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On the origin of the Σ<sub>1</sub>-M<sub>⋆</sub> quenching boundary
No full textInternational audienceWe have considered a phenomenologically motivated model in which galaxies are quenched when the energy output of the central black hole exceeds a hundred times the gravitational binding energy of the baryons in the host halo. The model reproduces the mass functions of star-forming and quiescent galaxies at and the quenching boundary on a - diagram. The quenching boundary arises because of the colour-morphology relation. The stellar surface density in the central kiloparsec is a morphological indicator. Galaxies becomes redder as increases until they cross the quenching boundary and enter the passive population. Mergers drive the growth of supermassive black holes and the morphological evolution that accompany the migration to the red sequence. That is the origin of the population of high-mass passive galaxies. At lower masses, passive galaxies are mainly satellites that ceased to form stars because of environmental effects
Quasar radiation transforms the gas in a merging companion galaxy
No full textInternational audienceQuasars, powered by gas accretion onto supermassive black holes1,2, rank among the most energetic objects in the Universe3,4. Although they are thought to be ignited by galaxy mergers5, 6, 7, 8, 9, 10–11 and affect the surrounding gas12, 13, 14–15, observational constraints on both processes remain scarce16, 17–18. Here we describe a major merging system at redshift z ≈ 2.7 and demonstrate that radiation from the quasar in one galaxy directly alters the gas properties in the other galaxy. Our findings reveal that the galaxies, with centroids separated by only a few kiloparsecs and approaching each other at a speed of approximately 550 km s‑1, are massive, are forming stars and contain a substantial molecular mass. Yet, dusty molecular gas seen in absorption against the quasar nucleus is highly excited and confined within cloudlets with densities of approximately 105 to 106 cm‑3 and sizes of less than 0.02 pc, several orders of magnitude more compact than those observed in intervening (non-quasar) environments. This is also approximately 105 times smaller than currently resolvable through molecular-line emission at high redshifts. We infer that, wherever it is exposed to the quasar radiation, the molecular gas is disrupted, leaving behind surviving dense clouds too small to give birth to new stars. Our results not only underscore the role of major galaxy mergers in triggering quasar activity but also reveal localized negative feedback as a profound alteration of the internal gas structure, which probably hampers star formation
Near-field imaging of local interference in radio interferometric data: Impact on the redshifted 21 cm power spectrum
No full textInternational audienceRadio-frequency interference (RFI) is a major systematic limitation in radio astronomy, particularly for science cases requiring high sensitivity, such as 21 cm cosmology. Traditionally, RFI is dealt with by identifying its signature in the dynamic spectra of visibility data and flagging strongly affected regions. However, for RFI sources that do not occupy narrow regions in the time-frequency space, such as persistent local RFI, modeling these sources could be essential to mitigating their impact. This paper introduces two methods for detecting and characterizing local RFI sources from radio interferometric visibilities: matched filtering and maximum a posteriori (MAP) imaging. These algorithms use the spherical wave equation to construct three-dimensional near-field image cubes of RFI intensity from the visibilities. The matched filter algorithm can generate normalized maps by cross-correlating the expected contributions from RFI sources with the observed visibilities, while the MAP method performs a regularized inversion of the visibility equation in the near field. We developed a full polarization simulation framework for RFI and demonstrated the methods on simulated observations of local RFI sources. The stability, speed, and errors introduced by these algorithms were investigated, and, as a demonstration, the algorithms were applied to a subset of NenuFAR observations to perform spatial, spectral, and temporal characterization of two local RFI sources. We used simulations to assess the impact of local RFI on images, the uv plane, and cylindrical power spectra, and to quantify the level of bias introduced by the algorithms in order to understand their implications for the estimated 21 cm power spectrum with radio interferometers. The near-field imaging and simulation codes are publicly available in the Python library nfis
On the spectra of holographic QFTs on constant curvature manifolds
