arXiv subjects

Vicent Quilis

Publications and source records attributed to Vicent Quilis.

50 records · Page 3Linked to original sources

arXiv2009

Galaxy cluster mergers

We present the results of an Eulerian adaptive mesh refinement (AMR) hydrodynamical and N-body simulation in a $Λ$CDM cosmology. The simulation incorporates common cooling and heating processes for primordial gas. A specific halo finder has been designed and applied in order to extract a sample of galaxy clusters directly obtained from the simulation without considering any resimulating scheme. We have studied the evolutionary history of the cluster halos, and classified them into three categories depending on the merger events they have undergone: major mergers, minor mergers, and relaxed clusters. The main properties of each one of these classes and the differences among them are discussed. The collisions among galaxy clusters are produced naturally by the non-linear evolution in the simulated cosmological volume, no controlled collisions have been considered. We pay special attention to discuss the role of merger events as a source of feedback and reheating, and their effects on the existence of cool cores in galaxy clusters, as well as in the scaling relations.

astro-ph.CO↗

arXiv2008

Quantifying the heart of darkness with GHALO - a multi-billion particle simulation of our galactic halo

We perform a series of simulations of a Galactic mass dark matter halo at different resolutions, our largest uses over three billion particles and has a mass resolution of 1000 M_sun. We quantify the structural properties of the inner dark matter distribution and study how they depend on numerical resolution. We can measure the density profile to a distance of 120 pc (0.05% of R_vir) where the logarithmic slope is -0.8 and -1.4 at (0.5% of R_vir). We propose a new two parameter fitting function that has a linearly varying logarithmic density gradient which fits the GHALO and VL2 density profiles extremely well. Convergence in the density profile and the halo shape scales as N^(-1/3), but the shape converges at a radius three times larger at which point the halo becomes more spherical due to numerical resolution. The six dimensional phase-space profile is dominated by the presence of the substructures and does not follow a power law, except in the smooth under-resolved inner few kpc.

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arXiv2007

AMR simulations of the low T/|W| bar-mode instability of neutron stars

It has been recently argued through numerical work that rotating stars with a high degree of differential rotation are dynamically unstable against bar-mode deformation, even for values of the ratio of rotational kinetic energy to gravitational potential energy as low as O(0.01). This may have implications for gravitational wave astronomy in high-frequency sources such as core collapse supernovae. In this paper we present high-resolution simulations, performed with an adaptive mesh refinement hydrodynamics code, of such low T/|W| bar-mode instability. The complex morphological features involved in the nonlinear dynamics of the instability are revealed in our simulations, which show that the excitation of Kelvin-Helmholtz-like fluid modes outside the corotation radius of the star leads to the saturation of the bar-mode deformation. While the overall trends reported in an earlier investigation are confirmed by our work, we also find that numerical resolution plays an important role during the long-term, nonlinear behaviour of the instability, which has implications on the dynamics of rotating stars and on the attainable amplitudes of the associated gravitational wave signals.

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arXiv2004

A new multidimensional AMR Hydro+Gravity Cosmological code

A new cosmological multidimensional hydrodynamic and N-body code based on an Adaptive Mesh Refinement scheme is described and tested. The hydro part is based on modern high-resolution shock-capturing techniques, whereas N-body approach is based on the Particle Mesh method. The code has been specifically designed for cosmological applications. Tests including shocks, strong gradients, and gravity have been considered. A cosmological test based on Santa Barbara cluster is also presented. The usefulness of the code is discussed. In particular, this powerful tool is expected to be appropriate to describe the evolution of the hot gas component located inside asymmetric cosmological structures.

astro-ph↗

arXiv2001

Bubbles, feedback and the intra-cluster medium: three-dimensional hydrodynamic simulations

