Is ram-pressure stripping an efficient mechanism to remove gas in galaxies?

We study how the gas in a sample of galaxies (M* > 10e9 Msun) in clusters, obtained in a cosmological simulation, is affected by the interaction with the intra-cluster medium (ICM). The dynamical state of each elemental parcel of gas is studied using the total energy. At z ~ 2, the galaxies in the simulation are evenly distributed within clusters, moving later on towards more central locations. In this process, gas from the ICM is accreted and mixed with the gas in the galactic halo. Simultaneously, the interaction with the environment removes part of the gas. A characteristic stellar mass around M* ~ 10e10 Msun appears as a threshold marking two differentiated behaviours. Below this mass, galaxies are located at the external part of clusters and have eccentric orbits. The effect of the interaction with the environment is marginal. Above, galaxies are mainly located at the inner part of clusters with mostly radial orbits with low velocities. In these massive systems, part of the gas, strongly correlated with the stellar mass of the galaxy, is removed. The amount of removed gas is sub-dominant compared with the quantity of retained gas which is continuously influenced by the hot gas coming from the ICM. The analysis of individual galaxies reveals the existence of a complex pattern of flows, turbulence and a constant fuelling of gas to the hot corona from the ICM that could make the global effect of the interaction of galaxies with their environment to be substantially less dramatic than previously expected.Comment: 17 pages, 12 figures, accepted for publication in MNRA

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.Comment: 34 pages , LaTex with aasms4.sty, 7 postscript figures, figure 4 available by e-mail, tared , gziped and uuencoded. Accepted Ap

Sedation During Neurocritical Care

AbstractSedation is an essential therapeutic strategy in the care of neurocritical patients. Intravenous sedative agents are the most widely used, with promising alternatives (dexmedetomidine, ketamine, and volatile agents) to propofol and midazolam arising. Studies designed to evaluate superiority and avoid biases are required. A neurological awakening test is safe in most patients. Potential risks and benefits of limiting deep sedation and daily interruption of sedation in these patients remain unclear. The aim of this review was to report recent clinical evidence on sedation in this subgroup of patients, focusing on its effects on clinical prognosis

Satellites around massive galaxies since z∼\sim2: confronting the Millennium simulation with observations

Minor merging has been postulated as the most likely evolutionary path to produce the increase in size and mass observed in the massive galaxies since z$\sim$2. In this Letter, we test directly this hypothesis comparing the population of satellites around massive galaxies in cosmological simulations versus the observations. We use state-of-the-art, publically available, Millennium I and II simulations and the associated semi-analytical galaxy catalogues to explore the time evolution of the fraction of massive galaxies that have satellites, the number of satellites per galaxy, the projected distance at which the satellite locate from the host galaxy, and the mass ratio between the host galaxies and their satellites. The three virtual galaxy catalogues considered here, overproduce the fraction of galaxies with satellites by a factor ranging between 1.5 and 6 depending on the epoch, whereas the mean projected distance and ratio of the satellite mass over host mass are in closer agreement with data. The larger pull of satellites in the semi-analytical samples could suggest that the size evolution found in previous hydrodynamical simulations is an artifact due to the larger number of infalling satellites compared to the real Universe. These results advise to revise the physical ingredients implemented in the semi-analytical models in order to reconcile the observed and computed fraction of galaxies with satellites, and eventually, it would leave some room to other mechanisms explaining the galaxy size growth not related to the minor merging.Comment: Accepted for publication in ApJ Letter

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 $\Omega_{0}=0.2$, 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.Comment: 26 pages, Latex, 4 postscript figures, accepted MNRA