No full textInternational audienceWe analyze linear fluctuations of five-dimensional Einstein-Dilaton theories dual to holographic quantum field theories defined on four-dimensional de Sitter and Anti-de Sitter space-times. We identify the physical propagating scalar and tensor degrees of freedom. For these, we write the linearized bulk field equations as eigenvalue equations. In the dual QFT, the eigenstates correspond to towers of spin-0 and spin-2 particles propagating on associated to gauge-invariant composite states. Using particular care in treating special ``zero-modes,'' we show in general that, for negative curvature, the particle spectra are always discrete, whereas for positive curvature they always have a continuous component starting at , where is the radius. We numerically compute the spectra in a concrete model characterized by a polynomial dilaton bulk potential admitting holographic RG-flow solutions with a UV and IR fixed points. In this case, we find no discrete spectrum and no perturbative instabilities
Hidden magnetic fields of the quiet Sun derived from Hanle depolarization of lines of the "second solar spectrum" at the limb from Pic du Midi observations
No full textThis paper is based on a dataset of many strongly polarized solar lines belonging to the "second solar spectrum", i.e. the spectrum near the limb in linear scattering polarization. The observations were done at the Pic du Midi Turret Dome in 2006. The solar spectra were recorded at high spectral resolution (R = 400000) with the spectrograph slit orthogonal to the solar limb, so that µ = cosθ continuously varied from 0 .0 to 0.45. The crystal liquid polarimeter delivered the linear polarization rate (Q/I). Strong lines such as CaII 3934 Å, CaI 4227 Å, SrI 4607 Å, SrII 4078 Å, BaII 4554 Å were studied. We measured the Hanle depolarization with the help of models predicting the polarization envelope with no magnetic field and we got values in the range 13-25 Gauss for the unresolved turbulent magnetic field, and we found that it often decreases towards the limb, revealing an altitude gradient. This present analysis was not yet published and spectra shown here become freely available to the research community
Probing gravity with non-linear clustering in redshift space
No full textInternational audienceWe present the first computation of the gravity model testing parameter on realistic simulated modified gravity galaxy mocks. The analysis is conducted using two twin simulations presented in arXiv:1805.09824(1): one based on general relativity (GR) and the other on the Hu Sawicki model with (F5). This study aims to measure the estimator in GR and models using high-fidelity simulated galaxy catalogs, with the goal of assessing how future galaxy surveys can detect deviations from standard gravity. Deriving this estimator requires precise, unbiased measurements of the growth rate of structure and the linear galaxy bias. We achieve this by implementing an end-to-end cosmological analysis pipeline in configuration space, using the multipoles of the 2-point correlation function. Our analysis demonstrates how to measure the scale-dependent growth rate predicted by non-standard gravity models. We split the estimation of the RSD parameter over distinct scale ranges, separating large (quasi-linear) and small (non-linear) scales. We show that this estimator can be accurately measured using mock galaxies in low redshift bins (), where it offers strong discriminating power over competing gravity theories. We find that, for an all-sky galaxy survey and neglecting observational systematics, accurate and largely unbiased estimations of can be obtained across all redshifts. However, the error bars are too large to clearly distinguish between the theories. When measuring the scale-dependence of the estimator, we note that state-of-the-art theory modeling limitations and intrinsic "prior volume effects" prevent high-accuracy constraints. Alternatively, we propose a null test of gravity using RSD clustering, which, if small scales are modeled accurately in future surveys, could detect significant departures from GR
The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics
No full textInternational audienceThe standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. [Abridged
The atmosphere of Titan in late northern summer from JWST and Keck observations
No full textInternational audienceSaturn's moon Titan undergoes a long annual cycle of 29.45 Earth years. Titan's northern winter and spring were investigated in detail by the Cassini-Huygens spacecraft (2004-2017), but the northern summer season remains sparsely studied. Here we present new observations from the James Webb Space Telescope (JWST) and Keck II telescope made in 2022 and 2023 during Titan's late northern summer. With JWST's Mid-Infrared Instrument we spectroscopically detected the methyl radical, the primary product of methane breakup and key to the formation of ethane and heavier molecules. With JWST's Near Infrared Spectrograph we detected several non-LTE CO and CO2 emission bands that allow measurement of these species over a wide altitude range. Lastly, with JWST's Near Infrared Camera and Keck II we imaged northern hemisphere tropospheric clouds evolving in altitude, providing new insights and constraints on seasonal convection patterns. These observations pave the way for new observations and modeling of Titan's climate and meteorology as it progresses through northern Fall equinox, when its atmosphere is expected to show dramatic seasonal changes
Étude de la reconnexion magnétique du côté jour en présence d'ions froids et de champ guide
