Project Title:Sloshing of Cool Gas in the Cores of Relaxed Galaxy Clusters

Project Advisor: Dr. Maxim Markevitch

Background: The very first high-resolution Chandra X-ray images of galaxy clusters revealed what we now call "cold fronts" - sharp contact discontinuities delineating large clouds of cool, dense gas flying through less dense, hotter gas. Most clusters have them - even those we thought were perfectly at rest, based on lower-resolution data. In these latter ones, cold fronts are found in the cluster's cool central regions (formerly known as cooling flows), and we think they indicate "sloshing" of the low-entropy gas at the bottom of the gravitational potential well.

Scientific Questions: Do all clusters with cool cores have their central cool gas out of hydrostatic equilibrium? What is the distribution of velocities of this gas? Can anything be said about the nature and frequency of the disturbing events that set off this sloshing? Are total masses of cluster cores systematically underestimated because of gas sloshing?

Scientific Methodology: The project will involve analysis of the vast archive of Chandra observations of clusters with cool cores. From the brightness edges in the cluster X-ray images, we will derive the amplitude of the gas density jump, and from the spectra, the gas temperatures. The question of mass underestimates will be addressed by the analysis of the (existing) hydrodynamic simulations of cold fronts in the cluster cores (Ascasibar and Markevitch 2006).

Other links related to this project:

• Shocks and cold fronts in galaxy clusters; M. Markevitch and A. Vikhlinin 2007, Phys. Reports, 443, 1