Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

This contribution advocates anew method for comparing theoretical predictions to observations. Properties of virtual galaxies are computed using the hybrid model for hierarchical galaxy formation GALICS (for Galaxies In Cosmological Simulations), which takes advantage of large cosmological N-body simulations to plug in simple semi-analytic recipes describing the fate of the baryons. From such a fake galaxy catalog, one can build light cones, and project them onto virtual CCD devices, taking into account the technical characteristics of the detector/telescope. As a result, realistic mock images can be produced, which can then be directly compared to real observations.

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.