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Abstract:

This contribution reports on our first efforts to simulate a multiphase interstellar medium on a kiloparsec scale in three dimensions with the stars and gas modeled self-consistently. Starting from inhomogenous initial conditions, our closed box simulations follow the gas as it cools and collapses under its own self-gravity to form stars which eventually return material and energy back through supernovae explosions and winds.

Abstract:

We present the first high-resolution n-body simulations of the fragmentation of dark matter filaments. Such fragmentation occurs in top-down scenarios of structure formation, when the dark matter is warm instead of cold. In a previous paper (Knebe et al. 2002, hereafter Paper I), we showed that WDM differs from the standard Cold Dark Matter (CDM) mainly in the formation history and large-scale distribution of low-mass haloes, which form later and tend to be more clustered in WDM than in CDM universes, tracing more closely the filamentary structures of the cosmic web. Therefore, we focus our computational effort in this paper on one particular filament extracted from a WDM cosmological simulation and compare in detail its evolution to that of the same CDM filament. We find that the mass distribution of the halos forming via fragmentation within the filament is broadly peaked around a Jeans mass of a few 10^9 Msun, corresponding to a gravitational instability of smooth regions with an overdensity contrast around 10 at these redshifts. Our results confirm that WDM filaments fragment and form gravitationally bound haloes in a top-down fashion, whereas CDM filaments are built bottom-up, thus demonstrating the impact of the nature of the dark matter on dwarf galaxy properties.

Abstract:

We present the first high-resolution N-body simulations of the fragmentation of dark matter filaments. Such fragmentation occurs in top-down scenarios of structure formation, when the dark matter is warm instead of cold. In a previous paper, we showed that warm dark matter (WDM) differs from the standard cold dark matter (CDM) mainly in the formation history and large-scale distribution of low-mass haloes, which form later and tend to be more clustered in WDM than in CDM universes, tracing the filamentary structures of the cosmic web more closely. Therefore, we focus our computational effort in this paper on one particular filament extracted from a WDM cosmological simulation and compare in detail its evolution to that of the same CDM filament. We find that the mass distribution of the haloes forming via fragmentation within the filament is broadly peaked around a Jeans mass of a few 109 M ⊙, corresponding to a gravitational instability of smooth regions with an overdensity contrast around 10 at these redshifts. Our results confirm that WDM filaments fragment and form gravitationally bound haloes in a top-down fashion, whereas CDM filaments are built bottom-up, thus demonstrating the impact of the nature of the dark matter on dwarf galaxy properties.

Abstract:

This paper illustrates how mock observational samples of high-redshift galaxies with sophisticated selection criteria can be extracted from the predictions of GALICS, a hybrid model of hierarchical galaxy formation that couples the outputs of large cosmological simulations and semi-analytic recipes to describe dark matter collapse and the physics of baryons respectively. As an example of this method, we focus on the properties of Lyman Break Galaxies at redshift 3. With the MOMAF software package described in a companion paper, we generate a mock observational sample with selection criteria as similar as possible to those implied in the actual observations of z = 3 LBGs by Steidel et al.(1995). Our model predictions are in good agreement with the observed number density and 2D correlation function. We investigate the optical/IR luminosity budget as well as several other physical properties of LBGs and find them to be in general agreement with observed values. Looking into the future of these LBGs we predict that 75% of them end up as massive ellipticals today, even though only 35% of all our local ellipticals are predicted to have a LBG progenitor. In spite of some shortcomings, this new 'mock observation' method clearly represents a necessary first step toward a more accurate comparison between hierarchical models of galaxy formation and real observational surveys.