Gerard Lemson

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We study the biasing relation between dark-matter halos or galaxies and the underlying mass distribution, using cosmological N -body simulations in which galaxies are modelled via semi-analytic recipes. The nonlinear, stochastic biasing is quantified in terms of the mean biasing function and the scatter about it as a function of time, scale and object(More)
We present the Millennium-II Simulation (MS-II), a very large N -body simulation of dark matter evolution in the concordance ΛCDM cosmology. The MS-II assumes the same cosmological parameters and uses the same particle number and output data structure as the original Millennium Simulation (MS), but was carried out in a periodic cube one-fifth the size (100(More)
We present the online MultiDark Database – a Virtual Observatory-oriented, relational database for hosting various cosmological simulations. The data is accessible via an SQL (Structured Query Language) query interface, which also allows users to directly pose scientific questions, as shown in a number of examples in this paper. Further examples for the(More)
1. California Institute of Technology, California Ave, 91126, Pasadena, CA 2. Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching, Germany 3. Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Moenchhofstr. 12-14, 69120, Heidelberg, Germany 4. Max-Planck-Institut für extraterrestrische Physik,(More)
The field of e-science currently faces many challenges. Among the most important ones are the analysis of huge volumes of scientific data and the connection of various sciences and communities, thus enabling scientists to share scientific interests, data, and research results. These issues can be addressed by processing large data volumes on-thefly in the(More)
The Millennium Run is the largest simulation of the formation of structure within the ΛCDM cosmogony so far carried out. It uses 1010 particles to follow the dark matter distribution in a cubic region 500h−1Mpc on a side, and has a spatial resolution of 5 h−1kpc. Application of simplified modelling techniques to the stored output of this calculation allows(More)
We simulate the formation and evolution of the local galaxy population starting from initial conditions with a smoothed linear density field which matches that derived from the IRAS 1.2 Jy galaxy survey. Our simulations track the formation and evolution of all dark matter haloes more massive than 1011M⊙ out to a distance of 8000 km s −1 from the Milky Way.(More)
We use large N-body simulations of dissipationless gravitational clustering in cold dark matter (CDM) cosmologies to study whether the properties of dark matter halos are affected by their environment. We look for correlations between the masses, formation redshifts, concentrations, shapes and spins of halos and the overdensity of their local environment.(More)
The formation of dark matter halos tends to occur anisotropically along the filaments of the Cosmic Web, which induces both ellipticity-ellipticity (EE) correlations between the shapes of halos, as well as ellipticity-direction (ED) cross-correlations between halo shapes and the directions to neighboring halos. We analyze the halo catalogue and the(More)