New Approaches for Determining the Dark Matter Content of Spiral Galaxies

Presented by Marc Seigar, University of Arkansas at Little Rock

The standard cosmological model, LCDM, is remarkably successful at reproducing the large-scale structure of the Universe. However, on smaller, galaxy-sized scales, there are several issues. High-resolution N-body simulations of LCDM structure formation predict that the central density profiles of dark matter halos should rise steeply at small radii. Observations of late-type disk galaxies and dwarf galaxies on the other hand, have shown that quite often, that mass distributions with constant density cores are preferred. This is known as the cusp/core problem. Another problem with LCDM cosmology is the Tully-Fisher zero-point problem, which refers to the fact that standard models cannot reproduce the relation between galaxy luminosity and rotational velocity without over-producing the number density of galaxies at fixed luminosity. This is a result of the theoretical prediction that halos should contract adiabatically to the formation of a visible galaxy. The problem can be resolved if this adiabatic contraction does not operate, yet galaxies like M31 (Andromeda) appear to need this contraction to explain their observed rotation curves. In this talk I will discuss new approaches we are taking that will hopefully resolve some of these issues.