Weighing Galaxy Clusters with Gas. I. On the Methods of Computing Hydrostatic Mass Bias

Understand

Mass estimates of galaxy clusters from X-ray and Sunyeav-Zel'dovich observations assume the intracluster gas is in hydrostatic equilibrium with their gravitational potential.

• However, since galaxy clusters are dynamically active objects whose dynamical states can deviate significantly from the equilibrium configuration, the departure from the hydrostatic equilibrium assumption is one of the largest sources of systematic uncertainties in cluster cosmology.
• In the literature there has been two methods for computing the hydrostatic mass bias based on the Euler and the modified Jeans equations, respectively, and there has been some confusion about the validity of these two methods.
• The word "Jeans" was a misnomer, which incorrectly implies that the gas is collisionless.