Spectral and morphological signatures of cluster merger shocks: CIZA J2242.8+5301

TL;DR

This study investigates the spectral and morphological features of shock waves in the galaxy cluster CIZA J2242.8+5301, revealing spectral aging, spectrum curvature challenges, and increased galaxy activity possibly due to shock interactions.

Contribution

It provides new multi-wavelength observations showing spectral steepening, curvature, and galaxy activity enhancement linked to cluster merger shocks.

Findings

Spectral steepening and curvature indicate electron aging.

The spectrum curvature at 16 GHz challenges existing relic models.

Hα emitter density increases by a factor of 10 near shocks.

Abstract

The CIZA J2242.8+5301 cluster hosts an extraordinary, narrow, Mpc-wide, diffuse patch of radio emission tracing travelling shock waves, called a relic. We perform a multi-wavelength of observations of the cluster. We discover radio spectral steepening and increasing spectral curvature in the shock downstream area, indicative of emission produced by spectrally-aged electrons, following a JP ageing model. The curved integrated spectrum towards $16$ GHz challenges the favoured relic formation model. Further, we find a boosting the number density of H$\alpha$ emitters by a factor of $10$, possibly caused by interactions of the galaxies with the shock wave.