Simulating the galaxy cluster "El Gordo": gas motion, kinetic Sunyaev-Zel'dovich signal, and X-ray line features

TL;DR

This paper uses numerical simulations to predict the kinetic Sunyaev-Zel'dovich effect, relativistic tSZ correction, and X-ray spectral features of the galaxy cluster 'El Gordo' under different merger models, aiding future observational constraints.

Contribution

It introduces detailed predictions of SZ and X-ray signals for two merger scenarios of 'El Gordo', linking gas dynamics to observable features for the first time.

Findings

kSZ amplitude is ~10^-5 with different morphologies for each model

Relativistic tSZ correction at 240 GHz can constrain electron temperature

X-ray line shifts and broadening differ significantly between models

Abstract

The massive galaxy cluster "El Gordo" (ACT-CL J0102--4915) is a rare merging system with a high collision speed suggested by multi-wavelength observations and the theoretical modeling. Zhang et al. (2015) propose two types of mergers, a nearly head-on merger and an off-axis merger with a large impact parameter, to reproduce most of the observational features of the cluster, by using numerical simulations. The different merger configurations of the two models result in different gas motion in the simulated clusters. In this paper, we predict the kinetic Sunyaev-Zel'dovich (kSZ) effect, the relativistic correction of the thermal Sunyaev-Zel'dovich (tSZ) effect, and the X-ray spectrum of this cluster, based on the two proposed models. We find that (1) the amplitudes of the kSZ effect resulting from the two models are both on the order of $\Delta T/T\sim10^{-5}$; but their morphologies are different, which trace the different line-of-sight velocity distributions of the systems; (2) the relativistic correction of the tSZ effect around $240 {\rm\,GHz}$ can be possibly used to constrain the temperature of the hot electrons heated by the shocks; and (3) the shift between the X-ray spectral lines emitted from different regions of the cluster can be significantly different in the two models. The shift and the line broadening can be up to $\sim 25{\rm\,eV}$ and $50{\rm\,eV}$, respectively. We expect that future observations of the kSZ effect and the X-ray spectral lines (e.g., by ALMA, XARM) will provide a strong constraint on the gas motion and the merger configuration of ACT-CL J0102--4915.