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Filaments connected to galaxy clusters are crucial environments to study the building up of cosmic structures as they funnel matter towards the clusters' deep gravitational potentials. Identifying gas in filaments is a challenge, due to their lower density contrast which produces faint signals. The best chance to detect these signals is therefore in the outskirts of galaxy clusters. We revisit the X-ray observation of the cluster Abell 2744 using statistical estimators of anisotropic matter distribution to identify filamentary patterns around it. We report for the first time the blind detection of filaments connected to a galaxy cluster from X-ray emission using a filament-finder technique and a multipole decomposition technique. We compare this result with filaments extracted from the distribution of spectroscopic galaxies, through which we demonstrate the robustness and reliability of our techniques in tracing a filamentary structure of 3 to 5 filaments connected to Abell 2744., Comment: 13 pages, 9 figures. Submitted to A&A

Metallicity offers a unique window into the baryonic history of the cosmos, being instrumental in probing evolutionary processes in galaxies between different cosmic environments. We aim to quantify the contribution of these environments to the scatter in the mass-metallicity relation (MZR) of galaxies. By analysing the galaxy distribution within the cosmic skeleton of the Horizon Run 5 cosmological hydrodynamical simulation at redshift $z = 0.625$, computed using a careful calibration of the T-ReX filament finder, we identify galaxies within three main environments: nodes, filaments and voids. We also classify galaxies based on the dynamical state of the clusters and the length of the filaments in which they reside. We find that the cosmic environment significantly contributes to the scatter in the MZR; in particular, both the gas metallicity and its average relative standard deviation increase when considering denser large-scale environments. The difference in the average metallicity between galaxies within relaxed and unrelaxed clusters is $\approx 0.1 \text{ dex}$, with both populations displaying positive residuals, $\delta Z_{g}$, from the averaged MZR. Moreover, the difference in metallicity between node and void galaxies accounts for $\approx 0.14 \, \text{dex}$ in the scatter of the MZR at stellar mass $M_{\star} \approx 10^{9.35}\,\text{M}_{\odot}$. Finally, both the average [O/Fe] in the gas and the galaxy gas fraction decrease when moving to higher large-scale densities in the simulation, suggesting that the cores of cosmic environments host, on average, older and more massive galaxies, whose enrichment is affected by a larger number of Type Ia Supernova events., Comment: 17 pages, 17 figures

We present the principle of virtual action as a foundation of continuum mechanics. Used mainly in relativity, the method has a useful application in classical mechanics and places the notion of action as the basic concept of dynamics. The principle is an extension of virtual work to space-time. It extends the efforts made by d'Alembert and Lagrange. Unlike the classical case of equilibrium, the principle of virtual action becomes a postulate for the formulation of models in dynamics. It allows to use a minimal set of clear conjectures and is extended to the case of media with dissipation; it can be used for more complex systems.

By dispersive models of fluid mechanics we are referring to the Euler-Lagrange equations for the constrained Hamilton action functional where the internal energy depends on high order derivatives of unknowns. The mass conservation law is considered as a constraint. The corresponding Euler-Lagrange equations include, in particular, the van der Waals--Korteweg model of capillary fluids, the model of fluids containing small gas bubbles and the model describing long free-surface gravity waves. We obtain new conservation laws generalizing the helicity conservation for classical barotropic fluids.

Multiple-cluster systems, superclusters, contain large numbers of galaxies assembled in clusters inter-connected by multi-scale filamentary networks. As such, superclusters are a smaller version of the cosmic web and can be considered as miniature universes. Superclusters also contain gas, hot in the clusters and warmer in the filaments. Thus, they are ideal laboratories to study the interplay between the galaxies and the gas. In this context, the Shapley supercluster (SSC) stands out since it hosts the highest number of galaxies in the local universe. In addition, it is detected in both X-rays and via the thermal Sunyaev-Zel'dovich (tSZ) effect, making it ideal for a multi-wavelength study. Applying for the first time a filament-finder based on graphs, T-REx, on a spectroscopic galaxy catalogue, we uncovered the 3D filamentary network in and around SSC. Simultaneously, we used a large sample of photometric galaxies with information on their star formation rates (SFR) in order to investigate the quenching of star formation in the SSC environments which we define with the gas distribution in the Planck tSZ map and the ROSAT X-ray map. We confirm filaments already observed in the distribution of galaxies of the SSC, and detect new ones. We observe the quenching of star formation as a function of the gas, and show a general trend of decreasing SFR where the tSZ and X-ray signals are the highest. Within these regions, we also observe a rapid decline of the number of star-forming galaxies, coinciding with an increasing number of transitioning and passive galaxies. Within the filaments, the fraction of passive galaxies is larger than outside filaments, irrespective of the gas pressure. Our results suggest the zone of influence of the SSC, in which galaxies are pre-processed and quenched, is well defined by the tSZ signal that combines the density and temperature of the environments., Comment: 16 pages, 13 figures, submitted to A&A

