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203706 research outputs found
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Characterizing the outer disk of extended-UV galaxies in the optical domain with deep surveys
No full textInternational audienceAims. Extended-UV (XUV) galaxies are galaxies that present an extended outer ultraviolet disk. Although some giant low surface brightness (GLSB) galaxies are also XUV, their relation has been seldom studied. This work aims to determine whether a sample of nine XUV galaxies can be classified as GLSB galaxies, by analyzing their photometric properties in deep optical images. Methods. The method presented here used optical data from the Dark Energy Survey to construct surface brightness profiles for each galaxy. We defined a characteristic UV radius to examine the XUV disks. We fitted the surface brightness profiles using simple exponential functions, and compared the extracted parameters with the literature to identify possible GLSB galaxies. We also examined other diagnostics, including color profiles.Results. The analysis of the optical surface brightness profiles of XUV galaxies reveals that they can be classified into three different families. One third meet the GLSB criteria in terms of diffuseness, another third are regular, and the remaining have a stronger decline in the outer disk than in the inner disk, which is opposite to the characteristics of GLSB galaxies. The color profile allowed us to distinguish one galaxy, NGC1140, and speculate that it is the result of a rare dwarf-dwarf merger
Response of Early Winter Precipitation and Storm Activity in the North Atlantic–European–Mediterranean Region to Indian Ocean SST Variability
No full textInternational audienceAbstract We investigate the response of winter precipitation and storm activity in the North Atlantic–European–Mediterranean region (NAEM) to the Indian Ocean Dipole (IOD) from 1979 to 2024. We observe a positive NAO‐like pattern over NAEM, which appears in December and shifts eastward through February. IOD further modulates precipitation by inducing changes in total precipitation, event frequency, and wet spell duration. The strength of the observed teleconnection is primarily significant in December. Additionally, we observe a reduction in cyclone activity in December over the East Atlantic and Western Mediterranean. These changes in cyclone track density are primarily driven by variations in the Eady Growth Rate, which are linked to enhanced vertical wind shear associated with a strengthened meridional temperature gradient over the NAEM. The results underscore a significant remote impact of the IOD on early winter hydro‐climate variability over the NAEM region, offering a potential value for improving sub‐seasonal to seasonal prediction
The subtleties of three-dimensional radiative effects in contrails and cirrus clouds
No full textInternational audienceAbstract. The radiative effect of cirrus, contrails, and contrail cirrus affects the energy budget of the Earth and climate change. Those clouds, and especially contrails, are heterogeneous and their holes and sides exert three-dimensional radiative effects. This study uses the htrdr Monte Carlo radiative transfer code to investigate the sensitivity of the cloud radiative effect (CRE) to the geometrical dimensions and optical depth of optically thin ice clouds (cloud optical depth <4), with particular emphasis on three-dimensional radiative effects. When the Sun is at zenith, an increase in cloud optical depth causes a linear increase in shortwave (SW) CRE but a saturation of longwave (LW) CRE, causing the net CRE to change sign from positive to negative. The optical depth at which this change in sign occurs depends on the cloud geometry. 3D effects make the one-dimensional SW and LW CREs more positive for the Sun at zenith, reaching the same order of magnitude as the 1D CRE itself for clouds with high aspect ratios. The angular dependence of ice crystal scattering strongly increases shortwave CRE when solar zenith angle increases. 3D effects change sign from positive at zenith to negative at large zenith angles as the Sun's rays interact more with the cloud sides. Integrating instantaneous CRE and 3D effects over selected days of the year indicates compensation of SW with LW 3D effects for some cloud orientations, but 3D effects remain important in some cases. These results suggest that the 3D structure of cirrus and contrails needs to be considered to finely quantify their CRE and radiative forcing
New strategies and new challenges for pesticide studies: how to combine the preservation of our environment and sustainable agriculture?
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Forming the local starburst galaxy Haro 11 through hydrodynamical merger simulations
No full textInternational audienceHaro 11 is a metal-poor, starburst galaxy believed to be the result of an ongoing merger, which is shaping the properties of the galaxy. In this study, we carry out a large suite of numerical simulations of a merger between two disc galaxies, to study possible origins of Haro 11 and understand under which conditions various features of the galaxy are formed. By varying galaxy parameters describing the orbital configurations, masses, and their inclination, we perform a total of ∼500 simulations. We demonstrate that a two-disc galaxy merger reproduces key, observed features of Haro 11, including its morphology, gas kinematics, star formation history, and stellar population ages and masses. In particular, we present a fiducial Haro 11 model that produces the single observed tidal tail, three stellar knots, and inner gas morphology and kinematics. The resulting orbit and galactic morphology are robust against small variations of the initial parameters. By performing mock observations, we compare with the results of observational data and discuss possible origins for various features. Furthermore, we present newly gathered observational data that confirms the presence of a stellar tidal tail with similar length and morphology as our simulations.</div
Optimizing the total oxidizable precursor (TOP) assay: enhanced PFAS quantification and analytical gap bridging in complex environmental matrices
