The importance of the merging activity for the kinetic polarization of the Sunyaev-Zel'dovich signal from galaxy clusters

TL;DR

This paper investigates how the internal dynamics and physical modeling of galaxy clusters influence the kinetic polarization signal (kpSZ), which is crucial for future cosmological studies using polarization data from galaxy clusters.

Contribution

It provides a detailed analysis of the kpSZ signal's dependence on cluster dynamics and baryonic physics using high-resolution hydrodynamical simulations, highlighting the impact of mergers and modeling choices.

Findings

Major mergers amplify the kpSZ signal up to tenfold.

Relaxed clusters show significantly lower kpSZ amplitudes.

Physical modeling affects the inner regions of clusters only.

Abstract

The polarization sensitivity of the upcoming millimetric observatories will open new possibilities for studying the properties of galaxy clusters and for using them as powerful cosmological probes. For this reason it is necessary to investigate in detail the characteristics of the polarization signals produced by their highly ionized intra-cluster medium (ICM). This work is focussed on the polarization effect induced by the ICM bulk motions, the so-called kpSZ signal, which has an amplitude proportional to the optical depth and to the square of the tangential velocity. In particular we study how this polarization signal is affected by the internal dynamics of galaxy clusters and what is its dependence on the physical modelling adopted to describe the baryonic component. This is done by producing realistic kpSZ maps starting from the outputs of two different sets of high-resolution hydrodynamical N-body simulations. The first set (17 objects) follows only non-radiative hydrodynamics, while for each of 9 objects of the second set we implement four different kinds of physical processes. Our results shows that the kpSZ signal turns out to be a very sensitive probe of the dynamical status of galaxy clusters. We find that major merger events can amplify the signal up to one order of magnitude with respect to relaxed clusters, reaching amplitude up to about 100 nuK. This result implies that the internal ICM dynamics must be taken into account when evaluating this signal because simplicistic models, based on spherical rigid bodies, may provide wrong estimates. Finally we find that the dependence on the physical modelling of the baryonic component is relevant only in the very inner regions of clusters.