We present a study of the evolution of cosmic filaments across redshift with an emphasis on some important properties: filament lengths, growth rates, and radial profiles of galaxy densities. Following an observation-driven approach, we build cosmic filament catalogues at z=0,1,2,3, and 4 from the galaxy distributions of the large hydro-dynamical run of the MilleniumTNG project. We employ the extensively used DisPerSE cosmic web finder code, for which we provide a user-friendly guide, including the details of a physics-driven calibration procedure, with the hope of helping future users. We perform the first statistical measurements of the evolution of connectivity in a large-scale simulation, finding that the connectivity of cosmic nodes (defined as the number of filaments attached) globally decreases from early to late times. The study of cosmic filaments in proper coordinates reveals that filaments grow in length and radial extent, as expected from large-scale structures in an expanding Universe. But the most interesting results arise once the Hubble flow is factored out. We find remarkably stable comoving filament length functions and over-density profiles, showing only little evolution of the total population of filaments in the past ~12.25 Gyrs. However, by tracking the spatial evolution of individual structures, we demonstrate that filaments of different lengths actually follow different evolutionary paths. While short filaments preferentially contract, long filaments expand along their longitudinal direction with growth rates that are the highest in the early, matter-dominated Universe. Filament diversity at fixed redshift is also shown by the different (~$5 \sigma$) density values between the shortest and longest filaments. Our results hint that cosmic filaments can be used as additional probes for dark energy, but further theoretical work is still needed., Comment: 17 pages, accepted in Astronomy & Astrophysics

Traditional turbulence models are derived for single-phase flow. Extension of the family of two-equation turbulence models for two-phase flow is obtained via scaling the transport equations by the density. In the special case of two-phase flow with a sharp interface, jump conditions exist. Two types of jump conditions are found: (1) jump in the partial differential equation (PDE) physical quantities such as density and viscosity and (2) jump in the turbulence frequency. We first derive and clarify the jump in the equations. The jump in the turbulence frequency is proportional to the kinematic viscosity ratio, which is approximately $10$ in the case of air-water. Then a new field, the inverse turbulence area, is considered to model the turbulence effects instead of the turbulence frequency. For the system of air and water, the effect of the jump of the kinematic viscosity is always greater than the effect arising from the jump of velocity gradient. This approximation leads to the assumption of a continuous inverse turbulence area scale. Validation versus experimental measurements from the literature is then presented to demonstrate the improvement of the model. In particular, the wave breaking phenomenon is simulated in two conditions: spilling and plunging wave breakers. The proposed model shows its ability to predict the turbulence in the surf zone accurately. Finally, it explains the low values of the time-averaged turbulent kinetic energy in the surf zone which is caused by the increase of the turbulence frequency in the air.

