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

New Insights into Galaxy Clusters: from Simulations to Observations

The work carried out during this Thesis is framed within the field of Numerical Cosmology and focused on several broad lines intimately related which deal with the theoretical and numerical study of galaxy clusters: (i) the halo-finding problem, (ii) new improvements in cosmological simulations, and (iii) the formation and evolution of galaxy clusters. In spite of the achievements reached by Computational Cosmology in the last years, present-day hydrodynamics/N-body simulations still present important discrepancies with the observations, especially in the inner regions of massive galaxy clusters. Among these discrepancies we can cite, for instance, the breaking up of the self-similar scaling relations or the cooling flow problem. These discrepancies have motivated the idea that, besides gravity and adiabatic gas dynamics, non-gravitational processes related with the baryonic component of the Universe need to be included in our simulations. Within this context, in a complementary way to the different non-gravitational processes being included in simulations, it is crucial to properly describe different gravitational processes inherent to the hierarchical formation of cosmic structures itself. In this sense, the objective of the present work is to describe, in a consistent way, some of the heating processes associated with the hierarchical evolution of galaxy clusters in a full cosmological context. To identify the different cosmological structures and analyse their evolutionary histories, an Eulerian cosmological code and a grid-based halo finder have been used. The cosmological code used during this Thesis, MASCLET (Quilis, 2004), is an Eulerian code based on an adaptive mesh refinement (AMR) scheme able to model the coupled evolution of the dark matter and the baryonic components of the Universe. To analyse the outputs of these complex simulations, a new halo finder based on the spherical overdensity method (SO) has been developed (ASOHF, Planelles & Quilis, 2010). This finder allows us to extract the dark matter haloes (numerical counterpart of galaxies and galaxy clusters) and analyse, in a precise way, their main physical properties. Making use of these numerical tools, MASCLET and ASOHF, the role played by galaxy cluster mergers, as well as by the cosmological shock waves developed during these events, as sources of heating of the intracluster medium (ICM) has been analysed in a full cosmological context. In order to do so, two simulations have been performed with the MASCLET code. In these simulations, the unique relevant feedback mechanism considered is the gravitational, that is, the inherent to the hierarchical evolution of the Universe. Analysing these simulations it has been demonstrated that galaxy cluster mergers and cosmological shock waves play a crucial role, not only on galaxy cluster properties, but on the thermalization of the ICM. In particular, it has been demonstrated that galaxy cluster mergers have a direct influence on the existence of cool cores in the centre of massive galaxy clusters as well as on the scatter observed in the self-similar scaling relations (Planelles & Quilis, 2009). On the other hand, shock waves are also crucial in galaxy cluster properties contributing very efficiently to the virialization of haloes and the thermalization of the Universe. Moreover, it has been observed that the strength of shocks within the virial radius of galaxy clusters shows some correlation with their virial masses, being directly related with their dynamical histories.La presente Tesis se centra en varias líneas de investigación íntimamente relacionadas que tratan con el estudio teórico y numérico de los cúmulos de galaxias: (i) el problema de encontrar los halos de materia oscura, (ii) nuevas mejoras en simulaciones cosmológicas y, (iii) la formación y evolución de los cúmulos de galaxias. Las simulaciones hidrodinámicas/N-cuerpos actuales todavía presentan importantes discrepancias con las observaciones, especialmente en las regiones internas de los cúmulos de galaxias más masivos. Entre estas discrepancias podemos citar, por ejemplo, la ruptura de las relaciones de la escala auto-semejantes o el problema de los flujos de gas frío. Estas discrepancias han motivado la idea de que, además de gravedad y dinámica de gases adiabática, procesos no gravitacionales relacionados con la componente bariónica del Universo deben ser incluidos en las simulaciones. En este contexto, de forma complementaria a diferentes procesos no gravitacionales, es crucial describir de forma adecuada los distintos procesos gravitacionales inherentes a la propia formación jerárquica de la estructuras cósmicas. En este sentido, el objetivo del presente trabajo es describir, de forma auto-consistente, algunos de los procesos de calentamiento asociados a la propia evolución jerárquica de los cúmulos de galaxias en un contexto puramente cosmológico. Para ello, se ha hecho uso de un código cosmológico euleriano (MASCLET, Quilis, 2004) y un buscador de halos basado en el método de sobredensidad esférica (ASOHF, Planelles y Quilis, 2010). Haciendo uso de estos códigos, se ha analizado el papel que juegan las fusiones de cúmulos de galaxias y las ondas de choque generadas durante estos eventos como fuentes de calentamiento del medio intracúmulo en un contexto puramente cosmológico. En este sentido, se ha comprobado que las fusiones de cúmulos de galaxias influyen directamente en la existencia de núcleos fríos en el centro de los cúmulos más masivos, así como en la dispersión observada en las relaciones de escala auto-semejantes (Planelles y Quilis, 2009). Por otra parte, también se ha comprobado que las ondas de choque contribuyen eficientemente a la virialización de los halos y a la termalización del Universo

a mysterious universe revealing the bright and dark sides of the cosmos

Why is our universe as we observe it? Will it be the same forever? Understanding the nature of the main constituents of the universe is crucial to obtain a precise description of the way in which it reached its present state. Nowadays, many independent observations support a picture in which the matter content of the universe is shared between an ordinary and observable baryonic component ( ~ 5?%) and an invisible dark matter ( ~ 23?%). The remaining ~ 72?% of the universe content is in the form of a completely mysterious dark energy field. This composition emphasizes that, while ~ 95?% of our universe represents a major uncertainty for us, even the minor contribution from normal and, apparently, known matter entails important challenges for cosmologists

