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Molecular gas stratification and disturbed kinematics in the Seyfert galaxy MCG-05-23-16 revealed by JWST and ALMA
No full textInternational audienceUnderstanding the processes that drive the morphology and kinematics of molecular gas in galaxies is crucial for comprehending star formation and, ultimately, galaxy evolution. Using data from the Galactic Activity, Torus and Outflow Survey (GATOS) obtained with the James Webb Space Telescope (JWST) and the archival data from the Atacama Large Millimeter/submillimeter Array (ALMA), we study the behavior of the warm molecular gas at temperatures of hundreds of Kelvin and the cold molecular gas at tens of Kelvin in the galaxy MCG−05−23−16, which hosts an active galactic nucleus (AGN). Hubble Space Telescope (HST) images of this spheroidal galaxy, classified in the optical as S0, show a dust lane resembling a nuclear spiral and a surrounding ring. These features are also detected in CO(2−1) and H 2 , and their morphologies and kinematics are consistent with rotation plus local inward gas motions along the kinematic minor axis in the presence of a nuclear bar. The H 2 transitions 0-0 S(3), 0-0 S(4), and 0-0 S(5), which trace warmer and more excited gas, show more disrupted kinematics than 0-0 S(1) and 0-0 S(2), including clumps of high velocity dispersion (of up to ∼160 km s −1 ), in regions devoid of CO(2−1). The kinematics of one of these clumps, located ∼350 pc westward of the nucleus, are consistent with outflowing gas, possibly driven by localized star formation traced by polycyclic aromatic hydrocarbon emission at 11.3 μm. Overall, we observe a stratification of the molecular gas, with the colder gas located in the nuclear spiral, ring, and connecting arms, and most of the warmer gas with a higher velocity dispersion filling the inter-arm space. The compact jet, approximately 200 pc in size, detected with Very Large Array (VLA) observations, does not appear to significantly affect the distribution and kinematics of the molecular gas, possibly due to its limited intersection with the molecular gas disk
Episode 1: Ayah & the plasma-semiconductor frontier: Journey into the PhD founded by Amélie Elouin (Laboratory of Optics and Biosciences)
No full textIn this episode Xue receives Ayah and she will tel us about her PhD-thesis: the plasma-semiconductor frontier. Her research focuses on surface semiconducting barrier discharges, a type of plasma that propagates on a silicon surface. She aims to understand the physics behind this phenomenon, which has potential industrial applications. Ayah finds the PhD challenging, especially due to the difficulty of maintaining work-life balance. Don’t be scared, she will explain everything! - Recording and editing of the interviews by the PhD students of the Laboratory of Optics and Biosciences.- Upload to MediHal by Elsa BALDUZZ
The Close AGN Reference Survey (CARS) : a comparison between sub-mm and optical AGN diagnostic diagrams
No full textInternational audienceThe LIR –LHCN relation suggests that there is a tight connection between dense gas and star formation. We use data from the Close AGN Reference Survey (CARS) to investigate the dense gas – star formation relation in active galactic nuclei (AGN) hosting galaxies, and the use of dense gas as an AGN diagnostic. Our sample contains five Type-1 (unobscured) AGN that were observed with the Atacama Large Millimetre/submillimetre Array with the aim to detect HCN(4-3), HCO+ (4-3), and CS(7-6). We detect the dense gas emission required for this analysis in three of the five targets. We find that despite the potential impact from the AGN on the line fluxes of these sources, they still follow the LIR –LHCN relation. We then go on to test claims that the HCN/HCO+ and HCN/CS line ratios can be used as a tool to classify AGN in the sub-mm HCN diagram. We produce the classic ionized emission-line ratio diagnostics (the so-called BPT diagrams), using available CARS data from the Multi Unit Spectroscopic Explorer. We then compare the BPT classification with the sub-mm classification made using the dense gas tracers. Where it was possible to complete the analysis we find general agreement between optical and sub-mm classified gas excitation mechanisms. This suggests that AGN can contribute to the excitation of both the low-density gas in the warm ionized medium and the high-density gas in molecular clouds simultaneously, perhaps through X-ray, cosmic ray, or shock heating mechanisms
