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On the Potential Galactic Origin of the Ultra-High-Energy Event KM3-230213A
No full textInternational audienceThe KM3NeT observatory detected the most energetic neutrino candidate ever observed, with an energy between 72 PeV and 2.6 EeV at the 90% confidence level. The observed neutrino is likely of cosmic origin. In this article, it is investigated if the neutrino could have been produced within the Milky Way. Considering the low fluxes of the Galactic diffuse emission at these energies, the lack of a nearby potential Galactic particle accelerator in the direction of the event and the difficulty to accelerate particles to such high energies in Galactic systems, we conclude that if the event is indeed cosmic, it is most likely of extragalactic origin
Titan's surface composition
No full textInternational audienceIn some respects, the surface of Titan is one of the most Earth-like places in the solar system. However, two properties distinguish the surface of Titan from that of Earth: temperature and chemistry. Titan's mean surface temperature is −180°C (∼90 K), and water-ice plays the role that igneous and other types of silicate rocks play in the Earth's crust. The top layer of Titan's surface is largely covered by sedimentary deposits, in the form of dark hydrocarbon grains in the equatorial dunes, and liquid methane and ethane in the several large lakes and seas near the poles. A rich organic atmospheric chemistry and active geological processes (erosion from methane rain and the wind, in addition to stream-like and lacustrine processes) led to a surface composition including both new atmospheric aerosol sediments and materials exposed from the underlying crust. Identification of the chemical composition of Titan's surface therefore provides information on both the raw materials and subsequent modification of the geologic features on Titan's surface. However, the surface chemical composition of Titan remains uncertain, even after 13 years of Cassini exploration (2004–17) and valuable data acquired in situ on Titan's surface by the Huygens probe. In particular, the question of whether and where water-ice (Titan's dominant crustal composition) is exposed on the surface is still outstanding. Thus, consensus has not yet been reached even on the basic composition of some of Titan's major geologic units. Nonetheless, progress has been made in identifying key solid hydrocarbons and nitriles precipitated from the atmosphere, as well as the liquid methane- and ethane-composition of Titan's lakes. In the future, enhanced techniques for the analysis of Cassini data, space telescopes such as the JWST, laboratory measurements, the Dragonfly mission, and potentially other future orbiting missions with higher spectral and spatial resolution in the near-IR, may help resolve these questions
Effects of secular growth and mergers on the evolution of metallicity gradients and azimuthal variations in a Milky Way-like galaxy
No full textInternational audienceWe analyzed the evolution of the radial profiles and the azimuthal variations of the stellar metallicities from the VINTERGATAN simulation of a Milky Way-like galaxy. We find that negative gradients exist as soon as the disk settles at high redshift, and are maintained throughout the long-term evolution of the galaxy, including during major merger events. The inside-out growth of the disk and an overall outward radial migration tend to flatten these gradients in time. Major merger events only have a moderate and shortlived imprint on the [Fe/H] distributions with almost no radial dependence. The reason lies in the timescale for enrichment in Fe being significantly longer than the duration of the starbursts episodes, themselves slower than dynamical mixing during typical interactions. It results in signatures of major mergers becoming undetectable in [Fe/H] only a few megayears after pericenter passages. We note that considering other tracers like the warm interstellar medium, or monitoring the evolution of the metallicity gradient as a single value instead of a radial full profile could lead to different interpretations; we warn against oversimplifying this complex problem.</div
SIEGE III: The formation of dense stellar clusters in sub-parsec resolution cosmological simulations with individual star feedback
No full textStar clusters stand at the crossroads between galaxies and single stars. Resolving the formation of star clusters in cosmological simulations represents an ambitious and challenging goal, since modelling their internal properties requires very high resolution. This paper is the third of a series within the SImulating the Environment where Globular clusters Emerged (SIEGE) project, where we conduct zoom-in cosmological simulations with sub-parsec resolution that include the feedback of individual stars, aimed to model the formation of star clusters in high-redshift proto-galaxies. We investigate the role of three fundamental quantities in shaping the intrinsic properties of star clusters, i. e., i) pre-supernova stellar feedback (continuous or instantaneous ejection of mass and energy through stellar winds); ii) star