Dwarf Galaxies in Voids: Dark Matter Halos and Gas Cooling

Galaxy surveys have shown that luminous galaxies are mainly distributed in large filaments and galaxy clusters. The remaining large volumes are virtually devoid of luminous galaxies. This is in concordance with the formation of the large-scale structure in Universe as derived from cosmological simulations. However, the numerical results indicate that cosmological voids are abundantly populated with dark matter haloes which may in principle host dwarf galaxies. Observational efforts have in contrast revealed, that voids are apparently devoid of dwarf galaxies. We investigate the formation of dwarf galaxies in voids by hydrodynamical cosmological simulations. Due to the cosmic ultra-violet background radiation low-mass haloes show generally are reduced baryon fraction. We determine the characteristic mass below which dwarf galaxies are baryon deficient. We show that the circular velocity below which the accretion of baryons is suppressed is approximately 40 km/s. The suppressed baryon accretion is caused by the photo-heating due to the UV-background. We set up a spherical halo model and show that the effective equation of state of the gas in the periphery of dwarf galaxies determines the characteristic mass. This implies that any process which heats the gas around dwarf galaxies increases the characteristic mass and thus reduces the number of observable dwarf galaxies.Comment: 23 pages. To appear in Advances in Astronomy, Dwarf-Galaxy Cosmology issu

Constrained Local UniversE Simulations (CLUES)

The local universe is the best known part of our universe. Within the CLUES project (http://clues-project.org - Constrained Local UniversE Simulations) we perform numerical simulations of the evolution of the local universe. For these simulations we construct initial conditions based on observational data of the galaxy distribution in the local universe. Here we review the technique of these constrained simulations. In the second part we summarize our predictions of a possible Warm Dark Matter cosmology for the observed local distribution of galaxies and the local spectrum of mini-voids as well as a study of the satellite dynamics in a simulated Local Group.Comment: High resolution version on http://clues-project.org To be published in: Proceedings of "High Performance Computing in Science and Engineering, Garching/Munich 2009", Springer-Verlag, 201

Confrontation of a Double Inflationary Cosmological Model with Observations

CDM models with non-scale-free step-like spectra of adiabatic perturbations produced in a realistic double inflationary model are compared with recent observational data. The model contains two additional free parameters relatively to the standard CDM model with the flat ($n=1$) initial spectrum. Results of the COBE experiment are used for the determination of a free overall spectrum normalization. Then predictions for the galaxy biasing parameter, the variance for "counts in cells", the galaxy angular correlation function, bulk flow peculiar velocities and the Mach number test are obtained. Also considered are conditions for galaxy and quasar formation. Observational data strongly restricts allowed values for the two remaining model parameters. However, a non-empty region for them satisfying all considered tests is found.Comment: 17 pages and 4 figures obtainable by request, LaTex, AIP 93-1