Excitation of Molecular Hydrogen in Seyferts : NGC 5506 and NGC 3081
No full textInternational audienceWe utilize James Webb Space Telescope (JWST) Mid Infrared Instrument (MIRI) integral field unit observations to investigate the behavior and excitation of H 2 in the nearby Seyfert galaxies NGC 3081 and NGC 5506, both part of the Galactic Activity, Torus, and Outflow Survey (or GATOS). We compare population levels of the S(1) to S(8) rotational H 2 emission lines visible to JWST/MIRI spectroscopy to models assuming local thermodynamic equilibrium (LTE), in order to estimate the column density and thermal scaling of the molecular gas. For the nuclear regions, we incorporate Very Large Telescope Spectrograph for INtegral Field Observations in the Near Infrared (or VLT/SINFONI) K-band observations to estimate population levels for available rovibrational H 2 emission lines, and compare the resultant population curves to non-LTE radiative transfer models and shock modeling. We report a differing set of prominent active galactic nuclei (AGN)-driven excitation mechanisms between the two galaxies. For NGC 3081, we find that a non-LTE radiative transfer environment is adequate to explain observations of the nuclear region, indicating that the primary mode in which the AGN transfers excitation energy is likely irradiation. We estimate the extent of AGN photoionization along the ionization bicone to be ≈330 pc. In contrast, for NGC 5506, we find a shock scenario to be a more plausible excitation mechanism, a conclusion bolstered by an observed spatial correlation between higher-energy rotationa
Neutrinos instables et supernovae à effondrement de cœur
No full textThe discovery of neutrino oscillations demonstrated that (at least two) neutrinos are massive and have non-zero mixing angles, providing evidence of physics beyond the Standard Model. One crucial implication of non-zero neutrino masses is the possibility that massive neutrinos are unstable and decay into lighter particles. Core-collapse supernovae are among the most powerful sources of neutrinos in the Universe. These energetic explosions mark the death of massive stars, releasing most of their gravitational energy as neutrinos. If detected, these neutrinos can provide information about the supernova dynamics or neutrino properties. To date, the observation of supernova neutrinos has been limited to a single event, SN1987A, observed by Kamiokande-II, IMB, and Baksan. Another possibility for observing supernova neutrinos is through the detection of the Diffuse Supernova Neutrino Background (DSNB), representing the flux of neutrinos emitted by all past supernovae in the Universe. Given the large amount of neutrinos emitted and the extreme conditions under which they are produced, core-collapse supernovae and the DSNB provide an excellent laboratory for new physics. This thesis explores the potential impact of neutrino nonradiative decay, either in vacuum or in matter, on the supernova neutrino signal. Considering a three-neutrino framework, we first studied neutrino decay in vacuum and the spectral modifications it induces. We performed the first likelihood analysis of the 24 SN1987A neutrino events to derive limits on the neutrino lifetimes for both normal and inverted mass orderings. While sensitivity to neutrino nonradiative decay is weak for the normal mass ordering, for the inverted mass ordering, we were able to set a lower bound of tau/m > 1.2x10^5 s/eV at 90% CL. In normal ordering, we were unable to improve or reject previous limits. However, our results in inverted ordering significantly improve upon all previous bounds by several orders of magnitude. Only cosmological constraints, which are model-dependent, remain more stringent. In dense environments such as supernovae, matter effects can enhance the interactions of neutrinos into massless Majorons, allowing decay processes in which a neutrino decays into another (anti)neutrino and a massless Majoron. We performed the first likelihood analysis of SN1987A events to constrain these couplings between neutrinos and massless Majorons, considering a three-neutrino framework and recent detailed simulations of SN1987A. Our results provide limits to these couplings, improving upon previous bounds from supernovae and significantly bettering those from lepton or meson decays. Moreover, our limits are competitive with those obtained in neutrinoless double-beta decay experiments. Moreover, we investigated how neutrino decay in matter could impact