On Escaping a Galaxy Cluster in an Accelerating Universe

TL;DR

This paper derives and tests an escape velocity profile for galaxy clusters in an accelerating universe, showing the importance of cosmology-dependent terms and potential as a new cosmological probe.

Contribution

It introduces a new analytic model for escape velocity profiles that incorporates universe acceleration and validates it with simulations and observational data.

Findings

Theoretical profile including acceleration matches simulation data.

Inferred velocity anisotropy significantly differs when ignoring acceleration.

Archival data constrains cluster velocity anisotropy with reasonable confidence.

Abstract

We derive the escape velocity profile for an Einasto density field in an accelerating universe and demonstrate its physical viability by comparing theoretical expectations to both light-cone data generated from N-body simulations and archival data on 20 galaxy clusters. We demonstrate that the projection function ($g(\beta )$) is deemed physically viable only for the theoretical expectation that includes a cosmology-dependent term. Using simulations, we show that the inferred velocity anisotropy is more than 6{\sigma} away from the expected value for the theoretical profile that ignores the acceleration of the universe. In the archival data, we constrain the average velocity anisotropy parameter of a sample of 20 clusters to be $\beta ={0.248}_{-0.360}^{+0.164}$ at the 68% confidence level. Lastly, we briefly discuss how our analytic model may be used as a novel cosmological probe based on galaxy clusters.