HAL-OBSPM
Not a member yet
37663 research outputs found
Sort by
RAMCOAL: Tracking on-the-fly massive black hole binary evolution and coalescence in galaxy simulations
No full textInternational audienceThe detection of gravitational waves (GWs) from massive black hole binary (MBHB) coalescence motivates the development of a subgrid model. We present RAMCOAL, integrated into the RAMSES code, which simulates the orbital evolution of MBHBs, while accounting for stellar and gaseous dynamical friction (DF), stellar scattering, circumbinary disk interactions, and GW emission at scales below the simulation resolution. Unlike post-processing approaches, RAMCOAL tracks the real-time evolution of MBHBs within hydrodynamical simulations of galaxies using local quantities to model the dynamics and accretion. This approach enables more accurate predictions of the GW signals and the properties of merging black holes. We validated RAMCOAL across isolated and merging galaxy setups at resolutions of 10, 50, and 100 pc, with and without black hole accretion and feedback. In addition, we tested the model in seven galaxy merger scenarios at 100 pc resolution. These tests demonstrated that RAMCOAL is largely resolution-independent and successfully captures the effects of DF from stars, dark matter, and gas, loss-cone scattering, viscous drag from circumbinary disks, and GW emission – all within a realistic galactic environment even at low resolution. With RAMCOAL, we can better estimate MBHB coalescence rates and the GW background, while providing insights into the electromagnetic counterparts of GW sources. This approach bridges the gap between electromagnetic observations and GW detection, offering a more comprehensive understanding of MBHB evolution in cosmological simulations
Spectral Study of Five Major Impact Basins and Their Volcanic Infills on Mercury: A Window Into the Mantle's Properties
No full textInternational audienceNASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission has revealed that about 27% of the surface of Mercury is covered by smooth plains, which are mostly volcanic in origin. These plains are mainly located in the northern hemisphere, as well as within and around major impact basins. We used Mercury Atmospheric and Surface Composition Spectrometer data to perform an exhaustive spectral analysis of five major impact basins: Caloris, Rembrandt, Beethoven, Tolstoj, and Rachmaninoff. We highlighted the existence of a new high-reflectance spectral unit, that had previously only been identified within the Rembrandt basin, as a major unit being more widespread. We named this new unit Young High-reflectance Red Plains. We found a common sequence of volcanic episodes that infilled the basins and shaped their current surface spectral properties. We have shown that the size of the basin and the age of the volcanic infills are likely important parameters for the layering of different volcanic plains, defining the surface spectral units. Our study gives access to mantle properties, and we suggest that heterogeneity in the mantle is certainly not necessary to explain the spectral properties of effusive volcanism associated with impact basins. Future observations by the ESA-JAXA-BepiColombo mission are eagerly awaited to better constrain the planet's spectral, compositional, morphological, and geophysical surface properties
Deimos photometric properties: Analysis of 20 years of observations (2004-2024) by the Mars Express HRSC camera
No full textInternational audienceThe goal of this study is to analyze the photometric properties of Deimos using observations obtained by the Mars Express (MEX) mission while aiming to improve the photometric properties and provide new insights into the texture and composition of the surface of the smallest Martian moon. The findings also support the Martian Moon eXploration mission (MMX) observations. Methods. We analyzed the data obtained by the High Resolution Stereo Camera (HRSC) and the Super Resolution Channel (SRC) on board MEX. The HRSC data, obtained through the use of four filters (blue, green, red, and IR) have a spatial resolution ranging from 390 to 800 m/px. In comparison, the SRC panchromatic data have a resolution ranging from 85 to 300 m/px. The SRC data are of particular interest due to their coverage of a wide range of phase angles, including the opposition effect of Deimos (0.06-138°). Observations of both HRSC and SRC cover only the Mars-facing side of Deimos. As the SRC camera was never absolutely calibrated before and during the MEX mission, we performed the first absolute calibration of the SRC using observations of Jupiter and stars. We then performed a disk-integrated and disk-resolved photometric analysis using the Hapke model. Results. The Deimos surface is dark and predominantly backscattering. The single-scattering albedo (SSA) value (between 6.8% and 7.5%, depending on the model) is similar to the one derived from Phobos. The Deimos phase curve shows a strong opposition effect due to shadow hiding, with almost no effect of the coherent-backscattering process. The amplitude and the half-width of the shadow-hiding opposition surge were found to be 2.14 ± 0.14 and 0.065 ± 0.004, respectively. We found a very high porosity of 86% at the top-layer surface (∼ 10 µm), consistent with the tentative