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Evidence of haze control of Pluto’s atmospheric heat balance from JWST/MIRI thermal light curves
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The odd primordial halo of the Milky Way implied by Gaia. A shallow core, but a steep decline
No full textInternational audiencePrimordial dark matter halos are well understood from cold dark matter-only simulations. Since they can contract significantly as baryons settle into their centers, direct comparisons with observed galaxies are complicated. We present an approach to reversing the halo contraction by numerically calculating the halo response to baryonic infall and iterating the initial condition. This allowed us to derive spherically averaged primordial dark matter halos for observed galaxies. We applied this approach to the Milky Way and found that the latest Gaia measurements for the rotation velocities imply an odd primordial Galactic halo: Its concentration and total mass differ by more than 3 from the predictions, and the density profile presents an inner core that is too shallow and an outer decline that is too steep to be compatible with the cold dark matter paradigm
Euclid Quick Data Release (Q1): Identification of massive galaxy candidates at the end of the Epoch of Reionisation
No full textInternational audienceProbing the presence and properties of massive galaxies at high redshift is one of the most critical tests for galaxy formation models. In this work, we search for galaxies with stellar masses M* > 10^10.25 Msun at z in [5,7], i.e., towards the end of the Epoch of Reionisation, over a total of ~23 deg^2 in two of the Euclid Quick Data Release (Q1) fields: the Euclid Deep Field North and Fornax (EDF-N and EDF-F). In addition to the Euclid photometry, we incorporate Spitzer Infrared Camera (IRAC) and ground-based optical data to perform spectral energy distribution (SED) fitting, obtaining photometric redshifts and derived physical parameters. After applying rigorous selection criteria, we identify a conservative sample of 145 candidate massive galaxies with M* > 10^10.25 Msun at z in [5,7], including 5 objects with M* > 10^11 Msun. This makes for a surface density of about 6.3 deg^-2 at z in [5,7], which should be considered a lower limit because of the current depth of the Euclid data (H_E < 24, 5 sigma in Q1). We find that the inferred stellar masses are consistent with galaxy formation models with standard star-formation efficiencies. These massive galaxies have colour excess E(B-V) values up to 0.75, indicating significant dust attenuation in some of them. In addition, half of the massive galaxies have best-fit ages comparable to the age of the Universe at those redshifts, which suggests that their progenitors were formed very early in cosmic time. About 78% of the massive galaxies lie on the star-forming main sequence (MS) in the SFR-M* plane, ~12% are found in the starburst region, and 10% in the transition zone between the MS and starbursts. We find no significant evidence for outshining or AGN contamination that could account for the elevated specific star-formation rates (sSFR) observed in the ~12% of galaxies classified as starbursts
Unlocking the mystery of strontium synthesis in the early Galaxy through analysis of barium isotopes in very metal-poor stars
No full textInternational audienceAims . We determine the contributions of the rapid (r) and slow (s) neutron capture processes to the Ba isotope mixture, along with Ba, Eu, and Sr NLTE abundances, in a sample of very metal-poor stars. The selected stars formed before the contribution from the main s-process in low- and intermediate-mass stars became significant. Some of our sample stars are enhanced in Sr, with [Sr/Ba] reaching up to 0.7. These stars gained their high Sr abundance from a poorly understood process, sometimes referred to in the literature as a light element primary process, which may appear to be a weak s-process or a weak r-process. Our aim is to uncover the nature of this additional Sr source. Methods . The abundances derived from the resonance Ba II 4554 and 4934 Å lines are influenced by the adopted Ba isotope mixture. We computed Ba isotope mixtures corresponding to different r- to s-process contributions (pure r-process, 80%/20%, 50%/50% and 12%/88%, i.e. solar ratio) and determined the corresponding abundances from the Ba II resonance lines in each sample star. Additionally, we determined Ba abundances from weak subordinate Ba II lines, which are unaffected by the adopted Ba isotope mixture. We then compared the Ba abundances derived from the subordinate lines with those from the Ba II resonance lines. Results . We find a higher s-process contribution