Context. Whereas X-ray clusters are extensively used for cosmology, their idealistic modelling, through the hypotheses of spherical symmetry and hydrostatic equilibrium, are more and more being questioned. Along these lines, the soft X-ray emission detected in tens of clusters with ROSAT was found to be higher than what expected from the idealistic hot gas modelling, pointing to our incomplete understanding of these objects. Aims. Given that cluster environments are at the interface between the hot intra-cluster medium (ICM), warm circum-galactic medium (WCGM) and warm-hot intergalactic medium (WHIM), we aim to explore the relative soft X-ray emission of different gas phases in circum-cluster environments. Method. By using the most massive halos in IllustrisTNG at z=0, we have predicted the hydrodynamical properties of the gas from cluster centers to their outskirts (5 R200), and modelled their X-ray radiation for various plasma phases. Results. First, we found that the radial profile of temperature, density, metallicity and clumpiness of the ICM are in good agreement with recent X-ray observations of clusters. Secondly, we have developed a method to predict the radial profile of soft X-ray emission in different bands, the column density of ions and the X-ray absorption lines (O VIII, O VII, Ne IX, and Ne IX) of warm-hot gas inside and around clusters. Conclusion. The warm gas (in the form of both WCGM and WHIM gas) is a strong emitter in soft X-ray bands, and is qualitatively consistent with the observational measurements. Our results suggest that the cluster soft excess is induced by the thermal emission of warm gas in the circum-cluster environments., Comment: 20 pages, 16 figures, submitted to A&A, comments are welcome

Invariance theorems in analytical mechanics, such as Noether's theorem, can be adapted to continuum mechanics. For this purpose, it is useful to give a functional representation of the motion and to interpret the groups of invariance with respect to the space of reference associated with Lagrangian variables. A convenient method of calculus uses the Lie derivative. For instance, Kelvin theorems can be obtained by such a method.

The invariance theorems obtained in analytical mechanics and derived from Noether's theorems can be adapted to fluid mechanics. For this purpose, it is useful to give a functional representation of the fluid motion and to interpret the invariance group with respect to time in the quadri-dimensional reference space of Lagrangian variables. A powerful method of calculation uses Lie's derivative, and many invariance theorems and conservation laws can be obtained in fluid mechanics.

The Leidenfrost effect is a phenomenon in which a liquid, poured onto a surface significantly hotter than the liquid's boiling point, produces a layer of vapor that prevents the liquid from rapid evaporation. Rather than making physical contact, a drop of water levitates above the surface. The temperature above which the phenomenon occurs is called the Leidenfrost temperature. The reason for the existence of the Leidenfrost temperature, which is much higher than the boiling point of the liquid, is not fully understood and predicted. Here we prove that the Leidenfrost temperature corresponds to a bifurcation in the solutions of equations describing evaporation of a nonequilibrium liquid-vapor interface. For water, the theoretical values of obtained Leidenfrost temperature, and that of the liquid bulk which is smaller than the boiling point of liquid, fit the experimental results found in the literature.

About 2100 star-forming galaxy protocluster candidates at z=1-4 were identified at sub-mm wavelengths in the Planck all sky survey. Follow-up spectroscopic observations of a few candidates have confirmed the presence of actual galaxy overdensities with large star-formation rates. In this work, we use state-of-the-art hydrodynamical simulations to investigate whether the Planck high-z sub-mm sources are progenitors of massive clusters at z=0. To match the PHz sources with simulated halos, we select the most star-forming halos from z = 3 to z =1.3 in the TNG300 simulation. The total star formation rate (SFR) of the simulated protocluster candidates is computed from the SFR of all the galaxies within an aperture corresponding to the Planck beam size, including those along the line-of-sight. The simulations reproduce the Planck derived SFRs as the sum of both, the SFR of at least one of the most SF high-z halo, and the average contribution from SF sources along the line-of-sight. Focusing on the spectroscopically confirmed PHz protoclusters, we compare the observed properties of their galaxy members with those in the most SF simulated halos. We find a good agreement in the stellar mass and SFR distributions, and in the galaxy number counts, but the SFR-stellar mass relation of the simulated galaxies tends to be shifted to lower SFRs with respect to the observed one. Based on the estimated final masses of the simulated halos, we infer that between 63% and 72% of the Planck selected protoclusters will evolve into massive galaxy clusters at z=0. Despite contamination from star-forming galaxies along the line of sight, we confirm the efficiency of Planck to select star-forming protoclusters at Cosmic Noon with the simulations, and provide a new criterion for selecting the most massive cluster progenitors at high-z, using observables like the number of galaxy members and their SFR distribution., Comment: Accepted to A&A, 17 pages, 11 figures, comments are welcome

