THE INTRACLUSTER PLASMA: A UNIVERSAL PRESSURE PROFILE?

The pressure profiles of the intracluster plasma in galaxy clusters show a wide variance when observed in X-rays at low redshifts, z less than or similar to 0.2. We find the profiles to follow two main patterns, featuring either a steep or a shallow shape throughout both core and outskirts. We trace these shapes back to a physical dichotomy of clusters into two classes, marked by either low entropy (LE) or high entropy (HE) throughout. From X-ray observations and Sunyaev-Zel'dovich (SZ) stacked data at higher redshifts 0.2 less than or similar to z less than or similar to 0.4, we obtain evidence of an increasing abundance of HEs relative to LEs. We propose this to constitute a systematic trend toward high z; specifically, we predict the pressure profiles to converge into a truly universal HE-like template for z greater than or similar to 0.5. We submit our physical templates and converging trend for further observational tests, in view of current and upcoming measurements of individual, stacked, and integrated SZ signals.