to Ba isotopes in stars with greater [Sr/Eu] and [Sr/Ba] overabundances, suggesting that the additional Sr synthesis was due to the early s-process occurring in massive stars. Using Sr-enhanced stars, we estimate the [Sr/Ba] ratio produced by the early s-process and obtain [Sr/Ba] earlyS = 1.1 ± 0.2. The derived value should be regarded as an upper limit, as we cannot definitively exclude the possibility of a contribution to Sr from the weak r-process, which produces Sr but not Ba. Regarding the potential synthesis of Sr and Ba in the i-process in massive stars, our results for Ba isotopes and element abundances argue that there was no detectable contribution from this process within the error bars in our sample stars. Conclusions . In the early Galaxy, before significant main s-process enrichment, barium and strontium were produced primarily by the main r-process and the early s-process, which occurred in rapidly rotating massive stars
Modélisation du Bruit Newtonien affectant le détecteur d'ondes gravitationnelles Virgo
No full textVibro-acoustique : session générale; GVB - Vibro acoustique et Contrôle du BruitNational audienceAvec ∼100 détections réalisées par le réseau LIGO-Virgo-KAGRA au cours des 10 dernières années, l'observation gravitationnelle occupe aujourd'hui une place importante en astrophysique. Le détecteur Virgo est un interféromètre de Michelson modifié avec deux bras de 3 km chacun contenant des résonateurs optiques de Fabry- Perot permettant d'atteindre des puissances laser de 150 kW. Sa sensibilité élevée le rend capable de mesurer une déformation relative d'espace d'origine gravitationnelle (∆L/L) de l'ordre de ∼10^-21. A cette échelle, les capacités de détections sont limitées par de nombreuses sources de bruits fondamentaux. Parmi celles-ci, le bruit « newtonien » ou « gradient de gravité » (sismique et atmosphérique/acoustique) pourrait limiter la sensibilité à basse fréquence (en dessous d'une dizaine de Hertz) de Virgo lorsqu'il atteindra sa pleine capacité de détection ainsi que celle des détecteurs de la prochaine génération tels que le télescope Einstein et le Cosmic Explorer américain. Cet article se concentre sur la modélisation du bruit newtonien d'origine acoustique, c'est-à-dire les petites fluctuations du champ de gravité résultant du champ acoustique présent dans les salles d'expérimentation. Le champ gravitationnel fluctuant influe directement sur les éléments optiques sensibles, tels que les miroirs de l'interféromètre. Le bruit induit est quantifié à l'aide modèle acoustique numérique de la salle expérimentale lorsqu'elle est excitée par le système de climatisation
Optimized squeezing for accurate differential sensing under large phase noise
No full textInternational audienceAtom interferometers are reaching sensitivities fundamentally constrained by quantum fluctuations. A main challenge is to integrate entanglement into quantum sensing protocols to enhance precision while ensuring robustness against noise and systematics. Here, we theoretically investigate differential phase measurements with two atom interferometers using spin-squeezed states of N atoms, accounting for common-mode phase noise spanning the full 2 π range. We estimate the differential signal using model-free ellipse fitting, a robust method requiring no device calibration and resilient to additional noise sources. Our results show that spin-squeezing enables sensitivities below the standard quantum limit (SQL). Specifically, we identify optimal squeezed states that minimize the differential phase uncertainty, scaling as N − 2 / 3 , thus overcoming the SQL by a factor N 1 / 6 , while eliminating the bias inherent in ellipse fitting methods. We benchmark our protocol against the Cramér–Rao bound and compare it with hybrid methods that incorporate auxiliary classical sensors. Our findings provide a pathway to robust and high-precision atom interferometry, in realistic noisy environments and using readily available states and estimation methods
SIEGE IV: compact star clusters in cosmological simulations with high star formation efficiency and sub-parsec resolution