Matter distribution in the environment of galaxy clusters, from their cores to their connected cosmic filaments, must be in principle related to the underlying cluster physics and it evolutionary state. We aim to investigate how radial and azimuthal distribution of gas is affected by cluster environments, and how it can be related to cluster mass assembly history. Radial physical properties of gas (velocity, temperature, and density) is first analysed around 415 galaxy cluster environments from IllustrisTNG simulation at z = 0 (TNG300-1). Whereas hot plasma is virialised inside clusters (< R200), the dynamics of warm hot inter-galactic medium (WHIM) can be separated in two regimes: accumulating and slowly infalling gas at cluster peripheries and fast infalling motions outside clusters (> 1.5R200). The azimuthal distribution of dark matter (DM), hot and warm gas phases is secondly statistically probed by decomposing their 2-D distribution in harmonic space. Inside clusters, the azimuthal symmetries of DM and hot gas are well tracing cluster structural properties, such as their center offsets, substructure fractions and elliptical shapes. Beyond cluster virialised regions, we find that WHIM gas follows the azimuthal distribution of DM thus tracing cosmic filament patterns. Azimuthal symmetries of hot and warm gas distribution are finally shown to be imprints of cluster mass assembly history, strongly correlated with the formation time, mass accretion rate, and dynamical state of clusters. Azimuthal mode decomposition of 2-D gas distribution is a promising probe to assess the 3-D physical and dynamical cluster properties up to their connected cosmic filaments., Comment: Accepted to A&A, 16 pages, 9 figures, comments are welcome

Filaments and clusters of the cosmic web have an impact on the properties of galaxies, switching off their star-formation, contributing to the build-up of their stellar mass, and influencing the acquisition of their angular momentum. In this work we make use of the IllustrisTNG simulation, coupled with the DisPerSE cosmic web extraction algorithm, to test which is the galaxy property most affected by the cosmic web and, conversely, to assess the differential impact of the various cosmic web features on a given galaxy property. Our aim is to use this information to better understand galaxy evolution and to identify on which galaxy property future efforts should focus to detect the cosmic web from the galaxy distribution. We provide a comprehensive analysis of the relation between galaxy properties and cosmic web features. We also perform extensive tests in which we try to disentangle the effect of local overdensities of galaxies on their properties from the effect of the large scale structure environment. Our results show that star-formation is the quantity that shows the strongest variation with the distances from the cosmic web features, but it is also the one that shows the strongest relation to the local environment of galaxies. On the other hand, the direction of the angular momentum of galaxies is the property that shows the weakest trends with distance from cosmic web features, while also being more independent from the local environment of galaxies. We conclude that the direction of the angular momentum of galaxies and its use to improve our detection of the cosmic web features could be the focus of futures studies benefiting from larger statistical samples., Comment: Updated version to match the one accepted for publication in A&A

The impact of photodetector nonlinearity on dual-comb spectrometers is described and compared to that of Michelson-based Fourier transform spectrometers (FTS). The optical sampling occurring in the dual-comb approach, being the key difference with FTS, causes optical aliasing of the nonlinear spectral artifacts. Measured linear and nonlinear interferograms are presented to validate the model. Absorption lines of H$^{13}$CN are provided to understand the impact of nonlinearity on spectroscopic measurements., Comment: 5 pages, 8 figures

Sheet cavitation appears in many hydraulic applicationss and can lead to technical issues. Some fundamental outcomes such as the complex topology of 3-Dimensional cavitation pockets and their associated dynamics need to be carefully visited.In the present paper, the dynamics of partial cavitation developing in a 3-D Venturi geometry and the interaction with sidewalls are numerically investigated. The simulations are performed usinf a one-fluid compressible Reynolds-Averaged Navier-Stokes (RANS solver associated to a non-linear turbulence model and a void transport-equation model. A detailed analysis of this cavitating flow is carried out using innovative tools such as Spectral Proper Orthogonal Decompositions. Particular attenttion is paid in the study of 3-D effects by comparing numerical results obtained with sidewalls and periodic conditions. A three-dimensional dynamics of the sheet cavitation, unrelated to the presence of sidewalls, is identified and discussed.