We use a three dimensional hydrodynamical code to simulate the effect of energy injection on cooling flows in the intracluster medium. Specifically, we compare a simulation of a 10$^{15}$ $M_\odot$ cluster with radiative cooling only, with a second simulation in which thermal energy is injected 31 $\kpc$ off-centre, over 64 kpc$^{3}$ at a rate of $4.9\times 10^{44} \ergs$ for 50 Myr. The heat injection forms a hot, low density bubble which quickly rises, dragging behind it material from the cluster core. The rising bubble pushes with it a shell of gas which expands and cools. We find the appearance of the bubble in X-ray temperature and luminosity to be in good qualitative agreement with recent {\it Chandra} observations of cluster cores. Toward the end of the simulation, at 600 Myr, the displaced gas begins to fall back toward the core, and the subsequent turbulence is very efficient at mixing the low and high entropy gas. The result is that the cooling flow is disrupted for up to $\sim 50$ Myr after the injection of energy ceases. Thus, this mechanism provides a very efficient method for regulating cooling flows, if the injection events occur with a 1:1 duty cycle.

astro-ph↗

arXiv2001

Where are the high velocity clouds?

Recent observations of high velocity clouds (HVCs) have revealed compression fronts and tail shaped features of HI suggesting that they are interacting with external medium. We perform 3-D hydro-dynamical simulations of HVCs moving through a diffuse hot gaseous component, investigating the behaviour of both extra-galactic dark matter dominated HVCs and nearby pure gas clouds that may be accreting onto the Galactic disk via a Galactic fountain. Both scenarios can give rise to similar features as observed if the external medium has a density $>10^{-4}$ cm$^{-3}$. Observations suggest that this may be too high for a hot ionised halo or intergalactic gas and supports the Galactic fountain origin, a model that can also account for the high fraction of HVCs with tails and asymmetrical morphologies.

astro-ph↗

arXiv2000

Dynamical effects on galaxies in clusters

The observed morphological evolution since z ~ 0.5 within galaxy clusters provides evidence for a hierarchical universe. This evolution is driven by dynamical effects that operate within the cluster environment -- suppression of star-formation by ram-pressure and viscous stripping of the intra-galactic medium and tidal heating of disks by gravitational encounters.

astro-ph↗

arXiv2000

Gone with the wind: the origin of S0 galaxies in clusters

We present the first 3-dimensional high resolution hydro-dynamical simulations of the interaction between the hot ionised intra-cluster medium and the cold interstellar medium of spiral galaxies. Ram pressure and turbulent/viscous stripping removes 100% of the atomic hydrogen content of luminous galaxies like the Milky Way within 100 million years. These mechanisms naturally account for the morphology of S0 galaxies, the rapid truncation of star formation implied by spectroscopic observations, as well as a host of observational data on the HI morphology of galaxies in clusters.

astro-ph↗

arXiv2000

Collisional versus Collisionless Dark Matter

We compare the structure and substructure of dark matter halos in model universes dominated by collisional, strongly self interacting dark matter (SIDM) and collisionless, weakly interacting dark matter (CDM). While SIDM virialised halos are more nearly spherical than CDM halos, they can be rotationally flattened by as much as 20% in their inner regions. Substructure halos suffer ram-pressure truncation and drag which are more rapid and severe than their gravitational counterparts tidal stripping and dynamical friction. Lensing constraints on the size of galactic halos in clusters are a factor of two smaller than predicted by gravitational stripping, and the recent detection of tidal streams of stars escaping from the satellite galaxy Carina suggests that its tidal radius is close to its optical radius of a few hundred parsecs --- an order of magnitude smaller than predicted by CDM models but consistent with SIDM. The orbits of SIDM satellites suffer significant velocity bias $σ_{SIDM}/σ_{CDM}=0.85$ and are more circular than CDM, $β_{SIDM}} \approx 0.5$, in agreement with the inferred orbits of the Galaxy's satellites. In the limit of a short mean free path, SIDM halos have singular isothermal density profiles, thus in its simplest incarnation SIDM is inconsistent with galactic rotation curves.

