Multi-frequency Radio Observations of the Dissociative Cluster Merger CIZA J0107.7+5408

TL;DR

This study presents multi-frequency radio observations of the galaxy cluster CIZA J0107.7+5408, revealing complex diffuse radio emissions, spectral index variations, and possible shock interactions, advancing understanding of cluster merger dynamics.

Contribution

The paper provides detailed radio imaging and spectral analysis of CIZA J0107.7+5408, highlighting the presence of steep-spectrum regions, ultra-steep features, and shock-related edges, offering new insights into merger-related radio phenomena.

Findings

Detection of steep-spectrum radio emission (~-1.3) in subclusters.

Identification of ultra-steep spectrum regions (<-2) superimposed on larger emission.

Observation of a radio edge coincident with a weak shock in X-ray data.

Abstract

We present new radio observations of the galaxy cluster merger CIZA J0107.7+5408 (CIZA0107), a large, roughly equal mass, post-core passage, dissociative binary system at z = 0.1066. CIZA0107 is an elongated, disturbed system, hosting two subclusters with optical galaxy number density peaks offset from their associated X-ray density peaks and double-peaked diffuse radio structure. We present new 240-470 MHz and 2.0-4.0 GHz Very Large Array observations of CIZA0107. We image the diffuse emission at high resolution, constrain its integrated spectrum, and map the spectral index distribution. We confirm the presence of steep-spectrum ($\alpha$ $\sim$ -1.3) emission on a scale of about 0.5 Mpc in both subclusters. We identify two smaller ultra-steep spectrum ($\alpha$ $<$ -2) regions, superimposed on larger-scale radio emission associated with the southwestern subcluster. At 340 MHz, we detect a radio edge bounding the emission to the south and show that it is coincident with a weak (M $\sim$ 1.2) shock identified in the Chandra image. At 3 GHz, the emission does not show any corresponding edge-like feature, and in fact it extends beyond the shock. We investigate the nature of the emission in CIZA0107 and find that, while the system may host a double halo structure, we cannot rule out a scenario in which the emission arises from two relics projected on the central cluster regions.