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A multi-omics dissection of the molecular mechanisms underlying water soaking in fresh-cut watermelon
No full textThe Milky Way in context: the formation of galactic discs and chemical sequences from a cosmological perspective
No full textWe study the formation of chemical sequences in stellar discs of Milky Way (MW)-mass galaxies in a full cosmological context with the AURIGA simulations, with implications for both the MW and external galaxies like M31. The analysis focuses on the conditions giving rise to bimodal alpha-chemistry and the potential influence of mergers (e.g. Gaia-Enceladus, GSE). We find a wide diversity of chemical sequences, without correlation between the emergence of dichotomous alpha-chemistry and GSE-like mergers. The transition between multiple alpha-sequences is sequential, and is mediated by modulations in the star formation rate (SFR). In some cases, this can be caused by the starburst and subsequent quiescence induced by mergers. In others, by exhaustion or violent disruption of the gas disc. Realizations with singular sequences either lack significant modulations in their SFR, or form too late to have a significant high-alpha sequence. The metallicity overlap between the high-and low-alpha sequences (as seen in the Solar neighbourhood of the MW) arises from accretion of metal-poor gas from the circumgalactic medium. This depends on gas disc thickness, with thinner discs losing their metal-poor extremities. Gas donation from singular gas-rich merger events are incapable of driving long-lived metal dilution (Delta[Fe / H] greater than or similar to 0 . 3), and we rule-out this scenario for the low-alpha sequence in the MW. Finally, the shape of alpha-sequences in the [Fe/H] versus [Mg/Fe] plane is related to long-term SFR trends, with a downward slanted locus (as observed in the low-alpha sequence of the MW) owing to a sustained or declining SFR
Multi-cloud crushing - the collective survival of cold clouds in galactic outflows
No full textThe ram-pressure acceleration of cold gas by hot outflows plays a crucial role in the dynamics of multiphase galactic winds. Recent numerical studies incorporating radiative cooling have identified a size threshold for idealized cold clouds to survive within high-velocity outflows. This study extends the investigation to a more complex morphology of cold gas as observed in the interstellar medium. We conduct 3D hydrodynamic simulations of ensembles of individual spherical similar to 10(4 )K clouds to systematically explore under which conditions the cold clouds can survive. We find that cloud ensembles can survive collectively - even when individual clouds, if isolated, would be rapidly destroyed. Our results indicate that, besides the morphology, factors such as tight packing, small intercloud distance, and higher fragmentation facilitate survival. We propose a novel multi-cloud survival criterion that accounts for collective properties of the cloud system, including total gas mass and the geometric configuration based on an effective volume filling fraction of the cold gas F-V. This fraction is computed by constructing a composite volume from individual enclosing conical boxes aligned with the wind, incorporating spatial overlap, and cloud-tail spreading. The box dimensions scale with the critical survival radius r(crit) from the single-cloud criterion. We find a threshold F-V,F-crit approximate to 0.24 among our simulations that robustly separates surviving from destroyed systems across diverse geometric configurations. Our findings emphasize the critical importance of initial cloud distribution and fragmentation in governing the long-term evolution and survival of cold gas structures, providing insight into observed multiphase outflows and circumgalactic medium dynamics
The thesan project: public data release of radiation-hydrodynamic simulations matching reionization-era JWST observations (Vol 530, pg 3765, 2024)
No full textChronology of our Galaxy from Gaia colour-magnitude diagram fitting (ChronoGal) IV. The inner Milky Way stellar age distribution
No full textThe Milky Way's inner region is dominated by a stellar bar and a boxy-peanut-shaped bulge. However, which stellar populations inhabit the inner Galaxy or how star formation proceeded there is still unknown. The difficulty in studying these stars stems from their location in dense regions that are strongly impacted by extinction and crowding effects. In this work we used star formation histories computed in the solar neighbourhood via Gaia colour-magnitude diagram fitting to shed light on the evolution of the central regions of our Galaxy. For that, we obtained precise age distributions for the non-negligible amount of super-metal-rich stars ([M/H] similar to 0.5) in the solar neighbourhood (more than 5% of the total stars within 400 pc of the plane). Assuming that these stars were born in the inner Galaxy and migrated outwards, those distributions should be indicative of the true stellar age distribution in the inner Galaxy. Surprisingly, we find that these age distributions are not continuous but show clear signs of episodic star formation (similar to 13.5, 10.0, 7.0, 4.0, 2.0, and less than 1 Gyr ago). Interestingly, with the exception of the 4 Gyr event, the timings of the detected events coincide with the formation of the primitive Milky Way and with known merging events or satellite encounters (Gaia-Enceladus-Sausage, Sagittarius dwarf galaxy, and the Magellanic Clouds), suggesting that these events could have triggered global star-forming episodes. These results are compatible with a scenario in which Gaia-Enceladus-Sausage is responsible for the formation of the bar 10 Gyr ago. However, we cannot associate any accretion counterpart with the event that occurred 4 Gyr ago, leaving open the possibility of a late formation of the bar, as previously proposed. The Auriga Superstars simulations also indicate that metal-rich stars in the solar neighbourhood-like regions formed at discrete times and migrated from the inner parts of barred galaxies, suggesting a possible link to bar dynamics and satellite accretion. This novel analysis allows us to indirectly witness the evolution of the inner Milky Way and constrain dynamical models of the Milky Way bar