future supernova observations at next-generation neutrino detectors, such as Hyper-Kamiokande (HK), JUNO, and DUNE, and future dark matter detectors like DARWIN. We obtained prospects for the limits on neutrino-Majoron couplings from upcoming core-collapse events leaving a neutron star or a black hole. We demonstrated that a future galactic core-collapse event will allow us to improve significantly the limits on these couplings. Finally, we provided predictions for the DSNB signal considering neutrino decay in matter. We showed for the first time that this effect could be sizable for a detector such as HK.La découverte des oscillations des neutrinos a démontré que (au moins deux) neutrinos sont massifs et ont des angles de mélange non nuls, fournissant ainsi la preuve d'une physique au-delà du modèle standard. Une implication cruciale des masses non nulles des neutrinos est la possibilité que les neutrinos massifs soient instables et se désintègrent en particules plus légères. Les supernovae à effondrement gravitationnel de coeur comptent parmi les sources de neutrinos les plus puissantes de l'univers. Ces explosions énergétiques marquent la mort d'étoiles massives, libérant la majeure partie de leur énergie gravitationnelle sous forme de neutrinos. S'ils sont détectés, ces neutrinos peuvent fournir des informations sur la dynamique des supernovae ou les propriétés des neutrinos. À ce jour, l'observation des neutrinos de supernova s'est limitée à un seul événement, la SN1987A, observé par Kamiokande-II, IMB et Baksan. Une autre possibilité d'observer les neutrinos de supernova consiste à détecter le fond diffus de neutrinos de supernova (DSNB), qui représente le flux de neutrinos émis par toutes les supernovae passées dans l'Univers. Compte tenu de la grande quantité de neutrinos émis et des conditions extrêmes dans lesquelles ils sont produits, les supernovae à effondrement de coeur et le DSNB constituent des excellents laboratoires pour la nouvelle physique.Cette thèse explore l'impact potentiel de la désintégration non radiative des neutrinos, dans le vide ou dans la matière, sur le signal des neutrinos de supernova. En considérant un cadre à trois neutrinos, nous avons d'abord étudié la désintégration dans le vide et les modifications spectrales qu'elle induit. Nous avons effectué la première analyse de vraisemblance des 24 événements de la SN1987A afin de dériver des limites sur la durée de vie des neutrinos, pour les ordres de masse normal et inversé. Alors que la sensibilité à la désintégration non radiative est faible pour l'ordre normal, pour l'ordre inversé, nous avons pu fixer une limite inférieure de tau/m > 1,2x10^5 s/eV à 90% CL. Dans l'ordre normal, nous n'avons pas pu améliorer ou rejeter les limites précédentes. Cependant, nos résultats dans l'ordre inversé améliorent considérablement toutes les limites précédentes de plusieurs ordres de grandeur. Seules les contraintes cosmologiques, dépendant du modèle, restent plus strictes. Dans des environnements denses tels que les supernovae, les effets de la matière peuvent renforcer les interactions des neutrinos en Majorons sans masse, permettant des processus de désintégration dans lesquels un neutrino se désintègre en un (anti)neutrino et un Majoron sans masse, ou presque. Nous avons réalisé la première analyse de vraisemblance des événements SN1987A afin de limiter ces couplages entre neutrinos et Majorons sans masse, dans un cadre à trois neutrinos et de simulations récentes de SN1987A. Nos résultats fournissent des limites améliorant celles issues des supernovae, et surpassent largement celles obtenues via les désintégrations de leptons ou de mésons. De plus, elles sont compétitives avec celles des expériences de désintégration double-bêta sans neutrinos. Enfin, nous avons étudié comment la désintégration des neutrinos dans la matière pourrait affecter les observations futures de supernovas avec des détecteurs de nouvelle génération, tels que Hyper-Kamiokande (HK), JUNO, DUNE, ainsi que des détecteurs de matière noire comme DARWIN. Nous avons obtenu des contraintes sur les couplages neutrino-Majoron à partir de futurs effondrements de coeur résultant en une étoile à neutrons ou un trou noir. Nous avons démontré qu'un tel événement galactique permettrait d'améliorer considérablement les limites sur ces couplages. Enfin, nous avons fourni des prédictions pour le signal DSNB en considérant de la désintégration des neutrinos dans la matière. Nous avons montré pour la première fois que cet effet pourrait être significatif pour un détecteur comme HK