formation efficiency, defined as the fraction of gas converted into stars per freefall time, for which we test 2 different values (epsi_ff=0.1 and 1), and iii) stellar initial mass function (IMF, standard vs top-heavy). All our simulations are run down to z=10.5, which is sufficient for investigating some structural properties of the emerging clumps and clusters. [Abridged] The prescription for a continuous, low-intensity feedback, along with the adoption of epsi_ff=1, produces star clusters with maximum stellar density values up to 10^4 M_sun pc^(-2), in good agreement with the surface density-size relation observed in local young star clusters (YSCs). Therefore, a realistic stellar wind description and a high star formation effiency are the key ingredients that allow us to achieve realistic star clusters characterised by properties comparable to those of local YSCs. In contrast, the other models produce too diffuse clusters, in particular the one with a top-heavy IMF
KM3-230213A: An Ultra-High Energy Neutrino from a Year-Long Astrophysical Transient
No full textInternational audienceThe Km3NET collaboration has recently reported the detection of a neutrino event with energy in excess of 100 PeV. This detection is in 2.5-3 tension with the upper limit on the neutrino flux at this energy imposed by IceCube and the Pierre Auger Observatory, if the event is considered part of the diffuse all-sky neutrino flux. We explore an alternative possibility that the event originates from a flare of an isolated source. We show that the data of Km3NET, IceCube and the Pierre Auger Observatory are consistent with the possibility of a source flare of duration yr with muon neutrino flux F \approx 3\times 10^{-10}(1\mbox{ yr }/ T) erg cm s. Constraints on the neutrino spectrum indicate that the protons responsible for the neutrino emission have a very hard spectrum in the eV energy range, or otherwise that the neutrinos are produced by photohadronic interactions with infrared photons. The all-sky rate of similar neutrino flaring sources is constrained to be yr
Higher derivative holography and temperature dependence of QGP viscosities
No full textInternational audienceRecent Bayesian analyses of heavy ion collision data have established a non-trivial temperature dependence of the shear and bulk viscosity per entropy. Motivated by this, we consider higher derivative corrections to realistic, bottom-up holographic models of quark-gluon plasma based on five-dimensional Einstein-dilaton theories and determine the dilaton potentials in the higher derivative terms by matching the Bayesian analyses. A byproduct of our analysis is the bulk viscosity that follows from the holographic V-QCD theory. Higher derivative corrections when treated perturbatively lead to tension with existing data. We investigate possible resolutions
Transit-timing variations in the AU Mic system observed with CHEOPS
No full textInternational audienceContext. AU Mic is a very active M dwarf star with an edge-on debris disk and two known transiting sub-Neptunes with a possible third planetary companion. The two transiting planets exhibit significant transit-timing variations (TTVs) that are caused by the gravi tational interaction between the bodies in the system. Aims. Using photometrical observations taken with the CHaracterizing ExOPlanet Satellite (CHEOPS), we aim to constrain the plan etary radii, the orbital distances, and the periods of AU Mic b and c. Furthermore, our goal is to determine the superperiod of the TTVs for AU Mic b and to update the transit ephemeris for both planets. Additionally, based on the perceived TTVs, we study the possible presence of a third planet in the system. Methods. We conducted ultra-high precision photometric observations with CHEOPS in 2022 and 2023. We used Allesfitter to fit the planetary transits and to constrain the planetary and orbital parameters. We combined our new measurements with results from previous years to determine the periods and amplitudes of the TTVs. We applied dynamical modelling based on TTV measurements from the 2018–2023 period to reconstruct the perceived variations. Results. We found that the orbital distances and periods for AU Mic b and c agree with the results from previous works. However, the values for the planetary radii deviate slightly from previous values, which we attribute to the effect of spots on the stellar surface. AU Mic c showed very strong TTVs, with transits that occurred ∼80 minutes later in 2023 than in 2021. Through a dynamical analysis of the system, we found that the observed TTVs can be explained by a third planet with an orbital period of ∼12.6 days and a mass of 0.203‑0.024+0.022 M⊕. We explored the orbital geometry of the system and found that AU Mic c has a misaligned retrograde orbit. The limited number of AU Mic observations prevented us from determining the exact dynamical configuration and planetary parameters. Further monitoring of the system with CHEOPS might help to improve these results
CHEOPS observations confirm nodal precession in the WASP-33 system
