G. Murante - Academia.edu (original) (raw)

Papers by G. Murante

We present an implementation of smoothed particle hydrodynamics (SPH) with improved accuracy for ... more We present an implementation of smoothed particle hydrodynamics (SPH) with improved accuracy for simulations of galaxies and the large-scale structure. In particular, we combine, implement, modify and test a vast majority of SPH improvement techniques in the latest instalment of the GADGET code. We use the Wendland kernel functions, a particle wake-up time-step limiting mechanism and a time-dependent scheme for artificial viscosity, which includes a high-order gradient computation and shear flow limiter. Additionally, we include a novel prescription for time-dependent artificial conduction, which corrects for gravitationally induced pressure gradients and largely improves the SPH performance in capturing the development of gas-dynamical instabilities. We extensively test our new implementation in a wide range of hydrodynamical standard tests including weak and strong shocks as well as shear flows, turbulent spectra, gas mixing, hydrostatic equilibria and self-gravitating gas clouds....

Cosmological simulations' output can be stored in an archive and ingested into a database. T... more Cosmological simulations' output can be stored in an archive and ingested into a database. Then can be connected to a web interface to allow the end user to explore it. This matches the VO idea of handling the data directly on the server side leaving the user only with the results of the query, or other end products, on his own machine. Besides data searching data centers are then requested to provide services to let the user preview and analyze data and metadata (both generated on-the-fly or pre-computed) with computing performed on the server side and letting only the results to be visualized on the user desktop (or sent to him). Here we present the IA2-ITVO (Italian Center for Astronomical Archives - Italian Theoretical Virtual Observatory) archive web interface mainly focusing on the 'Level 2' post-processing capabilities of the portal and its connection with other VO tools.

Monthly Notices of the Royal Astronomical Society, 2013

A large sample of cosmological hydrodynamical zoom-in simulations with Adaptive Mesh Refinement (... more A large sample of cosmological hydrodynamical zoom-in simulations with Adaptive Mesh Refinement (AMR) is analysed to study the properties of simulated Brightest Cluster Galaxies (BCGs). Following the formation and evolution of BCGs requires modeling an entire galaxy cluster, because the BCG properties are largely influenced by the state of the gas in the cluster and by interactions and mergers with satellites. BCG evolution is also deeply influenced by the presence of gas heating sources such as Active Galactic Nuclei (AGNs) that prevent catastrophic cooling of large amounts of gas. We show that AGN feedback is one of the most important mechanisms in shaping the properties of BCGs at low redshift by analysing our statistical sample of simulations with and without AGN feedback. When AGN feedback is included BCG masses, sizes, star formation rates and kinematic properties are closer to those of the observed systems. Some small discrepancies are observed only for the most massive BCGs, an effect that might be due to physical processes that are not included in our model.

Monthly Notices of the Royal Astronomical Society, 2011

We present results based on an implementation of the Godunov smoothed particle hydrodynamics (GSP... more We present results based on an implementation of the Godunov smoothed particle hydrodynamics (GSPH), originally developed by Inutsuka, in the GADGET-3 hydrodynamic code. We first review the derivation of the GSPH discretization of the equations of moment and energy conservation, starting from the convolution of these equations with the interpolating kernel. The two most important aspects of the numerical implementation of these equations are (a) the appearance of fluid velocity and pressure obtained from the solution of the Riemann problem between each pair of particles, and (b) the absence of an artificial viscosity term. We carry out three different controlled hydrodynamical three-dimensional tests, namely the Sod shock tube, the development of Kelvin-Helmholtz instabilities in a shear-flow test and the 'blob' test describing the evolution of a cold cloud moving against a hot wind.

Monthly Notices of the Royal Astronomical Society, 1997

We show that an arrangement of singular density concentrations accounts for the scaling exponents... more We show that an arrangement of singular density concentrations accounts for the scaling exponents observed in the luminous matter distribution in the Universe for scales below 10Mpc. This model provides a good description of the matter distribution on those smaller scales.

Monthly Notices of the Royal Astronomical Society, 2014

We investigate two modes of coupling the feedback energy from a central AGN to the neighbouring g... more We investigate two modes of coupling the feedback energy from a central AGN to the neighbouring gas in galaxy simulations: kinetic -velocity boost, and thermal -heating. We formulate kinetic feedback models for energy-driven wind (EDW) and momentum-driven wind (MDW), using two free parameters: feedback efficiency ǫ f , and AGN wind velocity v w . A novel numerical algorithm is implemented in the SPH code GADGET-3, to prevent the expansion of a hole in the gas distribution around the BH. We perform simulations of isolated evolution and merger of disk galaxies, of Milky-Way mass as well as lower and higher masses. We find that in the isolated galaxy BH kinetic feedback generates intermittent bipolar jet-like gas outflows. We infer that current prescriptions for BH subgrid physics in galaxy simulations can grow the BH to observed values even in an isolated disk galaxy. The BH growth is enhanced in a galaxy merger, which consequently requires different model parameters to fit the observations than an isolated case. Comparing the [M BH − σ ⋆ ] relation obtained in our simulations with observational data, we conclude that it is possible to find parameter sets for a fit in all the models (e.g. v w = 10000 km/s and ǫ f = 0.25 for BH kinetic EDW), except for the case with MDW feedback in a galaxy merger, in which the BH is always too massive. The BH thermal feedback implementation of within the multiphase star-formation model is found to have negligible impact on gas properties; and the effect claimed in all previous studies is attributed to gas depletion around the BH by the creation of an artificial hole. The BH mass accretion rate in our simulations exhibit heavy fluctuations. The star formation rate is quenched with feedback by removal of gas. The circumgalactic medium (CGM) gas at galactocentric distances (20 − 100)h −1 kpc are found to give the best metallicity observational diagnostic to distinguish between BH models.