The imprints of galaxy cluster internal dynamics on the Sunyaev-Zeldovich effect

Forthcoming measurements of the Sunyaev-Zeldovich (SZ) effect in galaxy clusters will dramatically improve our understanding of the main intra-cluster medium (ICM) properties and how they depend on the particular thermal and dynamical state of the associated clusters. Using a sample of simulated galaxy clusters we assess the impact of the ICM internal dynamics on both the thermal and kinetic SZ effects (tSZ and kSZ, respectively). We produce synthetic maps of the SZ effect, for the simulated clusters. For each galaxy cluster in the sample, its dynamical state is estimated by using a combination of well-established indicators. We use the correlations between SZ maps and cluster dynamical state, to look for the imprints of the evolutionary events, mainly mergers, on the SZ signals. The kinetic effect shows a remarkable correlation with the dynamical state: unrelaxed clusters present a higher radial profile and an overall stronger signal at all masses and radii. Furthermore, the kSZ signal is correlated with rotation for relaxed clusters, while for the disturbed systems the effect is dominated by other motions such as bulk flows, turbulence, etc. The kSZ effect shows a dipolar pattern when averaging over cluster dynamical classes, especially for the relaxed population. This feature can be exploited to stack multiple kSZ maps in order to recover a stronger dipole signal that would be correlated with the global rotation properties of the sample. The SZ effect can be used as a tool to estimate the dynamical state of galaxy clusters, especially to segregate those clusters with a quiescent evolution from those with a rich record of recent merger events. Our results suggest that the forthcoming observational data measuring the SZ signal in clusters could be used as a complementary strategy to classify the evolutionary history of galaxy clusters.Comment: 13 pages. 11 figures. Accepted for publication in A&

On the nature of hydrostatic equilibrium in galaxy clusters

In this paper we investigate the level of hydrostatic equilibrium (HE) in the intra-cluster medium of simu-lated galaxy clusters, extracted from state-of-the-art cosmological hydrodynamical simulations performed withthe Smoothed-Particle-Hydrodynamic code GADGET-3. These simulations include several physical processes,among which stellar and AGN feedback, and have been performed with an improved version of the code thatallows for a better description of hydrodynamical instabilities and gas mixing processes. Evaluating the radialbalance between the gravitational and hydrodynamical forces, via the gas accelerations generated, we effectivelyexamine the level of HE in every object of the sample, its dependence on the radial distance from the center and onthe classification of the cluster in terms of either cool-coreness or dynamical state. We find an average deviation of10?20% out to the virial radius, with no evident distinction between cool-core and non-cool-core clusters. Instead,we observe a clear separation between regular and disturbed systems, with a more significant deviation from HEfor the disturbed objects. The investigation of the bias between the hydrostatic estimate and the total gravitatingmass indicates that, on average, this traces very well the deviation from HE, even though individual cases showa more complex picture. Typically, in the radial ranges where mass bias and deviation from HE are substantiallydifferent, the gas is characterized by a significant amount of random motions ( 30 per cent), relative to thermalones. As a general result, the HE-deviation and mass bias, at given interesting distance from the cluster center, arenot very sensitive to the temperature inhomogeneities in the gas.Fil: Biffi, Verónica. Università degli Studi di Trieste; Italia. Osservatorio Astronomico di Trieste; ItaliaFil: Borgani, Stefano. Università degli Studi di Trieste; Italia. Osservatorio Astronomico di Trieste; ItaliaFil: Murante, Giuseppe. Osservatorio Astronomico di Trieste; ItaliaFil: Rasia, Elena. Osservatorio Astronomico di Trieste; Italia. University of Michigan; Estados UnidosFil: Planelles, Susana. Osservatorio Astronomico di Trieste; Italia. Universidad de Valencia; EspañaFil: Granato, Gian Luigi. Istituto Nazionale di Astrofisica; Italia. Osservatorio Astronomico di Trieste; ItaliaFil: Ragone Figueroa, Cinthia Judith. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Beck, Alexander. University Observatory Munich; Alemania. Universitat Genzentrum Der Ludwing-Maximilians; AlemaniaFil: Gaspari, Massimo. University of Princeton; Estados UnidosFil: Dolag, Klaus. University Observatory Munich; Alemania. Universitat Genzentrum Der Ludwing-Maximilians; Alemani