Mass Estimation of Merging Galaxy Clusters

TL;DR

This study examines how galaxy cluster mergers affect mass estimates derived from simulations, revealing dependencies on merger dynamics and observational perspectives, and compares virial and X-ray based methods.

Contribution

It provides a detailed analysis of mass estimation biases during cluster mergers using simulations, highlighting the influence of observational direction and method choice.

Findings

Virial mass can be over twice the real mass during mergers.

X-ray mass estimates are generally more accurate than virial estimates.

Projection effects cause underestimation of mass along the collision axis.

Abstract

We investigate the impact of mergers on the mass estimation of galaxy clusters using $N$-body + hydrodynamical simulation data. We estimate virial mass from these data and compare it with real mass. When the smaller subcluster's mass is larger than a quarter of that of the larger one, virial mass can be larger than twice of the real mass. The results strongly depend on the observational directions, because of anisotropic velocity distribution of the member galaxies. We also make the X-ray surface brightness and spectroscopic-like temperature maps from the simulation data. The mass profile is estimated from these data on the assumption of hydrostatic equilibrium. In general, mass estimation with X-ray data gives us better results than virial mass estimation. The dependence upon observational directions is weaker than in case of virial mass estimation. When the system is observed along the collision axis, the projected mass tends to be underestimated. This fact should be noted especially when the virial and/or X-ray mass are compared with gravitational lensing results.