLB, a small catchment in the western Czech Republic) during snowmelt and tested for their possible ecotoxicity to a model alga in relation to their high Ni content (> 100 µg/L). Ecotoxicity testing was carried using the freshwater alga Raphidocelis subcapitata and following the ISO norm 8692. Preliminary work established a Ni 72h-EC50 of around 30 µg/L for algal growth in ISO medium; a value 3- to 5-fold lower than concentrations measured in PLB waters (114–164 µg/L filterable Ni; 0.22 µm). However, PLB waters did not reduce algal biomass compared with control exposures. Characterization of Ni speciation using filtration/ultrafiltration showed that 70–80% of filterable Ni was associated with colloids, resulting in ultrafilterable Ni concentrations (< 3 kDa) of 30–37 µg/L. Bioavailable Ni concentrations, estimated with a user-friendly BLM tool, were 12–17 and 8–13 µg/L in filtered and ultrafiltered waters, respectively; these values being close to the Ni 72h EC10 determined in standard ISO medium. Testing of PLB waters spiked with NiCl2 (14–250 µg/L as Ni) did not result in appreciable ecotoxic effect, either. Modelled bioavailable Ni-concentrations in PLB samples spiked with 250 µg/L of soluble Ni were around 40 µg/L, i.e., above the EC50 value determined in ISO medium. Further research appears necessary to understand how the interplay between speciation and bioavailability affects the ecotoxic potential of Ni in the complex matrix of PUW
PHAST
No full textInternational audienceAbstract The Panchromatic Hubble Andromeda Southern Treasury (PHAST) is a large 195-orbit Hubble Space Telescope program imaging ∼0.45 deg 2 of the southern half of M31's star-forming disk at optical and near-ultraviolet (NUV) wavelengths. The PHAST survey area extends the northern coverage of the Panchromatic Hubble Andromeda Treasury (PHAT) down to the southern half of M31, covering out to a radius of ∼13 kpc along the southern major axis and in total ∼two-thirds of M31's star-forming disk. This new legacy imaging yields stellar photometry of over 90 million resolved stars using the Advanced Camera for Surveys in the optical (F475W and F814W), and the Wide Field Camera 3 (WFC3) in the NUV (F275W and F336W). The photometry is derived using all overlapping exposures across all bands, and achieves a 50% completeness-limited depth of F475W ∼ 27.7 in the lowest surface density regions of the outer disk and F475W ∼ 26.0 in the most crowded, high surface brightness regions near M31's bulge. We provide extensive analysis of the data quality, including artificial star tests to quantify completeness, photometric uncertainties, and flux biases, all of which vary due to the background source density and the number of overlapping exposures. We also present seamless population maps of the entire M31 disk, which show relatively well-mixed distributions for stellar populations older than 1–2 Gyr, and highly structured distributions for younger populations. The combined PHAST + PHAT photometry catalog of ∼0.2 billion stars is the largest ever produced for equidistant sources and is available for public download by the community
Machine learning based Photometric Redshifts for Galaxies in the North Ecliptic Pole Wide field: catalogs of spectroscopic and photometric redshifts
No full textInternational audienceWe perform an MMT/Hectospec redshift survey of the North Ecliptic Pole Wide (NEPW) field covering 5.4 square degrees, and use it to estimate the photometric redshifts for the sources without spectroscopic redshifts. By combining 2572 newly measured redshifts from our survey with existing data from the literature, we create a large sample of 4421 galaxies with spectroscopic redshifts in the NEPW field. Using this sample, we estimate photometric redshifts of 77755 sources in the band-merged catalog of the NEPW field with a random forest model. The estimated photometric redshifts are generally consistent with the spectroscopic redshifts, with a dispersion of 0.028, an outlier fraction of 7.3%, and a bias of -0.01. We find that the standard deviation of the prediction from each decision tree in the random forest model can be used to infer the fraction of catastrophic outliers and the measurement uncertainties. We test various combinations of input observables, including colors and magnitude uncertainties, and find that the details of these various combinations do not change the prediction accuracy much. As a result, we provide a catalog of 77755 sources in the NEPW field, which includes both spectroscopic and photometric redshifts up to z~2. This dataset has significant legacy value for studies in the NEPW region, especially with upcoming space missions such as JWST, Euclid, and SPHEREx
Training deep learning models with a multi-station approach and static aquifer attributes for groundwater level simulation: what is the best way to leverage regionalised information?
No full text(IF 5.7;Q2)International audienceIn this study, we use deep learning models with advanced variants of recurrent neural networks, specifically long short-term memory (LSTM), gated recurrent unit (GRU), and bidirectional LSTM (BiLSTM), to simulate large-scale groundwater level (GWL) fluctuations in northern France. We develop multi-station collective training for GWL simulations, using dynamic variables (i.e. climatic) and static basin characteristics. This large-scale approach can incorporate dynamic and static features to cover more reservoir heterogeneities in the study area. Further, we investigated the performance of relevant feature extraction techniques such as clustering and wavelet transform decomposition to simplify network learning using regionalised information. Several modelling performance tests were conducted. Models specifically trained on different types of GWL, clustered based on the spectral properties, performed significantly better than models trained on the whole dataset. Clustering-based modelling reduces complexity in the training data and targets relevant information more efficiently. Applying multi-station models without prior clustering can lead the models to preferentially learn the dominant behaviour, ignoring unique local variations. In this respect, wavelet pre-processing was found to partially compensate for clustering, bringing out common temporal and spectral characteristics shared by all available GWL time series even when these characteristics are "hidden" (e.g. if their amplitude is too small). When employed along with prior clustering, using wavelet decomposition as a pre-processing tech-nique significantly improves model performances, particularly for GWLs dominated by low-frequency interannual to decadal variations. This study advances our understanding of GWL simulation using deep learning, highlighting the importance of different model training approaches, the potential of wavelet pre-processing, and the value of incorporating static attributes