No full textInternational audienceAims. We aim to observe the transits and occultations of WASP-33 b, which orbits a rapidly rotating δ Scuti pulsator, with the goal of measuring the orbital obliquity via the gravity-darkening effect, and constraining the geometric albedo via the occultation depth. Methods. We observed four transits and four occultations with CHEOPS, and employ a variety of techniques to remove the effects of the stellar pulsations from the light curves, as well as the usual CHEOPS systematic effects. We also performed a comprehensive analysis of low-resolution spectral and Gaia data to re-determine the stellar properties of WASP-33. Results. We measure an orbital obliquity 111.3‑0.7+0.2 degrees, which is consistent with previous measurements made via Doppler tomography. We also measure the planetary impact parameter, and confirm that this parameter is undergoing rapid secular evolution as a result of nodal precession of the planetary orbit. This precession allows us to determine the second-order fluid Love number of the star, which we find agrees well with the predictions of theoretical stellar models. We are unable to robustly measure a unique value of the occultation depth, and emphasise the need for long-baseline observations to better measure the pulsation periods
Surveying the Whirlpool at Arcseconds with NOEMA (SWAN): II. Survey design and observations
No full textInternational audienceWe present Surveying the Whirlpool at Arcseconds with NOEMA (SWAN), a high-resolution, high-sensitivity survey to map molecular lines in the 3 mm band in M51 (the Whirlpool galaxy). SWAN has obtained the largest high-sensitivity map (∼5 × 7 kpc2) of N2H+ emission at ∼cloud-scale resolution (3″ ∼ 125 pc) in an external galaxy to date. Here, we describe the observations and data reduction of ∼214 hours of interferometric data from the Northern Extended Millimetre Array (NOEMA) and ∼55 hours of tailored new observations with the 30m telescope of the Institut de radioastronomie millimétrique (IRAM), as well as the combination of these NOEMA and new IRAM-30m observations with ∼14 hours of archival IRAM-30m observations. We detect widespread emission from nine molecular transition lines. The J = 1 ‑ 0 transitions of the CO isotopologs 13CO and C18O are detected at high significance across the full observed field of view (FoV). HCN(1‑0), HNC(1‑0), HCO+(1‑0), and N2H+(1‑0) are detected in the center, molecular ring, and spiral arms of the galaxy, while the shock tracer HNCO(4‑3) and (5‑4) and PDR tracer C2H(1‑0) are detected in the central ∼1 kpc and molecular ring only. For most of the lines that we detect, average line ratios with respect to 12CO are increased by up to a factor of ∼3 in the central 1 kpc, where an active galactic nucleus and its low-inclination outflow are present, compared to the disk. Line ratios between CO isotopologs show less variation across the SWAN FoV. Across the full SWAN FoV, 13CO, C18O, HCN, HNC, HCO+ and N2H+ are 8±22, 29±76, 17±35, 37±510, 26±53 and 63±3810 times fainter than 12CO, respectively, in pixels where each line is significantly detected. Although we observe variations in line ratios between larger-scale environments like the center and disk of M51, the scatter within each environment also indicates the influence of smaller-scale processes. The ability to measure these effects is only possible thanks to the high resolution and high sensitivity of the SWAN dataset across multiple environments. This provides the sharpest view of these molecular transitions over the largest physical area ever captured in an external galaxy
First upper limits on the 21-cm signal power spectrum of neutral hydrogen at from the LOFAR 3C196 field
No full textInternational audienceThe redshifted 21-cm signal of neutral hydrogen from the Epoch of Reionization (EoR) can potentially be detected using low-frequency radio instruments such as the Low-Frequency Array (LOFAR). So far, LOFAR upper limits on the 21-cm signal power spectrum have been published using a single target field: the North Celestial Pole (NCP). In this work, we analyse and provide upper limits for the 3C196 field, observed by LOFAR, with a strong Jy source in the centre. This field offers advantages such as higher sensitivity due to zenith-crossing observations and reduced geostationary radio-frequency interference, but also poses challenges due to the presence of the bright central source. After constructing a wide-field sky model, we process a single 6-hour night of 3C196 observations using direction-independent and direction-dependent calibration, followed by a residual foreground subtraction with a machine learned Gaussian process regression (ML-GPR). A bias correction is necessary to account for signal suppression in the GPR step. Still, even after this correction, the upper limits are a factor of two lower than previous single-night NCP results, with a lowest upper limit of at and (with ). The results also reveal an excess power, different in behaviour from that observed in the NCP field, suggesting a potential residual foreground origin. In future work, the use of multiple nights of 3C196 observations combined with improvements to sky modelling and ML-GPR to avoid the need for bias correction should provide tighter constraints per unit observing time than the NCP