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Reconciling PTA and JWST and preparing for LISA with POMPOCO: a Parametrisation Of the Massive black hole POpulation for Comparison to Observations
No full textInternational audienceWe develop a parametrised model to describe the formation and evolution of massive black holes, designed for comparisons with both electromagnetic and gravitational wave observations. Using an extended Press-Schechter formalism, we generate dark matter halo merger trees. We then seed and evolve massive black holes through parameterised prescriptions. This approach, which avoids solving differential equations, is computationally efficient, enabling us to analyse observational data and infer the parameters of our model in a fully Bayesian framework. We find that observations of the black hole luminosity function are compatible with the nHz gravitational wave signal (likely) measured by PTAs, provided we allow for an increased luminosity function at high redshift (), as recently suggested by JWST observations. Our model can simultaneously reproduce the bulk of the relation at , as well as its outliers, something cosmological simulations struggle to do. The inferred model parameters are consistent with expectations from observations and more complex simulations: They favour heavier black hole seeds and short delays between halo and black hole mergers, while requiring supper-Edington accretion episodes lasting a few tens of million years, which in our model are linked to galaxy mergers. We find accretion to be suppressed in the most massive black holes below , consistently with the anti-hierarchical growth hypothesis. Finally, our predictions for LISA, although fairly broad, are in agreement with previous models. Our model offers a new perspective on the apparent tensions between the black hole luminosity function and the latest JWST and PTA results. Its flexibility makes it ideal to fully exploit the potential of future gravitational wave observations of massive black hole binaries with LISA
Gravitational collapse of anisotropic cylindrical shearfree fluids with new exact interior solutions of GR
No full textInternational audienceWe present a study of shearfree gravitational collapse using cylindrically symmetric spacetimes whose interior is a non-rotating dissipative fluid bounded by a cylindrical hypersurface beyond which is an Einstein-Rosen vacuum exterior. We consider three different pressure configurations: axially, azimuthally, and radially directed, for which we find new exact interior solutions of the field equations. We show that the matching conditions cannot be satisfied by the fluid with radial pressure, while the axial and azimuthal cases with a lapse function depending only on the time coordinate do satisfy these constraints. We derive, for both cases, a sufficient condition for an emission of gravitational radiation from the interior towards the exterior, We therefore show that, at variance with what happens for spherical symmetry, in the simplified picture of an infinite cylinder of anisotropic shearfree matter, gravitational waves can be emitted during collapsing motion
The impact on astrometry by solar-wind effect in pulsar timing
No full textInternational audienceAstrometry of pulsars, particularly their distances, serves as a critical input for various astrophysical experiments using pulsars. Pulsar timing is a primary approach for determining a pulsar's position, parallax, and distance. In this paper, we explore the influence of the solar wind on astrometric measurements obtained through pulsar timing, focusing on its potential to affect the accuracy of these parameters. Using both theoretical calculation and mock-data simulations, we demonstrate a significant correlation between the pulsar position, annual parallax and the solar-wind density parameters. This correlation strongly depends on the pulsar's ecliptic latitude. We show that fixing solar-wind density to an arbitrary value in the timing analysis can introduce significant bias in the estimated pulsar position and parallax, and its significance is highly dependent on the ecliptic latitude of the pulsar and the timing precision of the data. For pulsars with favourable ecliptic latitude and timing precision, the astrometric and solar-wind parameters can be measured jointly with other timing parameters using single-frequency data. The parameter correlation can be mitigated by using multi-frequency data, which also significantly improves the measurement precision of these parameters; this is particularly important for pulsars at a medium or high ecliptic latitude. Additionally, for a selection of pulsars we reprocess their EPTA Data Release 2 data to include modelling of solar-wind effect in the timing analysis. This delivers significant measurements of both parallax and solar-wind density, the latter of which are consistent with those obtained at low-frequency band. In the future, combining pulsar timing data at gigahertz and lower frequencies will probably deliver the most robust and precise measurements of astrometry and solar wind properties in pulsar timing