presence of complex-shaped grains or fractal aggregates. Such a high porosity would likely also indicate the presence of a thick dust layer. We did not observe significant variations of the opposition surge across the surface. We observed a blue unit on Deimos in a similar way to Phobos, located on the streamers, which themselves are on the equatorial ridge. The Deimos blue unit exhibits variations relative to its average surface that are similar to those of the blue unit on Phobos, characterized by an average reflectance increase of about 35% (and up to 58%) and a spectral slope decrease of 50%. This blue unit may be due to a different texture of the surface between the two units, with a finer grain and/or a higher porosity. In contrast to the "blue unit" photometric behavior exhibited by Phobos on several crater rims, no such behavior has been observed for Deimos. Conclusions. The Deimos photometric properties, including the SSA, opposition surge, and phase integral, are very similar to Phobos. The presence of a blue unit on Deimos reinforces the idea that the Martian moons have a common origin. The capture of two different bodies with similar spectroscopic and photometric properties appears very unlikely
Euclid Quick Data Release (Q1): Euclid spectroscopy of QSOs. 1. Identification and redshift determination of 3500 bright QSOs
No full textInternational audienceThe slitless spectroscopy mode of the NISP onboard Euclid has enabled efficient spectroscopy of objects within a large FoV. We present a large and homogeneous sample of bright quasars identified from the Euclid Quick Data Release (Q1) by combining high-purity candidate selections from Gaia and WISE with the NISP spectra. Through visual inspection of the Euclid spectra of these quasar candidates, we identify approximately 3500 quasars with reliable redshifts at . We generate the first Euclid composite spectrum of quasars covering rest-frame NUV to NIR wavelengths without telluric lines, which will be pivotal to NIR quasar spectral analysis. We obtain an empirical spectroscopic depth of and at the sensitivity of the Wide Field Survey, beyond which the number of securely identified quasars declines sharply. We analyse VIS morphologies using Sersic and CAS metrics, and a deep-learning PSF fraction to track nuclear dominance. At low redshift (), obvious host structures are common and a single Sersic model fits about half of the sources; at intermediate redshift (), the nuclear component dominates, with 90% of the Sersic fits saturating at the upper index limit. In this intermediate redshift regime, is available, and we use it as a more reliable compactness measure than the single-Sersic and CAS parameters to quantify nuclear versus host emission. We also explore the novel Euclid NIR colour space and discuss the role of these quasars in refining AGN selection techniques for future Euclid data releases. Our results highlight the potential of Euclid spectroscopy to advance quasar surveys and enable the construction of more complete AGN catalogues. The spectroscopic bright quasar catalogue of this work, and the composite quasar spectrum, will be available at https://cdsarc.cds.unistra.fr/. (abridged
Sky Localization of Massive Black Hole Binaries with LISA: Applying Coronagraphic Time-delay Interferometry to Low-latency Searches
No full textInternational audienceThe Laser Interferometer Space Antenna (LISA) will be a space-borne gravitational wave (GW) detector to be launched in the next decade. Central to LISA data analysis is time-delay interferometry (TDI), a numerical procedure which drastically reduces otherwise overwhelming laser frequency noise. LISA data analysis is usually performed on subsets of TDI variables which form a basis e.g., Michelson variables or quasiorthogonal variables . We investigate a less standard TDI variable, denoted , which depends on time and two parameters . For any GW source located at sky position , has the singular property of canceling GW signal when tend to , very much like a coronagraph. Thanks to this property, coronagraphic TDI has the potential to be an efficient model-agnostic method for sky localization of GW sources with LISA. These characteristics make it relevant for low-latency searches of sources with a high multi-messenger potential, such as Massive Black Hole Binaries (MBHBs). Building upon previous theoretical work, and a first assessment of the sky localization capabilities of in the current LISA configuration, we investigate a sky localization algorithm based on coronagraphic TDI. We discuss the results in the context of the accuracy required by facilities susceptible of detecting electromagnetic counterparts emitted by such sources
Investigating the bulge morphology of dual AGN host galaxies from the gothic survey