No full textInternational audienceThe formation of compact high-redshift star-forming clumps, the physical processes driving their evolution and their potential connection to present-day Globular Clusters are key open questions in galaxy formation. In this work, we aim to shed light on these aspects using the SImulating the Environment where Globular clusters Emerged (SIEGE) project, a suite of cosmological zoom-in simulations with sub-parsec resolution specifically designed to investigate the physical conditions behind the origin of compact stellar systems in high-redshift environments. The simulation object of this study focuses on a dwarf galaxy with a virial mass of a few 10 9 M ⊙ at z = 6.14, where the spatial resolution reaches 0.3 pc h -1 . Individual stars are formed directly by sampling the initial mass function with a 100% star formation efficiency, a setup designed to explore the impact of a high star formation efficiency under highredshift conditions. The simulation reveals the emergence of numerous stellar clumps with sizes of 1-3 pc, stellar surface densities up to almost 10 4 M ⊙ pc -2 , and masses predominantly spanning from 10 3 M ⊙ to several 10 4 M ⊙ , with a few reaching 10 5 M ⊙ and up to 10 6 M ⊙ . All clumps form during intense, short bursts of star formation lasting less than a Myr, without noticeable signs of second peaks of star formation or accretion, often with negligible dark matter content (dark-to-stellar mass ratios below 1 within three times their effective radii). We measure a clear correlation between mass and size, and a clump mass function described by a power-law with a slope of -2. Star formation conditions in the simulation behave similarly to those of a feedback-free starburst scenario, where dense clumps form due to inefficient stellar feedback over small timescales. Notably, some clumps exhibit properties closely resembling those of present-day globular clusters, highlighting their potential evolutionary connection.</div
Coherent differential imaging of high-contrast extended sources with VLT/SPHERE ⋆
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Origin of gas in the Magellanic Bridge: MeerKAT detection of H I 21 cm absorption
No full textInternational audienceAims. H I 21 cm absorption lines are investigated to determine the origin of the neutral atomic hydrogen (H I ) of the Magellanic Bridge (MB). Using MeerKat Absorption Line Survey (MALS) data, we report the detection of an H I absorption line at a peak signal-to-noise ratio (S/N) of 10 caused by MB gas observed against the radio source J033242.97-724904.5. In combination with earlier data obtained with the Australia Telescope Compact Array (ATCA), our new detected H I line enables the exploration of the MB atomic hydrogen gas across 4–6 kpc. Methods. We investigated the radial velocity profiles from the ATCA data and included new data from MALS in the analysis. Apart from the excitation conditions, we considered the radial velocity structure of the H I gas seen in emission and absorption. The gas-to-dust ratio was quantified to help identify whether the MB gas had originated from the SMC (Small Magellanic Cloud) or the LMC (Large Magellanic Cloud). Results. The H I absorption lines toward lines of sight separated by a few kiloparsecs consistently coincide with the densest and possibly the coolest gas at the lower radial-velocity limit of the corresponding H I emission profiles. The gas-to-dust ratio was found to be consistent with the MB gas originating in the LMC. The large-scale velocity distribution, as seen from the H I absorption features, favors the LMC-SMC direct collision scenario over the close fly-by scenario, which is also supported by results from recent numerical simulations
The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. III. Aperture Masking Interferometric Observations of the Star HIP 65426 at 3.8 <i>μ</i>m
No full textInternational audienceWe present aperture masking interferometry (AMI) observations of the star HIP 65426 at 3.8 μm, as part of the JWST Direct Imaging Early Release Science program, obtained using the Near Infrared Imager and Slitless Spectrograph instrument. This mode provides access to very small inner working angles (even separations slightly below the Michelson limit of 0.5λ/D for an interferometer), which are inaccessible with the classical inner working angles of the JWST coronagraphs. When combined with JWST's unprecedented infrared sensitivity, this mode has the potential to probe a new portion of parameter space across a wide array of astronomical observations. Using this mode, we are able to achieve a 5σ contrast of Δm F380M ∼ 7.62 ± 0.13 mag relative to the host star at separations 0 .07, and the contrast deteriorates steeply at separations 0 .07. However, we detect no additional companions interior to the known companion HIP 65426b (at separation ∼0 .82 or - + 87 au 31 108). Our observations thus rule out companions more massive than 10-12 M Jup at separations ∼10-20 au from HIP 65426, a region out of reach of ground-or space-based coronagraphic imaging. These observations confirm that the AMI mode on JWST is sensitive to planetary mass companions at close-in separations (0 .07), even for thousands of more distant stars 80 Millennium Nucleus on Young Exoplanets and their Moons (YEMS).</div