Upper Limits on the Isotropic Gravitational-Wave Background from the first part of LIGO, Virgo, and KAGRA's fourth Observing Run

International audienceWe present results from the search for an isotropic gravitational-wave background using Advanced LIGO and Advanced Virgo data from O1 through O4a, the first part of the fourth observing run. This background is the accumulated signal from unresolved sources throughout cosmic history and encodes information about the merger history of compact binaries throughout the Universe, as well as exotic physics and potentially primordial processes from the early cosmos. Our cross-correlation analysis reveals no statistically significant background signal, enabling us to constrain several theoretical scenarios. For compact binary coalescences which approximately follow a 2/3 power-law spectrum, we constrain the fractional energy density to $Ω_{\rm GW}(25{\rm Hz})\leq 2.0\times 10^{-9}$ (95% cred.), a factor of 1.7 improvement over previous results. Scale-invariant backgrounds are constrained to $Ω_{\rm GW}(25{\rm Hz})\leq 2.8\times 10^{-9}$, representing a 2.1x sensitivity gain. We also place new limits on gravity theories predicting non-standard polarization modes and confirm that terrestrial magnetic noise sources remain below detection threshold. Combining these spectral limits with population models for GWTC-4, the latest gravitational-wave event catalog, we find our constraints remain above predicted merger backgrounds but are approaching detectability. The joint analysis combining the background limits shown here with the GWTC-4 catalog enables improved inference of the binary black hole merger rate evolution across cosmic time. Employing GWTC-4 inference results and standard modeling choices, we estimate that the total background arising from compact binary coalescences is $Ω_{\rm CBC}(25{\rm Hz})={0.9^{+1.1}_{-0.5}\times 10^{-9}}$ at 90% confidence, where the largest contribution is due to binary black holes only, $Ω_{\rm BBH}(25{\rm Hz})=0.8^{+1.1}_{-0.5}\times 10^{-9}$

A Concise Presentation of the Life of Padmasambhava

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Littératures comparées: [résumé des cours et travaux : 2021-2022]

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Impact of active galactic nuclei and nuclear star formation on the ISM turbulence of galaxies: Insights from JWST/MIRI spectroscopy

International audienceActive galactic nuclei (AGNs), star formation (SF), and galaxy interactions can drive turbulence in the gas of the interstellar medium (ISM), which, in turn, plays a role in SF taking place within galaxies. The impact on molecular gas is of particular importance, as it serves as the primary fuel for SF. Our goal is to investigate the origin of turbulence and the emission of molecular gas, as well as low-and-intermediate-ionisation gas, in the inner few kpc of both AGN hosts and star-forming galaxies (SFGs). We used archival JWST MIRI/MRS observations of a sample consisting of 54 galaxies at z < 0.1. We present flux measurements for the H2 S(5)λ6.9091 μm, [ArII]λ6.9853 μm, [FeII]λ5.3403 μm, and [ArIII]λ8.9914 μm emission lines along with velocity dispersion estimated by the W80 parameter. For galaxies with coronal line emission, we included measurements of the [MgV]λ5.6098 μm line. We compared the line ratios to photoionisation and shock models to explore the origin of the gas emission. AGNs exhibit broader emission lines than SFGs, with the largest velocity dispersions observed in radio-strong (RS) AGNs. The H2 gas is less turbulent compared to ionised gas, while coronal gas presents higher velocity dispersions. The W80 values for the ionised gas show a decrease when going from the nucleus out to radii of approximately 0.5–1 kpc, followed by an outward increase up to 2–3 kpc. In contrast, the H2 line widths generally display increasing profiles with distance from the center. Correlations between the W80 parameter and line ratios such as H2S(5)/[Ar II] and [Fe II]/[Ar II] indicate that the most turbulent gas is associated with shocks, enhancing H2 and [Fe II] emissions. Based on the observed line ratios and velocity dispersions, the [FeII] emission is consistent with predictions of fast shock models, while the H2 emission is likely associated with molecules formed in the post-shock region. We speculate that these shocked gas regions are produced by AGN outflows and jet-cloud interactions in AGN-dominated sources; whereas in SFGs, they might be created through stellar winds and mergers. This shock-induced gas heating may be an important mechanism of AGN (or stellar) feedback, preventing the gas from cooling and forming new stars.Key words: galaxies: active / galaxies: evolution / galaxies: ISM / galaxies: kinematics and dynamic