Investigating the formation and growth of Titan's atmospheric aerosols using an experimental approach
No full textInternational audienceTitan has a climate system with similarities to Earth, including the presence of a thick atmosphere made up of several atmospheric layers. As on Earth, Titan's climate is influenced by several factors: the gaseous species making up the atmosphere, the energy deposited on the satellite, and solid organic aerosols. Indeed, numerous observations have revealed the presence of solid particles in the form of an opaque orange haze in Titan's atmosphere, influencing radiation balance and atmospheric dynamics, for example. However, the influence of these suspended solid particles seems to evolve according to the atmospheric altitude where they are located, certainly testifying to the presence of organic solids with different physico-chemical properties. At present, it is suspected that several populations/classes of atmospheric aerosols may form following different chemical pathways, and that aerosols undergo growth processes that modify their properties. In this experimental study, we present new observations on the evolution of morphological and chemical properties observed on Titan aerosol analogues, produced from a mixture of 20 % CH4 and 80 % N2 injected into a dusty RF plasma experiment. Using SEM (morphological) and FTICR-LDI-MS (chemical composition) analyses, we observe that properties evolve according to certain formation and growth mechanisms, which differentiate over time. The evolution of the neutral gaseous chemical composition analyzed in-situ by QMS in parallel shows correlations with the evolution of solid properties, testifying to the selective involvement of certain neutral products in the formation and growth mechanisms of solid aerosols. By linking the analyses of the gas phase and organic solids, we propose the calculation of an uptake coefficient between six neutral gaseous products (C2H2, HCN, C2H6, C2H3N, HC3N, C2N2) and the surface of the Titan aerosol analogues produced in this study
A Java library to perform S-expansions of Lie algebras
No full textInternational audienceThe contraction method is a procedure that allows to establish non-trivial relations between Lie algebras and has had succesful applications in both mathematics and theoretical physics. This work deals with generalizations of the contraction procedure with a main focus in the so called S-expansion method as it includes most of the other generalized contractions. Basically, the S-exansion combines a Lie algebra with a finite abelian semigroup in order to define new S-expanded algebras. After giving a description of the main ingredients used in this paper, we present a Java library that automatizes the S-expansion procedure. With this computational tool we are able to represent Lie algebras and semigroups, so we can perform S-expansions of Lie algebras using arbitrary semigroups. We explain how the library methods has been constructed and how they work; then we give a set of example programs aimed to solve different problems. They are presented so that any user can easily modify them to perform his own calculations, without being necessarily an expert in Java. Finally, some comments about further developements and possible new applications are made
THE NEXT GENERATION VIRGO CLUSTER SURVEY. XXII. SHELL FEATURE EARLY-TYPE DWARF GALAXIES IN THE VIRGO CLUSTER
No full textInternational audienceThe Next Generation Virgo Cluster Survey is a deep (with a 2sigma detection limit mug = 29 mag arcsec-2 in the g-band) optical panchromatic survey targeting the Virgo cluster from its core to virial radius, for a total areal coverage of 104 square degrees. As such, the survey is well suited for the study of galaxies' outskirts, haloes, and low surface brightness features that arise from dynamical interactions within the cluster environment. We report the discovery of extremely faint (mug > 25 mag arcsec-2) shells in three Virgo cluster early-type dwarf galaxies: VCC 1361, VCC 1447, and VCC 1668. Among them, VCC 1447 has an absolute magnitude Mg = -11.71 mag and is the least massive galaxy with a shell system discovered to date. We present a detailed study of these low surface brightness features. We detect between three and four shells in each of our galaxies. Within the uncertainties, we find no evidence of a color difference between the galaxy main body and shell features. The observed arcs of the shells are located up to several effective radii of the galaxies. We further explore the origin of these low surface brightness features with the help of idealized numerical simulations. We find that a near equal mass merger is best able to reproduce the main properties of the shells, including their quite symmetric appearance and their alignment along the major axis of the galaxy. The simulations provide support for a formation scenario in which a recent merger, between two near-equal mass, gas-free dwarf galaxies, forms the observed shell systems
