"The Density Profiles of Galaxy Clusters Over 3 Decades in Radius"

 

ABSTRACT:

The density profile of halos composed purely of cold dark matter (CDM) is precisely predicted in numerical simulations. Observations of real systems ranging from dwarf galaxies to galaxy clusters have suggested deviations from this form on small scales. This could reflect the role of baryons in the formation of these systems, or alternatively mayinform us about the dark matter particle.

 

I will present observations of 7 massive, relaxed clusters at z~0.2-0.3 using the techniques of strong and weak gravitational lensing, coupled with spatially-resolved stellar kinematics within the centrally-located brightest cluster galaxies (BCGs). Combining these high-quality data yields precise constraints on the density profile from ~3 kpc to 3 Mpc. At radii >~5-10 kpc, we find that the total density profiles (dark and baryonic) agree surprisingly well with state-of-the-art cluster simulations containing only CDM, despite the significant contribution of stars in the BCG on these scales.

 

I will show how stellar kinematic data at small radii can be used to separate stellar and dark mass and isolate the inner dark matter density profiles. These are found to be shallow compared to CDM cusps and correlate with the properties of the BCG. I will discuss physical explanations proposed to account for this.