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Colloquium: David Sand

Date:
-
Location:
155 Chemistry-Physics Bldg

Testing the Cold Dark Matter Paradigm for Structure Formation from Dwarf Galaxy to Galaxy Cluster Scales                                                                     

                                                Department of Physics and Astronomy

                                                                  UC Santa Barbara

The Cold Dark Matter (CDM) paradigm of structure formation has been extremely successful in explaining the large scale properties of the universe, but struggles on smaller scales where baryonic physics can dominate.  In particular, two 'problems' with the CDM paradigm have been identified: 1) the observed deficit in the number of low mass satellites around the Milky Way and 2) the flat, cored inner dark matter density profiles seen in some galaxy and cluster centers, contrary to the universally 'cuspy' halos seen in simulations.  While these 'problems' are not likely to be the death knell of CDM, they do represent an opportunity to study how baryonic physics effect the distribution of dark matter.

I will discuss two observational programs aimed at better understanding the two 'problems' associated with CDM.  First, I will present measurements of the dark matter density profile in galaxy clusters utilizing a combination of gravitational lensing and galaxy dynamics to measure the mass at different scales.  Additionally, I will present results from our imaging survey to measure the structure and star formation history of the newly discovered ultrafaint Milky Way satellites, a prerequisite for understanding how stars populate the smallest dark matter halos. In both cases, I will lay out immediate and longer term plans for observationally characterizing the relationship between dark matter and baryons.