Une écriture “excentrique” : l’exemple de Furukawa Hideo: An “Eccentric” Form of Writing: The Case of Furukawa Hideo

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Faire taire l’intertextualité ? La réception de l’œuvre d’Agapios Landos dans la controverse eucharistique autour de la Perpétuité de la foi (1669)

International audienceThis article examines the reception of the Salut des pécheurs by Agapios Landos in the first volume of the Perpétuité de la foi. Having identified the collection of works consulted by French theologians, we analyse the construction of the image of Agapios as an archetype of an Orthodox Athonite, affirming faith in the real presence of Christ in the Eucharist, and the need for “good dispositions” in order to receive communion worthily. Nevertheless, Agapios’s work is strongly inspired by Catholic sources, and this interconfessional substratum is deliberately hidden by the author himself and by French theologians, while the overconfessionalisation of the image of Agapios, by both these parties, relates in each case to the intraconfessional issues specific to Greek Orthodoxy and French Catholicism.Nous interrogeons la réception du Salut des pécheurs d’Agapios Landos dans le premier tome de la Perpétuité de la foi. Ayant identifié la collection des ouvrages consultée par les Messieurs de Port-Royal, nous y analysons la construction de l’image d’Agapios devenant un archétype d’athonite orthodoxe témoin de la foi dans la présence réelle et dans la nécessité des « bonnes dispositions » pour communier dignement. En revanche, l’ouvrage d’Agapios est fortement inspiré par des sources catholiques, et ce substrat interconfessionnel est caché délibérément par l’auteur lui-même et par les théologiens français, tandis que la surconfessionnalisation de l’image d’Agapios se fait dans les deux cas par rapport aux enjeux intraconfessionnels propres à l’orthodoxie grecque et au catholicisme français

Non-resonant plasmon energy transfer processes for catalysis

International audienceHow can energy transfer catalysis move beyond fragile molecular light absorbers toward more robust and tunable systems? Here we show that tiny gold nanostructures can act as universal energy donors to activate otherwise inactive gold-based catalysts using light. By introducing a molecular mediator, we demonstrate that the localized energy within the nanoparticles can be passed along through a twostep mechanism, ultimately creating a reactive excited state in the gold complex, even when the light does not directly match its energy levels. Spectroscopic measurements confirm the formation and lifetime of this state and provide clear evidence of successful energy transfer. These results establish how plasmonic materials can drive catalytic reactions through controlled energy flow, opening new opportunities for designing durable and versatile systems for light-driven chemistry

An ancient DNA perspective on the Russian conquest of Yakutia

International audienceYakut communities from northeastern Siberia inhabit some of the coldest environments on Earth, preserving an extraordinary archaeological record. Their history was profoundly reshaped by the Russian conquest, which introduced cereals, pathogens and Christianity beginning in 1632 (refs. 1,2,3,4,5). However, the biological impact of these transformations remains unknown. Here we generated extensive ancient DNA data to elucidate contemporary changes in Yakut genomic diversity and oral microbiomes. We found Yakut origins tracing back to local populations that admixed with Trans-Baikal groups migrating as the Great Mongol Empire spread. Despite the Russian conquest, the Yakut gene pool and oral microbiomes appeared largely stable, although smallpox strains distinct from those documented in Europe by approximately 1650 circulated. Marital practices generally maintained low consanguinity, with the exception of one female bearing the latest markers of traditional shamanism, who was the daughter of second-degree relatives

Pascal intempestif [actes du colloque du Collège de France d'octobre 2023]

International audienceSteeped in the knowledge of his time and characterised by a provocative disdain for science and apparent anti-humanism, Pascal's work is divisive and problematic. Combining critical approaches, this volume examines his incongruity with his contemporaries and often with our own modernity.Pénétrée des savoirs de son temps, provocante par sa déconsidération de la science et un apparent anti-humanisme, l’œuvre de Pascal est clivante et problématique. Mêlant les approches critiques, le volume envisage cette intempestivité à l’égard de ses contemporains et, souvent, de notre modernité