Detecting and characterising the magnetic field of exoplanets
No full textInternational audienceMagnetic fields play a crucial role in planetary evolution and habitability. While the intrinsic magnetic fields of solar system planets are relatively well understood, the magnetic properties of exoplanets remain largely unconstrained, despite their potential ubiquity. Detecting exoplanetary magnetic fields is essential to advancing our understanding of planetary habitability beyond the solar system. This paper focuses on two promising spectropolarimetric techniques for detecting magnetic fields in hot exoplanets: direct detection through polarization signatures in the He I 1083 nm triplet and indirect detection via star-planet magnetic interactions manifesting as stellar hot spots. The direct method is particularly suited to close-in gas giants, leveraging the Hanle and Zeeman effects to detect low-amplitude magnetic fields. The indirect method can apply to both giant and low-mass planets by identifying magnetic connectivity-induced features in the stellar atmosphere. Although the interpretation of current detections remain tentative, upcoming high-resolution spectropolarimetric capabilities in the UV and near-infrared, particularly with future missions like HWO, promise to enable definitive measurements of exoplanetary magnetic fields. These advancements will open new avenues for probing the magnetic environments of exoplanets and their implications for atmospheric retention and habitability
Searching for substellar companion candidates with Gaia. III. Search for companions to members of young associations
No full textContext. Absolute astrometry with Gaia is expected to detect and characterize the orbits of thousands of exoplanets in the coming years. A tool, GaiaPMEX, was recently developed to characterize multiple systems based on two binarity indicators derived from the DR3 astrometric solution: the astrometric signature α ruwe in linear motion residuals in Gaia-only data, and, when the sources were also observed by Hipparcos, the astrometric signature α PMa in the Gaia-Hipparcos proper motion anomaly (PMa). Aims. Our aim is to identify close (less than typ. 20 au) (sub)stellar companion candidates to star members of close-by young associations previously monitored in radial velocity (RV) surveys. We wish to compare the detection capabilities of absolute astrometry and spectroscopy, and to characterize planetary-mass companions, combining the astrometric data with direct imaging and RV data. Methods. We use GaiaPMEX to identify binary stars members of close young associations and constrain the mass and semi-major axes (sma) of possible companions. For companion masses possibly in the planetary range, we use direct imaging and when possible, RV data as well, to further constrain their nature and orbital properties. Results. For each of our targets, we provide a diagnosis on its binarity based on absolute astrometry. When no binary is detected, GaiaPMEX provides detection limits in the (sma, mass) space. We identify several companions with possible masses down to the brown dwarfs (BD; 50+) or planetary masses (13). Around the M-type star G80-21, we detected a new companion orbiting at less than 1-2 au. Adding RV and high contrast imaging data shows this companion is a giant planet. In other two cases, AB Pic and HD 14082 B, we confirm the presence of substellar companions, and determine the first robust solutions for their mass and orbital properties. We further identified 9 potentially interesting candidates for planetary mass companions, which remain to be studied. Finally, a detailed treatment of noises in Gaia astrometric measurements shows that there are no evidence at a 2-σ level of two exoplanet detections that were previously announced based on the same set of data. Conclusions. Our approach allows to detect all stellar mass companions with sma in the range 0.1-10 au. For separations below 0.1 au, however, spectroscopy outperforms absolute astrometry. Combining GaiaPMEX and RV data is therefore perfectly adapted for a full exploration of the 0.01-10 au sma range when searching for stellar companions, and increases the expected rate of detections derived from RV surveys. Moreover, in the 0.5 to 5 au domain, GaiaPMEX has an excellent sensitivity to BDs, and a good sensitivity to planetary mass planers as well for this sample
Relativistically magnetized collisionless shocks in pair plasma: Solitons, chaos, and thermalization
