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In-situ globular clusters in alternative dark matter Milky Way galaxies: a first approach to fuzzy and core-like dark matter theories
No full textInternational audienceWe present a first analysis of the dynamics of in-situ globular clusters (GCs) in Milky Way (MW)-like galaxies embedded in fuzzy dark matter (FDM) halos, combining cosmological assembly histories from the TNG50 simulation with dedicated orbital integrations and analytical models. GC populations are initialized with identical distributions in normalized - in matched CDM and FDM halos. In a universe dominated by FDM, we identify three distinct regimes for the in-situ GC population depending on the particle mass . For , the dark matter becomes both compact and globally dominant, generating a deeper and more extended gravitational potential that supports a wider range of stable GC orbits, resulting in more massive and spatially extended GC systems. Finally, we extend our framework to make predictions for GC populations in alternative DM models, including warm dark matter and self-interacting dark matter, in both MW-like and dwarf galaxies. Our findings demonstrate that in-situ GC systems offer a sensitive and independent probe of the underlying DM physics, opening new avenues for observational constraints with upcoming Euclid
Multiwavelength observations of a new black-widow millisecond pulsar PSR J1544-2555
No full textInternational audienceWe report the discovery of a new black-widow millisecond pulsar, PSR J1544-2555, associated with the Fermi-LAT source 4FGL J1544.2-2554. Optical, radio, and gamma-ray observations confirmed its nature as a compact spider binary system. Optical photometry from ULTRACAM revealed a ~2.7-hour orbital period, guiding MeerKAT observations that detected ~2.4-ms radio pulsations. Subsequent timing campaigns using the Murriyang Parkes Telescope, the Effelsberg 100-m Radio Telescope, and the Nançay Radio Telescope allowed us to obtain a preliminary timing solution, which enabled us to find gamma-ray pulsations. The final timing solution, spanning 16 years of Fermi-LAT gamma-ray data, also displays orbital period variations typical of spider pulsars. X-ray observations from eROSITA indicate non-thermal emission, but the relatively low count rate prohibits the search for X-ray pulsations. Optical light curve modelling using Icarus suggests the asymmetry is best explained by a spot model, where uneven heating creates localised temperature variations on the companion. While the optical spectra we obtained are compatible with the physical properties we infer for the companion star, they were not of sufficient signal-to-noise to allow for radial velocity measurements, thus limiting constraints on the neutron star's mass. The observed bluer colour near the light curve minimum suggests possible non-thermal emission from intra-binary shocks, supported by the presence of an X-ray source. This discovery exemplifies the proven capability of the Fermi-LAT catalogue in identifying millisecond pulsar candidates and highlights the role of optical surveys in detecting variable sources suitable for radio follow-up
Particle acceleration up to the synchrotron burn-off limit in relativistic magnetized turbulence
No full textInternational audienceIn high-energy astrophysics, interpreting observed spectra hinges on understanding the competition between energy gains and radiative losses. To progress along these lines, we report on particle-in-cell simulations of particle acceleration in relativistic, magnetized turbulent pair plasmas including synchrotron radiative losses. Our key finding is that the particle energy spectrum does not terminate at this maximal energy but extends beyond with a steepened spectrum, up to the synchrotron burn-off limit where particles cool within a gyrotime. For our adopted parameters (magnetization and amplitude ), the particle distribution follows with below the predicted maximal energy, then steepens to above. The particle distribution and the radiated synchrotron spectra display strong variability near the cutoff energy down to timescales well below the largest eddy turn-around time. We substantiate our results by demonstrating that the acceleration rate itself displays a broken powerlaw-like distribution whose maximal value is the gyrofrequency. The highest energy particles are accelerated by a generalized Fermi process in ideal electric fields, driven by a gradient of the --velocity field of the magnetic field lines of relativistic amplitude, , ordered on a scale comparable to the particle gyroradius. We contend that this is a generic feature of relativistic, large-amplitude turbulence. Lastly, we apply our results to the Crab nebula, which exhibits a hierarchy of characteristic Lorentz factors similar to that studied here. We conclude that stochastic acceleration in this environment is a promising mechanism for explaining the highest-energy part of the synchrotron spectral energy distribution, and its variability. [Abridged
Uncooled pyroelectric a-YBCO detectors in the NIR to the MIR range: performance enhancement induced by calcium doping
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Joint statistical modeling and deep learning for exoplanet detection and characterization by direct imaging at high contrast