No full textInternational audienceWe present a structural analysis of bulges in dual active galactic nuclei (AGNs) host galaxies. Dual AGNs arise in galaxy mergers where both supermassive black holes are actively accreting. The AGNs are typically embedded in compact bulges, which appear as luminous nuclei in optical images. Galaxy mergers can result in bulge growth, often via star formation. The bulges can be discy (pseudo-bulges), classical bulges, or belong to elliptical galaxies. Using Sloan Digital Sky Survey Data Release 18 gri images and galfit modelling, we performed 2D decomposition for 131 dual AGNs bulges (comprising 61 galaxy pairs and 3 galaxy triplets) identified in the gothic survey. We derived Sérsic indices, luminosities, masses, and scale lengths of the bulges. Most bulges (105/131) are classical, with Sérsic indices lying between and . Among these, 64 per cent are elliptical galaxies, while the remainder are classical bulges in disc galaxies. Only per cent of the sample exhibits pseudo-bulges. Bulge masses span to , with the most massive systems being ellipticals. Galaxy-type matching shows that elliptical–elliptical and elliptical–disc mergers dominate over disc–disc mergers. At least one galaxy in two-thirds of the dual AGN systems is elliptical and only per cent involve two disc galaxies. Although our sample is limited, our results suggest that dual AGNs preferentially occur in evolved, red, quenched systems, which typically form via major mergers. They are predominantly hosted in classical bulges or elliptical galaxies rather than star-forming disc galaxies
JWST reveals the diversity of nuclear obscuring dust in nearby AGN : nuclear isolation of MIRI/MRS data cubes and continuum spectral fitting
No full textInternational audienceWe investigate the capabilities of the mid-infrared instrument (MIRI) of JWST to advance our knowledge of active galactic nucleus (AGN) dust using the spectral fitting technique on an AGN collection of 21 nearby (z<0.05) AGN (7 type-1 and 14 type-2) observations obtained with the medium resolution spectroscopy (MRS) mode. This collection includes publicly available AGN and data from the collaboration of Galactic Activity, Torus, and Outflow Survey (GATOS). We developed a tool named MRSPSFisol that decomposes MRS cubes into point-like and extended contributions. We found statistically good fits for 12 targets with current AGN dust models. The model that provides good fits (\rm {\chi ^2/dof< 2}) for these 12 targets assumes a combination of clumpy and smooth distribution of dust in a flare-disc geometry where the dust grain size is a free parameter. Still, two and one AGN statistically prefer the disc wind and the classical clumpy torus model, respectively. However, the currently available models fail to reproduce 40 per cent of the targets, likely due to the extreme silicate features not well reproduced by the models and signatures of water-ice and aliphatic hydrocarbon absorption features in most targets. New models exploring, for instance, new chemistry, are needed to explain the complexity of AGN dust continuum emission observed by JWST
Hydrogènoïdes en mécanique classique et quantique (équation de Schrödinger), et applications aux diagnostics de l'atmosphère du Soleil
No full textMasterNous présentons dans ce cours de niveau M1 la théorie des hydrogénoïdes (atomes à électron unique comme Hydrogène ou Hélium ionisé) en mécanique classique (section 1), puis en résolvant l’équation de Schrödinger en mécanique quantique (section 2). Les transitions entre niveaux d’énergie discrets donnent naissance aux raies spectrales dont l’étude permet des diagnostics fondamentaux sur la structure et la stratification en altitude de l’atmosphère solaire, que nous décrivons (section 3). Les observations étagées en température des instruments au sol ou dans l’espace, entre 10000 K et 100000 K, donnent accès à des couches d’altitude variées de la chromosphère et de la zone de transition chromosphère couronne
Euclid preparation. Controlling angular systematics in the Euclid spectroscopic galaxy sample
No full textInternational audienceWe present the strategy to identify and mitigate potential sources of angular systematics in the Euclid spectroscopic galaxy survey, and we quantify their impact on galaxy clustering measurements and cosmological parameter estimation. We first survey the Euclid processing pipeline to identify all evident, potential sources of systematics, and classify them into two broad classes: angular systematics, which modulate the galaxy number density across the sky, and catastrophic redshift errors, which lead to interlopers in the galaxy sample. We then use simulated spectroscopic surveys to test our ability to mitigate angular systematics by constructing a random catalogue that represents the visibility mask of the survey; this is a dense set of intrinsically unclustered objects, subject to the same selection effects as the data catalogue. The construction of this random catalogue relies on a detection model, which gives the probability of reliably measuring the galaxy redshift as a function of the signal-to-noise ratio (S/N) of its emission lines. We demonstrate that, in the ideal case of a perfect knowledge of the visibility mask, the galaxy power spectrum in the presence of systematics is recovered, to within sub-percent accuracy, by convolving a theory power spectrum with a window function obtained from the random catalogue itself. In the case of only approximate knowledge of the visibility mask, we test the stability of power spectrum measurements and cosmological parameter posteriors by using perturbed versions of the random catalogue. We find that significant effects are limited to very large scales, and parameter estimation remains robust, with the most impacting effects being connected to the calibration of the detection model