No full textInternational audienceThe Total Oxidizable Precursor (TOP) assay was optimized to overcome the limitations of targeted analyses in detecting diverse PFAS compounds. This study evaluated key factors influencing the assay’s effectiveness, including temperature, sorption, oxidation, and reagent-to-organic compound ratios, using both spiked solutions and real environmental matrices. The efficiency of solid-phase extraction (SPE) was assessed before and after the assay, revealing that post-oxidation SPE improved sensitivity, particularly at low PFAS concentrations. The modified TOP Assay quantified 56 PFAS and their oxidizable precursors, resulting in up to a 1000% increase in perfluoroalkyl carboxylic acids (PFCA), indicating the presence of unidentified compounds. PFAS precursors oxidation ranged from 78 to 100% in liquid samples and 64 to 100% in solid samples (wastewater, sewage sludge, compost, struvite), confirming the assay’s efficacy under optimized conditions (K₂S₂O₈: 240 mM; NaOH: 600 mM; 2.5 mL reaction volume). Optimal conditions were determined based on PFCA formation, precursor transformation rates, and inter-test consistency. This adaptable and versatile protocol enhances PFAS detection across a variety of environmental matrices. Future applications to solid samples could further improve estimates of PFAS contamination in the environmen
Linking Fe-Ca metasomatism and hydrothermal sulfide mineralization in mantle rocks: insights from geochemistry and thermodynamic modeling
No full textInternational audienceUltramafic-hosted seafloor massive sulfide deposits have been reported in present-day oceanic settings over the past thirty years. These deposits and their fossil on-land analogs represent potential important resources for Cu, Co, Ni, Zn. However, developing comprehensive genetic models for deep-seatedhydrothermal processes is hindered by limited seafloor observations and reliance on large-scale geophysical studies. To overcome this issue, one can examine fossil systems, where hydrothermal plumbing architecture may be preserved. The Platta nappe (Swiss Alps) preserves a Jurassic hydrothermal system (the Marmorera-Cotschen Hydrothermal System; MCHS), where Cu-Fe-Co-Zn-Ni mineralization is associated with coeval Fe-Ca silicates (ilvaite, hydro-garnet, and diopside). The MCHS is hosted in serpentinites, which have been exhumed along a Jurassic paleo-detachment —a fossil analog ofa large-scale exhumation fault that forms oceanic core complexes at slow-spreading ridges— juxtaposing basalts onto serpentinites. The serpentinized footwall has numerous mafic intrusions, and the mafic-ultramafic rock contacts served as pathways for ore-forming fluids. Petrographic analyses and thermodynamic modeling indicate that Fe-Ca metasomatism occurred between 300‒360°C and at relatively low fO2 (from Magnetite-Native Fe to Fayalite-Magnetite-Quartz buffers), likely coeval with early-stage serpentinization. The composition of Fe-Ca silicates (Co, Ni, and REE contents, measured by in situ LA-ICP-MS) points to heterogeneous geochemical reservoirs involved during fluid-rock interaction. The geochemical compositions of Fe-Ca silicates in barren assemblages indicate an ultramafic-dominated system, while Fe-Ca silicates in mineralized assemblages point to an open-system, involving fluids derived from both mafic and ultramafic rocks. Mineralogical and geochemical signatures of Fe-Ca silicates in the MCHS do not support genetic relationships with common rodingitization. Our results suggest that Fe-Ca metasomatism may be a widespread deep-seated alteration along mafic-ultramafic rock contacts or in mantle rocks modified through melt-rock interaction accompanying mantle exhumation. We acknowledge JdC Fellowship (FJC2021-047190-I), funded by MCIN/AEI/10.13039/501100011033 with EU Next Generation Funds and funding from project PID2022-136471NB-C21 “The role of ultramafic rocks and related rocks in the sulfur and water cycles and their implications for the redox state of subduction zones (RUSTED)”, funded byMCIN/AEI/10.13039/501100011033 and by the ESF+
Western Indian subantarctic phytoplankton blooms fertilized by iron-enriched Agulhas water
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Changes, interactions and drivers of soil chemical, physical and biological properties after repeated application of organic waste products in two contrasted long-term field experiments in France
No full textInternational audienceRecycling organic waste products (OWP) is known to influence soil physical, chemical, and biological properties, yet few studies have compared the long-term effects of different OWP type across multiple sites. This study examined the impacts of repeated OWP application on soil properties in two French long-term field experiments: QualiAgro and PROspective (20 and 18 years, respectively). The OWP included dehydrated urban sewage sludge (SLU), green waste and SLU compost (GWS), biowaste compost from source-separated municipal organic waste co-composted with green waste (BIO), municipal solid waste compost (MSW), farmyard manure from a dairy cow farm (FYM), and composted FYM from open-air composting on a concrete platform (FYMC). The application of OWP led to increased soil nutrient levels and trace element availability, and stimulated microbial biomass and enzyme activities, while the response of nematode varied depending on site and OWP type. Biological properties were less affected than physico-chemical properties, though the OWP application enhanced soil microbial biomass and specific enzyme activities. The impact on soil nematode communities varied depending on OWP type and site. Strong correlations were observed among soil property changes, with exogenous carbon and nutrient inputs from OWP identified as key drivers. Larger changes were noted in QualiAgro, where OWP application rates were higher and initial soil quality lower. These findings highlight that OWP applications, depending on their type, rate, and initial soil conditions, can significantly alter soil properties
Locking noise in laser frequency stabilization to an optical fiber delay line
No full textInternational audienceWe investigate the noise due to the locking process in frequency stabilization of a laser onto an optical fiber delay line with the Pound-Drever-Hall method. Preliminary measurements revealed a white frequency noise floor that limited the locking performance. We conducted a combined experimental and theoretical analysis to identify the source of this limitation, focusing on the role of frequency discriminator nonlinearity. By increasing the locking bandwidth, we demonstrate a reduction in this white noise to a level where this nonlinearity is no longer a limiting factor