astro-ph↗

arXiv1999

Gravitational waves from galaxy cluster distributions

Galaxy clusters are sources of gravitational radiation. The main aim of this paper is to give numerical estimates and theoretical description of the relevant features of the gravitational radiation coming from an appropriate spatial distributions of galaxy clusters. Since no analytical approaches are currently available to describe the strongly nonlinear regime, our numerical approach - combining numerical simulations with statistical arguments - seems to be an useful way of studying the main features of that radiation. Although far to be detectable with present technology, we advance some ideas about future observational strategies and its cosmological implications.

astro-ph↗

arXiv1998

Gravitational waves from galaxy clusters: a new observable effect

A rich galaxy cluster showing strong resemblance with the observed ones is simulated. Cold dark matter spectrum, Gaussian statistics, flat universe, and two components -- baryonic gas plus dark matter particles -- are considered. We have calculated the gravitational-wave output during the epoch of the fully nonlinear and nonsymmetric cluster evolution. The amplitudes and frequencies of the resulting gravitational waves are estimated. Since frequencies are very small --of the order of $10^{-17} Hz$ -- a complete pulse cannot be observed during an admissible integration time; nevertheless, it is proved that these waves can produce an interesting secular effect which appears to be observable with current technology.

astro-ph↗

arXiv1998

On the role of shock waves in galaxy cluster evolution

Numerical simulations of galaxy clusters including two species -- baryonic gas and dark matter particles --are presented. Cold Dark Matter spectrum, Gaussian statistics and flat universe are assumed. The dark matter component is evolved numerically by means of a standard particle mesh method. The evolution of the baryonic component has been studied numerically by using a multidimensional (3D) hydrodynamical code based on modern high resolution shock capturing techniques. These techniques are specially designed for treating accurately complex flows in which shocks appear and interact. With this picture, the role of shock waves in the formation and evolution of rich galaxy clusters is analyzed. Our results display two well differenced morphologies of the shocked baryonic matter: filamentary at early epochs and quasi-spherical at low redshifts.

astro-ph↗

arXiv1997

Secondary gravitational anisotropies in open universes

The applicability of the potential approximation in the case of open universes is tested. Great Attractor-like structures are considered in the test. Previous estimates of the Cosmic Microwave background anisotropies produced by these structures are analyzed and interpreted. The anisotropies corresponding to inhomogeneous ellipsoidal models are also computed. It is proved that, whatever the spatial symmetry may be, Great Attractor-like objects with extended cores (radius $\sim 10h^{-1}$),located at redshift $z=5.9$ in an open universe with density parameter $Ω_{0}=0.2$, produce secondary gravitational anisotropies of the order of $10^{-5}$ on angular scales of a few degrees. This anisotropy appears to be an integrated effect along the photon geodesics. Its angular scale is much greater than that subtended by the Great Attractor itself. This is understood taking into account that the integrated effect is produced by the variations of the gravitational potential, which seem to be important in large regions subtending angular scales of various degrees. As a result of the large size of these regions, the spatial curvature of the universe becomes important and, consequently, significant errors ($\sim 30$ per cent) arise in estimations based on the potential approximation.

astro-ph↗

arXiv1996

A multidimensional hydrodynamic code for structure evolution in cosmology

A cosmological multidimensional hydrodynamic code is described and tested. This code is based on modern high-resolution shock-capturing techniques. It can make use of a linear or a parabolic cell reconstruction as well as an approximate Riemann solver. The code has been specifically designed for cosmological applications. Two tests including shocks have been considered: the first one is a standard shock tube and the second test involves a spherically symmetric shock. Various additional cosmological tests are also presented. In this way, the performance of the code is proved. The usefulness of the code is discussed; in particular, this powerful tool is expected to be useful in order to study the evolution of the hot gas component located inside nonsymmetric cosmological structures.

astro-ph↗