Holographic confining theories on space-times with constant positive curvature
No full textInternational audienceVarying the curvature, quantum phase transitions are investigated in holographic confining QFTs defined on a fixed constant positive curvature background. We find a competition between two branches of solutions and a phase transition as one varies the space-time curvature. The low-curvature phase has the same kind of IR geometry as the flat-space solution, while the high-curvature phase has a regular interior. We argue that, depending on the leading asymptotic exponent of the scalar potential, the transition may be first-order or higher-order
Euclid: A complete Einstein ring in NGC 6505
No full textInternational audienceWe report the discovery of a complete Einstein ring around the elliptical galaxy NGC 6505, at . This is the first strong gravitational lens discovered in Euclid and the first in an NGC object from any survey. The combination of the low redshift of the lens galaxy, the brightness of the source galaxy ( lensed, unlensed), and the completeness of the ring make this an exceptionally rare strong lens, unidentified until its observation by Euclid. We present deep imaging data of the lens from the Euclid Visible Camera (VIS) and Near-Infrared Spectrometer and Photometer (NISP) instruments, as well as resolved spectroscopy from the Keck Cosmic Web Imager (KCWI). The Euclid imaging in particular presents one of the highest signal-to-noise ratio optical/near-infrared observations of a strong gravitational lens to date. From the KCWI data we measure a source redshift of . Using data from the Dark Energy Spectroscopic Instrument (DESI) we measure a velocity dispersion for the lens galaxy of . We model the lens galaxy light in detail, revealing angular structure that varies inside the Einstein ring. After subtracting this light model from the VIS observation, we model the strongly lensed images, finding an Einstein radius of 2.5 arcsec, corresponding to at the redshift of the lens. This is small compared to the effective radius of the galaxy, . Combining the strong lensing measurements with analysis of the spectroscopic data we estimate a dark matter fraction inside the Einstein radius of and a stellar initial mass-function (IMF) mismatch parameter of , indicating a heavier-than-Chabrier IMF in the centre of the galaxy
High resolution spectra of the [6297-6303] and [6361-6367] Angström domains (including forbidden OI lines) of the Sun and brightest stars
No full textWe present a dataset of high resolution spectra of the Sun and ten bright stars of the domains [6297-6303] and [6361-6367] Angtröm. Solar spectra were obtained in the quiet Sun at various distances from disk centre with the ground based Meudon Solar Tower and Themis telescope (12 mÅ resolution) and with the Solar Optical Telescope (SOT) onboard the Hinode satellite (21 mÅ resolution). Spectra of 10 bright stars (magnitude < 2) were also got with Themis at 12 mÅ resolution. These spectral domains contain the faint and forbidden OI lines (6300.31 Å and 6363.79 Å) that are useful for the research of Oxygen abundance. The spectra shown here are freely available in FITS format to the research community
Search for electroweak-scale dijet resonances using trigger-level analysis with the ATLAS detector in fb of collisions at TeV
No full textInternational audienceThis article reports on a search for dijet resonances using fb of collision data recorded at TeV by the ATLAS detector at the Large Hadron Collider. The search is performed solely on jets reconstructed within the ATLAS trigger to overcome bandwidth limitations imposed on conventional single-jet triggers, which would otherwise reject data from decays of sub-TeV dijet resonances. Collision events with two jets satisfying transverse momentum thresholds of GeV and jet rapidity separation of are analysed for dijet resonances with invariant masses from to GeV. A data-driven background estimate is used to model the dijet mass distribution from multijet processes. No significant excess above the expected background is observed. Upper limits are set at confidence level on coupling values for a benchmark leptophobic axial-vector model and on the production cross-section for a new resonance contributing a Gaussian-distributed line-shape to the dijet mass distribution