Astroparticle Physics, 1996

We discuss the scaling analysis of CDM and CHDM simulations. We show that on scales larger than a... more We discuss the scaling analysis of CDM and CHDM simulations. We show that on scales larger than about 4-5 h-' Mpc the two models behave quite differently. In particular, CDM simulations with bias b = I .5 reveal a smooth transition from small-scale nonlinear clustering to homogeneity, while CDM models with bias b = 1 are characterised by the existence of an intermediate scaling regime with generalized dimensions between 2 and 3. The CHDM models tend to generate an intermediate scaling regime with values of the generalized dimensions smaller than 2. Correspondingly. the value of the tilling factor on intermediate scales. defined as the fraction of non-empty volumes sampling the distribution, is different for CDM and CHDM simulations: the CHDM model is less "space-filling" than the standard CDM. These results indicate that the scaling analysis is a valuable tool for distinguishing between different cosmological models and that a careful evaluation of the behavior of the galaxy distribution in the weakly nonlinear regime between about 5 and 20 h-' Mpc could provide hints about the reliability of different DM models.

Astronomy and Astrophysics, 2005

We perform a detailed analytical and numerical study of the dynamics of perturbations (vortex/ape... more We perform a detailed analytical and numerical study of the dynamics of perturbations (vortex/aperiodic mode, Rossby and spiral-density waves) in 2D compressible disks with a Keplerian law of rotation. We draw attention to the process of spiral-density wave generation from vortices, discussing, in particular, the initial, most peculiar stages of wave emission. We show that the linear phenomenon of wave generation by vortices in smooth (without inflection points) shear flows found by using the so-called non-modal approach, is directly applicable to the present case. After an analytical non-modal description of the physics and characteristics of the spiral-density wave generation/propagation in the local shearing-sheet model, we follow the process of wave generation by small amplitude coherent circular vortex structures, by direct global numerical simulation, describing the main features of the generated waves.

Astronomy and Astrophysics, 2010

When clusters of galaxies are viewed in projection, one cannot avoid picking up a fraction of for... more When clusters of galaxies are viewed in projection, one cannot avoid picking up a fraction of foreground/background interlopers, that lie within the virial cone, but outside the virial sphere. Structural and kinematic deprojection equations are known for the academic case of a static Universe, but not for the real case of an expanding Universe, where the Hubble flow (HF) stretches the line-of-sight distribution of velocities. Using 93 mock relaxed clusters, built from the dark matter (DM) particles of a hydrodynamical cosmological simulation, we quantify the distribution of interlopers in projected phase space (PPS), as well as the biases in the radial and kinematical structure of clusters produced by the HF. The stacked mock clusters are well fit by an m=5 Einasto DM density profile (but only out to 1.5 virial radii), with velocity anisotropy (VA) close to the Mamon-Łokas model with characteristic radius equal to that of density slope −2. The surface density of interlopers is nearly flat out to the virial radius, while their velocity distribution shows a dominant gaussian cluster-outskirts component and a flat field component. This distribution of interlopers in PPS is nearly universal, showing only small trends with cluster mass, and is quantified. A local κ=2.7 sigma velocity cut is found to return the line-of-sight velocity dispersion profile (LOSVDP) expected from the NFW density and VA profiles measured in three dimensions. The HF causes a shallower outer LOSVDP that cannot be well matched by the Einasto model for any value of κ. After this velocity cut, which removes 1 interloper out of 6, interlopers still account for 23±1% of all DM particles with projected radii within the virial radius (surprisingly very similar to the observed fraction of cluster galaxies lying off the Red Sequence) and over 60% between 0.8 and 1 virial radius. The HF causes the best-fit projected NFW or m=5 Einasto model to the stacked cluster to underestimate the true concentration measured in 3D by 6±6% (16±7%) after (before) the velocity cut. These biases in concentration are reduced by over a factor two once a constant background is included in the fit. The VA profile recovered from the measured LOSVDP by assuming the correct mass profile recovers fairly well the VA measured in 3D, with a slight, marginally significant, bias towards more radial orbits in the outer regions. These small biases in the concentration and VA of the galaxy system are overshadowed by important cluster-to-cluster fluctuations caused by cosmic variance and by the strong inefficiency caused by the limited numbers of observed galaxies in clusters. An appendix provides an analytical approximation to the surface density, projected mass and tangential shear profiles of the Einasto model. Another derives the expressions for the surface density and mass profiles of the NFW model projected on the sphere (for future kinematic modeling).

Astronomy and Astrophysics, 2007

Aims. We explore the growth and the evolution of the bar instability in stellar-gaseous disks emb... more Aims. We explore the growth and the evolution of the bar instability in stellar-gaseous disks embedded in a suitable dark matter halo evolving in a fully consistent cosmological framework. The aim of this paper is to point out the impact of different gas fractions on the bar formation, inside disks of different disk-to-halo mass ratio, and the role of the cosmological framework. Methods. We perform cosmological simulations with the same disk-to-halo mass ratios as in a previous work where the gas was not taken into account. We compare results of the new simulations with the previous ones to investigate the effect of the gas by analysing the morphology of the stellar and gaseous components, the stellar bar strength and the behaviour of its pattern speed. Results. In our cosmological simulations, inside dark-matter dominated disks, a stellar bar, lasting 10 Gyr, is still living at z = 0 even if the gaseous fraction exceeds half of the disk mass. However, in the most massive disks we find a threshold value (0.2) of the gas fraction able to destroy the bar. The stellar bar strength is enhanced by the gas and in the more massive disks higher gas fractions increase the bar pattern speed.

Monthly Notices of the Royal Astronomical Society, 2016