A geometrical model for the catalogs of galaxies

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Abstract

The 3D network originated by the faces of irregular Poissonian Voronoi polyhedra may represent the backbone on which the galaxies are originated. As a consequence the spatial appearance of the catalogs of galaxies can be reproduced. The selected catalogs to simulate are the 2dF Galaxy Redshift Survey and the Third Reference Catalog of Bright Galaxies. In order to explain the number of observed galaxies for a given flux/magnitude as a function of the redshift, the photometric properties of the galaxies should be carefully examined from both the astronomical and theoretical point of view. The statistics of the Voronoi normalized volume is modeled by two distributions and the Eridanus super-void is identified as the largest volume belonging to the Voronoi polyhedron. The behavior of the correlation function for galaxies is simulated by adopting the framework of thick faces of Voronoi polyhedra on short scales, while adopting standard arguments on large scales.

Translated abstract

La red 3D que se origina por las caras de los polihedros irregulares poissonianos de Voronoi podría representar la estructura básica para la formación de galaxias. En consecuencia, la apariencia espacial de los catálogos de galaxias podría reproducirse. Los catálogos seleccionados para la simulación fueron el 2dF Galaxy Redshift Survey y el Third Reference Catalog of Bright Galaxies. Para explicar el número observado de galaxias con un flujo (o magnitud) dado como función del corrimiento al rojo deben examinarse cuidadosamente las propiedades fotométricas de las galaxias, tanto desde un punto de vista astronómico como teórico. La estadística del volumen de Voronoi normalizado se modela por dos distribuciones, y el super-hueco en Eridanus se identifica como el mayor volumen perteneciente al polihedro de Voronoi. El comportamiento de la función de correlación de las galaxias se simula adoptando el esquema de caras gruesas de polihedros de Voronoi para escalas pequeñas, y conservando los argumentos usuales para escalas grandes.

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Rapid planetesimal formation in turbulent circumstellar discs

Anders Johansen, Jeffrey S. Oishi, Mordecai-Mark Mac Low … (2007)

The initial stages of planet formation in circumstellar gas discs proceed via dust grains that collide and build up larger and larger bodies (Safronov 1969). How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem (Dominik et al. 2007): boulders stick together poorly (Benz 2000), and spiral into the protostar in a few hundred orbits due to a head wind from the slower rotating gas (Weidenschilling 1977). Gravitational collapse of the solid component has been suggested to overcome this barrier (Safronov 1969, Goldreich & Ward 1973, Youdin & Shu 2002). Even low levels of turbulence, however, inhibit sedimentation of solids to a sufficiently dense midplane layer (Weidenschilling & Cuzzi 1993, Dominik et al. 2007), but turbulence must be present to explain observed gas accretion in protostellar discs (Hartmann 1998). Here we report the discovery of efficient gravitational collapse of boulders in locally overdense regions in the midplane. The boulders concentrate initially in transient high pressures in the turbulent gas (Johansen, Klahr, & Henning 2006), and these concentrations are augmented a further order of magnitude by a streaming instability (Youdin & Goodman 2005, Johansen, Henning, & Klahr 2006, Johansen & Youdin 2007) driven by the relative flow of gas and solids. We find that gravitationally bound clusters form with masses comparable to dwarf planets and containing a distribution of boulder sizes. Gravitational collapse happens much faster than radial drift, offering a possible path to planetesimal formation in accreting circumstellar discs.

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The Dicke Quantum Phase Transition with a Superfluid Gas in an Optical Cavity

Ferdinand Brennecke, Tilman Esslinger, Christine Guerlin … (2009)

A phase transition describes the sudden change of state in a physical system, such as the transition between a fluid and a solid. Quantum gases provide the opportunity to establish a direct link between experiment and generic models which capture the underlying physics. A fundamental concept to describe the collective matter-light interaction is the Dicke model which has been predicted to show an intriguing quantum phase transition. Here we realize the Dicke quantum phase transition in an open system formed by a Bose-Einstein condensate coupled to an optical cavity, and observe the emergence of a self-organized supersolid phase. The phase transition is driven by infinitely long-ranged interactions between the condensed atoms. These are induced by two-photon processes involving the cavity mode and a pump field. We show that the phase transition is described by the Dicke Hamiltonian, including counter-rotating coupling terms, and that the supersolid phase is associated with a spontaneously broken spatial symmetry. The boundary of the phase transition is mapped out in quantitative agreement with the Dicke model. The work opens the field of quantum gases with long-ranged interactions, and provides access to novel quantum phases.