Matter distribution around clusters is highly anisotropic from their being the nodes of the cosmic web. Clusters' shape and the number of filaments they are connected to, i.e., their connectivity, should reflect their level of anisotropic matter distribution and must be, in principle, related to their physical properties. We investigate the influence of the dynamical state and the formation history on both the morphology and local connectivity of about 2400 groups and clusters of galaxies from the large hydrodynamical simulation IllustrisTNG at z=0. We find that the mass of groups and clusters mainly influences the geometry of the matter distribution: massive halos are significantly more elliptical, and more connected to the cosmic web than low-mass ones. Beyond the mass-driven effect, ellipticity and connectivity are correlated and are imprints of the growth rate of groups and clusters. Both anisotropy measures appear to trace different dynamical states, such that unrelaxed groups and clusters are more elliptical and more connected than relaxed ones. This relation between matter anisotropies and dynamical state is the sign of different accretion histories. Relaxed groups and clusters are mostly formed long time ago, and slowly accreting matter at the present time. They are rather spherical and weakly connected to their environment, mostly because they had enough time to relax and, hence, lost the connection with their preferential directions of accretion and merging. In contrast, late-formed unrelaxed objects are highly anisotropic with large connectivities and ellipticities. These groups and clusters are in formation phase and must be strongly affected by the infalling of materials from filaments., Comment: Accepted to A&A, 13 pages, 11 figures, comments are welcome

In the quadri-dimensional space-time, the variation of Hamilton's action is a powerful tool to study the process equations for conservative fluid media. In this framework, Hamilton's principle allows to obtain equation of motions, equation of energy but also Rankine-Hugoniot conditions. The varia-tional method may be a versatile key to obtain the shock-wave conditions for complex media when the equations of processes are not expressed by linear or quasi-linear differential equations., Comment: Ricerche di matematica, Springer Verlag, 2020

Recent experiments conducted in the International Space Station highlight the apparent periodicity of leaf oscillations and other biological phenomena associated with rhythmic variations of lunisolar forces. These events are similar to those occurring on Earth, but with greater effects over a shorter period of time. Among the possible disturbances, other than forced or self-existing oscillations, parametric resonances appear caused by a small periodic term; such is the case of fluids subjected to small periodic variations in gravitational forces in microscopic or mesoscopic plant channels filled with sap and air-vapor. The interface instabilities verify a Mathieu's second order differential equation resulting from a Rayleigh-Taylor stability model. These instabilities appear during the Moon's rotation around the Earth and during the revolution of the International Space Station. They create impulses of pressure and sap movements in the network of roots, stems and leaves. The model can explain the effects of the lunar tide on plant growth. The eccentricity of the lunar orbit around the Earth creates an important difference between the apogee and perigee of the Moon's trajectory and therefore the tidal effects can depend on the distance between the Moon and the Earth.

By using the Hamilton principle of stationary action, we derive the governing equations and Rankine-Hugoniot conditions for continuous media where the specific energy depends on the space and time density derivatives. The governing system of equations is a time reversible dispersive system of conservation laws for the mass, momentum and energy. We obtain additional relations to the Rankine-Hugoniot conditions coming from the conservation laws and discuss the well-founded of shock wave discontinuities for dispersive systems.

We present a statistical study of the filamentary structures of the cosmic web in the large hydro-dynamical simulations Illustris-TNG, Illustris, and Magneticum at redshift z=0. We focus on the radial distribution of the galaxy density around filaments detected using the Discrete Persistent Structure Extractor (DisPerSE). We show that the average profile of filaments presents an excess of galaxy density (> 5 sigma) up to radial distances of 27 Mpc from the core. The relation between galaxy density and the length of filaments is further investigated showing that short (L_f < 9 Mpc) and long (L_f > 20 Mpc) filaments are two statistically different populations. Short filaments are puffier, denser, and more connected to massive objects, whereas long filaments are thinner, less dense, and more connected to less massive structures. These two populations trace different environments and may correspond to bridges of matter between over-dense structures (short filaments), and to cosmic filaments shaping the skeleton of the cosmic web (long filaments). Through Markov Chain Monte Carlo (MCMC) explorations, we find that the density profiles of both short and long filaments can be described by the same empirical models (generalised Navarro, Frenk and White, beta-model, a single and a double power law) with different and distinct sets of parameters., Comment: Accepted in A&A, 15 pages, 14 figures