Validating a non-local stellar convection model with 3D hydrodynamics simulations
No full textContext. The efficient transport of energy and chemical elements by convective motions has a profound effect on the structure and evolution of stars. These motions occur on the relatively short dynamical timescale of convection and are intrinsically multi-dimensional. Stellar models usually rely on the one-dimensional mixing-length approximation of these processes, which is known to break down at convective boundaries. The Kuhfu ss, R. (1987, Dissertation, Technische Universit & auml;t M & uuml;nchen, M & uuml;nchen) convection model has been shown to handle convective boundaries in a more consistent way. Aims. We test the assumptions that enter the Kuhfu ss model using multi-dimensional hydrodynamics simulations, and we compare the results with existing one-dimensional models. Where possible, we also aim to calibrate the parameters of the Kuhfu ss model using the simulations. Methods. We computed one-dimensional stellar models employing the Kuhfu ss model of a 3 M-circle dot main-sequence star. These models were compared to three-dimensional hydrodynamic simulations obtained with the code called SEVEN-LEAGUE HYDRO and using the Reynolds-averaged Navier Stokes analysis. We analysed the global convective variables and individual contributions to the equations of the convection model. Results. The turbulent kinetic energy as predicted by the Kuhfu ss model agrees well with the simulation results. Towards the boundary of the convective core, the simulations show a layer of a positive entropy gradient that coincides with a positive convective flux, as predicted by the convection model. The terms involving pressure fluctuations are found to have a non-negligible magnitude. Conclusions. The agreement of the turbulent kinetic energy equation for the convection model and the simulation is an important sign that the convection model is physically accurate. The gradient of the mean entropy that we found in the multi-dimensional simulations and in the Kuhfu ss model confirms the existence of a Deardorff layer, that is, of a layer with a subadiabtic temperature stratification and positive convective flux. This is not predicted by the mixing-length theory. The assumption that turbulence is isotropic and that pressure fluctuations are negligible needs to be revisited in the convection model
Probing the millisecond pulsar origin of the γ-ray excess in the Galactic centre with LISA
No full textThe gigaelectronvolt gamma-ray excess observed towards the Galactic centre remains unexplained. While dark matter annihilation has long been considered a leading explanation, an alternative scenario involving a large population of millisecond pulsars remains viable. Testing this hypothesis with electromagnetic observations is difficult, as pulsar searches in the bulge are strongly affected by interstellar scattering, high sky temperature, and source confusion. We investigate whether gravitational-wave observations with the Laser Interferometer Space Antenna (LISA) could provide an independent probe of the millisecond pulsar binary population in the Galactic bulge in the future. We constructed synthetic populations of detached millisecond pulsar-white dwarf binaries under two illustrative formation scenarios: an accreted scenario, in which systems are deposited by disrupted globular clusters, and an in situ scenario, in which binaries form through isolated binary evolution. In both cases, only 10(-5)-10(-4) of the underlying bulge population is detectable by LISA. Still, even a few detections would imply tens to hundreds of thousands of unseen systems. Accreted binaries are expected to have lower chirp masses (similar to 0.4 M-circle dot), while in situ binaries produce more massive companions (similar to 0.9 M-circle dot), though part of this contrast reflects our modelling assumptions. LISA will measure binary frequencies with high precision, but chirp masses can only be determined for the most massive or highest-frequency systems. Thus, identifying millisecond-pulsar binaries among the far more numerous double white dwarfs will be challenging, as their gravitational-wave signals alone are indistinguishable. However, coordinated follow-up with the Square Kilometre Array of LISA-selected targets could directly test the millisecond-pulsar explanation of the gamma-ray excess
GAP vs. MACE: efficiency evaluation in a liquid electrolyte system
No full textMachine learning interatomic potentials (MLIPs) have revolutionized molecular simulations, but as they evolve, so does the demand for advanced computing architectures, particularly graphics processing units (GPUs). However, the high cost of GPUs limits accessibility, making it crucial to compare GPU and central processing unit (CPU) based MLIPs under practical conditions. This study examines two popular MLIPs: the GPU-accelerated multi-atomic cluster expansion model and the CPU-based Gaussian approximation potentials model, applied to a battery electrolyte system known for its complex properties. By focusing on these models, our study evaluates differences in computational performance, resource efficiency, and accuracy in reproducing experimental properties. This rigorous benchmark provides insights into the trade-offs between GPU and CPU-based approaches in molecular simulations
Probing Instantaneous Single-Molecule Chirality in the Planar Ground State of Formic Acid
No full textWe experimentally demonstrate that individual molecules of formic acid are chiral even when they are in the vibronic ground state, which has a planar equilibrium structure. We ionize the C 1 s shell of the molecule and record the photoelectron in coincidence with positively charged fragments. This provides two consecutive measurements of the structure of one molecule, the first by photoelectron diffraction imaging and the second by Coulomb explosion imaging. We find that both measurements show the same handedness of the specific molecule. The phenomenon of being achiral on average but chiral at the level of individual molecules is general to prochiral molecules and is a consequence of the three-dimensional zero-point delocalization of the nuclei in the vibrational ground state
