Non-Standard Structure Formation Scenarios

Abstract

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 non-standard 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.

Angular Momentum Profiles of Warm Dark Matter Halos

“…This result is in agreement with findings of Knebe et al (2001) who reported systematically lower spins for halos in the WDM models with higher filtering mass. We showed that the addition of initial thermal velocities resulted in even lower spins in the WDM halos as well as a significantly larger misaligned (negative j) mass fraction.…”

“…It was shown that WDM does help to alleviate problems of CDM with halo density profiles and, possibly, the spatial distribution of dwarf galaxies (Peebles 2001). In addition, Knebe et al (2001) compared specific angular momentum distribution in CDM halos to that of the halos formed in WDM cosmology and found no systematic difference. However, they studied halos with masses much higher than the filtering mass of the simulation and neglected the thermal velocities of the WDM particles.…”

“…Among the most popular is the recommendation that warm dark matter (WDM) be substituted for CDM (e.g., Hogan & Dalcanton 2000). This acts to suppress power relative to CDM on scales below the filtering scale R f , which is related to the WDM particle mass via R p Knebe et al 2001;Eke, Navarro, & Steinmetz 2001). It was shown that WDM does help to alleviate problems of CDM with halo density profiles and, possibly, the spatial distribution of dwarf galaxies (Peebles 2001).…”

Is Gravitational Lensing by Intercluster Filaments Always Negligible?

“…Our assumption is based on the HDM cosmology (see x 1) and on the fact that filaments are generic 7 and have similar characteristics in hot dark matter ( HDM ) and CDM scenarios ( Knebe 2003;Knebe et al 2002;Bode et al 2001). For instance, neutrinos are known to collapse into sheets and filaments in HDM simulations.…”

“…Without resorting to cold dark matter (CDM ), the modified Newtonian dynamics ( MOND) paradigm ( Milgrom 1983;Bekenstein & Milgrom 1984) is known to reproduce galaxy scaling relations like the Tully-Fisher relation ( Tully & Fisher 1977), the Faber-Jackson law ( Faber & Jackson 1976), and the fundamental plane ( Djorgovski & Davis 1987) as well as the rotation curves of individual galaxies over five decades in mass (Sanders & McGaugh 2002;Bekenstein 2006;Sanders & Noordermeer 2007;Milgrom & Sanders 2007, 2003Nipoti et al 2007;Famaey et al 2007a). In particular, the recent kinematic analysis of tidal dwarf galaxies by Bournaud et al (2007) is very hard to explain within the classical CDM framework, while it is in accordance with MOND Milgrom 2007).…”