Galaxy formation and evolution

Abstract:

Observations on galactic scales seem to be in contradiction with recent high resolution N-body simulations. This so-called cold dark matter (CDM) crisis has been addressed in several ways, ranging from a change in fundamental physics by introducing self-interacting cold dark matter particles to a tuning of complex astrophysical processes such as global and/or local feedback. All these efforts attempt to soften density profiles and reduce the abundance of satellites in simulated galaxy halos. In this contribution we are exploring the differences between a Warm Dark Matter model and a CDM model where the power on a certain scale is reduced by introducing a narrow negative feature ('dip'). This dip is placed in a way so as to mimic the loss of power in the WDM model: both models have the same integrated power out to the scale where the power of the Dip model rises to the level of the unperturbed CDM spectrum again. Using N-body simulations we show that that the new Dip model appears to be a viable alternative to WDM while being based on different physics: where WDM requires the introduction of a new particle species the Dip stems from a nonstandard inflationary period. If we are looking for an alternative to the currently challenged standard ΛCDM structure formation scenario, neither the ΛWDM nor the new Dip model can be ruled out with respect to the analysis presented in this contribution. They both make very similar predictions and the degeneracy between them can only be broken with observations yet to come.

Abstract:

We present results from a new and unique integral-field spectrograph, SAURON. It has a large field of view and high throughput and is primarily built for the study of stellar & gaseous kinematics and stellar populations in galaxies. Its aim is to carry out a systematic survey of the velocity fields, velocity dispersions, and line-strength distributions of nearby ellipticals, lenticular galaxies and spiral bulges.

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, 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.