No full textDepending on the orientation of the interplanetary magnetic field (IMF) transported by the solar wind, the magnetic field lines of the Earth's magnetic field can reconnect with those of the IMF at the dayside magnetopause, the boundary between the solar wind and the Earth's magnetic field. As the plasma conditions on each side of the magnetopause are different, the magnetic reconnection is called asymmetric. The reconnection process starts in a diffusion region at electron scales and generates fast diverging electron and ion jets. The boundaries separating the plasma flowing into the reconnection region from the outflow plasma are called the separatrices. This PhD thesis investigates in detail the structure of the magnetospheric separatrix far from the diffusion region in the presence of magnetospheric cold ions, a high density gradient and a moderate guide field. Using in-situ measurements of the NASA Magnetospheric Multiscale(MMS) mission and fully kinetic 2D Particle-In-Cell (PIC) simulations obtained from the open source SMILEI code, the current densities, electric and magnetic signatures as well as energy conversion processes are investigated. From in-situ measurements at the separatrix, the current density is found dominated by the ion diamagnetic current and the normal electric field sustained by the drift of the cold ions in agreement with the simulations. The energy conversion in the fluid frame is ensured by the parallel current and the electric field produced by the parallel electron pressure term. The partitioning of the energy between ions and electrons is discussed based on the pressure strain calculations. From the kinetic simulations performed with and without cold ions, and with and without guide field, it is found that with a guide field, the presence of cold ions reinforces the electron pressure gradient reducing the normal electric field and increasing the motion of the reconnection region. All these effects modify the energy and plasma exchanges between the solar wind and the Earth's magnetosphere.En fonction de l'orientation du champ magnétique interplanétaire (CMI) transporté par le vent solaire, les lignes du champ magnétique terrestre peuvent se reconnecter à celles du CMI sur le côté jour de la magnétopause, la frontière entre le vent solaire et le magnétique terrestre. Les conditions de plasma étant différentes de chaque côté de la magnétopause, la reconnexion magnétique est dite asymétrique. Le processus de reconnexion débute dans une région de diffusion aux échelles électroniques et produit des jets d'électrons et d'ions divergents. Les frontières séparant le plasma qui s'écoule vers la région de reconnexion de celui qui s'en éloigne sont appelées séparatrices. Cette thèse de doctorat étudie en détail la structure la séparatrice magnétosphérique loin de la région de diffusion en présence d'ions froids magnétosphériques, d'un fort gradient et d'un champ guide modéré. A partir des mesures in situ de la mission Magnetospheric Multiscale (MMS) de la NASA et de simulations 2D complètement cinétiques de type "Particle-In-Cell" (PIC) obtenues à partir du code en accès libre SMILEI, les densités de courant, les signatures électriques et magnétiques ainsi que les processus de conversion d'énergie sont étudiés. A partir des mesures in situ à la séparatrice, il est trouvé que la densité de courant est dominée par le courant diamagnétique des ions et que le champ électrique normal est soutenu par le mouvement des ions froids en accord avec les simulations. La conversion d'énergie dans le repère du plasma est assurée par le courant parallèle et le champ électrique parallèle produit par le terme de gradient parallèle de la pression des électrons. La partition de l'énergie entre les ions et les électrons est discutée à l'aide du calcul du terme de contrainte de pression. A partir des simulations cinétiques réalisées avec ou sans ions froids et avec ou sans champ guide, il est montré que la présence des ions froids renforce le gradient de pression des électrons réduisant le champ électrique normal et augmentant la vitesse de déplacement de la région de reconnexion. L'ensemble de ces effets modifie les échanges d'énergie et de plasma entre le vent solaire et la magnétosphère terrestre
Influence des aberrations optiques sur l'exactitude d'un gravimètre atomique
No full textInternational audienceWe present numerical simulations of the impact of laser beam wavefront aberrations in cold atom interferometers. We demonstrate that to reach accuracy at the mrad level, simulations cannot be based on a description of the retroreflection optics only with low-order Zernike polynomials, as the results will then depend on the decomposition order and the decomposition technique chosen. Moreover, simulations with high-order Zernike polynomials or equivalently high spatial frequency components require the propagation of aberrations to be taken into account, rather than adding them to the ideally propagated beam. Finally, we examine the impact of the parameters of the atomic source and show that the use of delta-kicked atomic cloud would efficiently mitigate the impact of this systematic effect