Vicent Quilis

Gone with the Wind: The Origin of S0 Galaxies in Clusters

We present three-dimensional, high-resolution hydrodynamical simulations of the interaction between the hot ionized intracluster medium and the cold interstellar medium of spiral galaxies. Ram pressure and turbulent/viscous stripping remove 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 and the rapid truncation of star formation implied by spectroscopic observations, as well as a host of observational data on the neutral hydrogen (HI) morphology of galaxies in clusters.

Haloes gone MAD: The Halo-Finder Comparison Project

We present a detailed comparison of fundamental dark matter halo properties retrieved by a substantial number of different halo finders. These codes span a wide range of techniques including friends-of-friends, spherical-overdensity and phase-space-based algorithms. We

Bubbles, feedback and the intracluster 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 1015-M⊙ cluster with radiative cooling only with a second simulation in which thermal energy is injected 31xa0kpc off-centre, over 64xa0kpc3 at a rate of for 50xa0Myr. 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 Chandra observations of cluster cores. Toward the end of the simulation, at 600xa0Myr, 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 ∼xa050xa0Myr 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.

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 virialized 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 2 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 models. The orbits of SIDM satellites suffer significant velocity bias, sigmaSIDM&solm0;sigmaCDM=0.85, and are more circular than CDM satellites, betaSIDM approximately 0.5, in agreement with the inferred orbits of the Galaxys 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.

Where are the high velocity clouds

Recent observations of high-velocity clouds (HVCs) have revealed compression fronts and tail-shaped features of H I, suggesting that they are interacting with an external medium. We perform three-dimensional hydrodynamical simulations of HVCs moving through a diffuse hot gaseous component, investigating the behavior of both extragalactic 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 greater than 10-4 cm-3. Observations suggest that this may be too high for a hot ionized 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.

Cosmic microwave background anisotropy: deviations from Gaussianity caused by non-linear gravity

Non-linear evolution of cosmological energy density fluctuations triggers deviations from Gaussianity in the temperature distribution of the cosmic microwave background. A method to estimate these deviations is proposed. N-body simulations – in a ΛCDM cosmology – are used to simulate the strongly non-linear evolution of cosmological structures. It is proved that these simulations can be combined with the potential approximation to calculate the statistical moments of the CMB anisotropies produced by non-linear gravity. Some of these moments are computed and the resulting values are different from those corresponding to Gaussianity.

The Origin of S0 Galaxies in Clusters

We study the morphological changes induced by the Intra Cluster Medium (ICM) on spiral galaxies when they move through the core cluster. The galaxies are modeled as a thin exponential slab of cold gas, a stellar disk, bulge, and dark matter halo. The interaction of galaxy with the ICM is studied by means of a 3-dimensional non-symmetric high-resolution hydrodynamic code for gaseous matter, coupled with a N-body code for the collision-less matter. Several parameter ranging reasonable values for ICM and galaxies have been considered. We conclude that, for some scenarios compatible with observations, ram-pressure stripping could suffice to explain the Butcher—Oemler effect and the morphologic transformation of spiral galaxies in lenticulars (S0).