No full textInternational audienceIn this paper, the first in a series, we present a new theoretical model for the global structure and dissipation of relativistically magnetized collisionless shock waves. Quite remarkably, we find that in contrast to unmagnetized shocks, the leading energy dissipation channel does not involve collective plasma interactions. Rather, it is a consequence of nonlinear particle dynamics. We demonstrate that the kinetic-scale shock transition can be modeled as a stationary system consisting of a large set of cold beams coupled through the magnetic field. The fundamental mechanism governing shock dissipation relies on the onset of chaos in orbital dynamics within quasiperiodic solitonic structures. We discuss the impact of upstream temperature and magnetization on the shock profile, recovering the magnetic field compression, downstream velocities, and heating expected from the Rankine-Hugoniot jump conditions. We deduce a rate of entropy generation from the spectrum of Lyapunov exponents and discuss the thermalization of the beam distribution. Our model provides a general framework to study magnetized collisionless shock structures
Generation of Large-scale Magnetic Fields Upstream of Gamma-Ray Burst Afterglow Shocks
No full textInternational audienceThe origins of the magnetic fields that power gamma-ray burst (GRB) afterglow emission are not fully understood. One possible channel for generating these fields involves the pre-conditioning of the circumburst medium: in the early afterglow phase, prompt photons streaming ahead of the GRB external shock can pair produce, seeding the upstream with drifting electron–positron pairs and triggering electromagnetic microinstabilities. To study this process, we employ 2D periodic particle-in-cell simulations in which a cold electron–proton plasma is gradually enriched with warm electron–positron pairs injected at mildly relativistic speeds. We find that continuous pair injection drives the growth of large-scale magnetic fields via filamentation-like instabilities; the temporal evolution of the field is self-similar and depends on a single parameter, α / ( t f ω pi ) 1 / 2 t ω pi , where α is the ratio of final pair beam density to background plasma density, t f is the duration of pair injection, and ω pi is the plasma frequency of background protons. Extrapolating our results to parameter regimes realistic for long GRBs, we find that upstream pair enrichment generates weak magnetic fields on scales much larger than the proton skin depth; for bright bursts, the extrapolated coherence scale at a shock radius of R ∼ 10 17 cm is λ y ∼ 100 c / ω pi , and the corresponding magnetization is σ ∼ 10 −8 for typical circumburst parameters. These results may help explain the persistence of magnetic fields at large distances behind GRB shocks
Detection of triboelectric discharges during dust events on Mars
No full textInternational audienceLightning is among the most energetic manifestation of electrical activity in planetary atmospheres, with documented observations not only on Earth but also on Saturn and Jupiter. On Mars, the existence of electrical activity has long been suspected but never directly demonstrated. The dusty atmosphere of Mars undergoes aeolian processes, ranging from wind-blown dust and sand, metre-to-hundred-metre-sized dust devils to thousand-kilometre-scale dust storms, which, in Earth’s deserts, can become electrified through triboelectric charging. For this reason, electric fields have been predicted to build up on Mars, but with no measurement of Martian atmospheric electrical activity so far. Here we report in situ detections of triboelectric discharges, identified by their electrical and acoustic signatures captured by the SuperCam microphone aboard the Perseverance rover. Fifty-five events have been detected over two Martian years, usually associated with dust devils and dust storm convective fronts. These serendipitous observations demonstrate that Martian electric fields can reach the breakdown threshold of the near-surface atmosphere of Mars, predicted to be on the order of several tens of kV m−1. Such electrical activity could affect dust dynamics and potentially fuel a reactive electrochemical environment enhancing the oxidizing capacity of the atmosphere, with consequences for the preservation of organic molecules. This in situ evidence may have implications for surface chemistry, habitability and human exploration