No full textInternational audienceThe detection of exoplanets, the characterization of their atmospheres, and the study of exoplanet formation mechanisms are major current challenges in astrophysics. High-contrast direct imaging (HCI) is one of the observational techniques of choice to address these questions. However, such observations are particularly demanding due to the extreme contrast levels and angular resolution required. In addition to the use of extreme adaptive optics and coronagraphs, advances in data science have become critical for analyzing these observations and disentangling the signals of interest (exoplanets and circumstellar disks) from the strong nuisance component (speckles and noise) that corrupts the data.In this context, we will present our recent developments in deep learning applied to HCI, aimed at the optimal and reliable extraction of astrophysical information from multivariate observations (including spatial, temporal, spectral, and multi-epoch diversity). These approaches are based on a fine modeling of the different components contributing to the total signal and incorporate physical domain knowledge as prior information. Emphasis will be placed on (i) combining deep learning models with statistical modeling of the nuisance, (ii) leveraging large archival datasets as a valuable source of diversity for tackling the unmixing task, and (iii) jointly exploiting the spectral diversity of observations.Our methods are tailored to the specific challenges of high-contrast imaging: (i) very low signal-to-noise ratios and non-stationary noise, (ii) detection of rare events, and (iii) absence of ground truth. Using data from the VLT/SPHERE instrument, we will show that these approaches enable fine modeling and effective subtraction of the nuisance component, leading to reliable and nearly optimal estimates of the astrophysical quantities of interest. This results in significantly improved detection sensitivity and more accurate astro-photometric characterization. The proposed approaches are also scalable and readily applicable to large-scale surveys.Looking ahead, instruments on the next generation of thirty-meter-class telescopes will enable the exploration of the innermost environments of Sun-like stars at unprecedented contrast levels. Achieving the associated scientific goals will require addressing several data science challenges: (i) approaching the ultimate performance limits of the instruments through optimal signal extraction, (ii) capturing complex, spatially structured nuisance exhibiting strong variability, and (iii) building robust nuisance models that go beyond the limitations of angular differential imaging, particularly in the vicinity of the host star. We will discuss these challenges in light of the methodological developments presented
<i>Euclid</i>: the potential of slitless infrared spectroscopy: a <i>z</i> = 5.4 quasar and new ultracool dwarfs
No full textInternational audienceWe demonstrate the potential of Euclid ’s slitless spectroscopy to discover high-redshift (z > 5) quasars and their mainphotometric contaminant, ultracool dwarfs. Sensitive infrared spectroscopy from space is able to efficiently identify bothpopulations, as demonstrated by Euclid Near-Infrared Spectrometer and Photometer Red Grism (NISP RGE ) spectra of thenewly discovered z = 5.404 quasar EUCL J181530.01+652054.0, as well as several ultracool dwarfs in the Euclid Deep FieldNorth and the Euclid Early Release Observation field Abell 2764. The ultracool dwarfs were identified by cross-correlatingtheir spectra with templates. The quasar was identified by its strong and broad C III ] and Mg II emission lines in the NISPRGE 1206–1892 nm spectrum, and confirmed through optical spectroscopy from the Large Binocular Telescope. The NISPBlue Grism (NISP BGE ) 926–1366 nm spectrum confirms C IV and C III ] emission. NISP RGE can find bright quasars atz ≈ 5.5 and z 7, redshift ranges that are challenging for photometric selection due to contamination from ultracool dwarfs.EUCL J181530.01+652054.0 is a high-excitation, broad absorption line quasar detected at 144 MHz by the LOw-FrequencyArray (L144 = 4.0 × 1025 W Hz−1 ). The quasar has a bolometric luminosity of 3 × 1012 L and is powered by a 3.4 × 109 Mblack hole. The discovery of this bright quasar is noteworthy as fewer than one such object was expected in the ≈20 deg2 surveyed.This finding highlights the potential and effectiveness of NISP spectroscopy in identifying rare, luminous high-redshift quasars,previewing the census of these sources that Euclid’s slitless spectroscopy will deliver over about 14 000 deg2 of the sk
Velocity fields and turbulence from cosmic filaments to galaxy clusters
No full textInternational audienceGalaxy clusters are currently the endpoint of the hierarchical structure formation; they form via the accretion of dark matter and cosmic gas from their local environment. In particular, filaments contribute grandly by accreting gas from cosmic matter sheets and underdense regions and feeding it to the galaxy clusters. Along the way, the gas in filaments is shocked and heated, which, together with the velocity structure within the filament, induces swirling and, thus, turbulence. In this work, we study a constrained hydrodynamical simulation replica of the Virgo cluster to characterise the velocity field in the two cosmic filaments connected to the cluster with unprecedented high resolution. First, we conduct a qualitative examination of slices extracted from the simulation. We study the temperature, the velocity field, and derived quantities in longitudinal cuts to study the general structure of the filaments and in transverse cuts to study their inner organisation and connection to cosmic matter sheets and underdense regions. Then, we conduct a quantitative study of velocities in Virgo's filaments by computing the 2D energy spectrum from 1 and 5~Mpc square maps extracted from the slices and centred on the core of the filaments. We show that the velocity field goes from mostly compressive far in the filaments to mostly solenoidal in Virgo's core. Moreover, we observe that the total energy spectrum in the filaments gains in amplitude and steepens towards Virgo
Cold Atom Quantum Inertial Sensors: a focus on geoscience applications
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