Probing the Curious Case of a Galaxy Cluster Merger in Abell 115 with High-fidelity Chandra X-Ray Temperature and Radio Maps

Abstract

We present results from an X-ray and radio study of the merging galaxy cluster Abell 115. We use the full set of 5 Chandra observations taken of A115 to date (360 ks total integration) to construct high-fidelity temperature and surface brightness maps. We also examine radio data from the Very Large Array at 1.5 GHz and the Giant Metrewave Radio Telescope at 0.6 GHz. We propose that the high X-ray spectral temperature between the subclusters results from the interaction of the bow shocks driven into the intracluster medium by the motion of the subclusters relative to one another. We have identified morphologically similar scenarios in Enzo numerical N-body/hydrodynamic simulations of galaxy clusters in a cosmological context. In addition, the giant radio relic feature in A115, with an arc-like structure and a relatively flat spectral index, is likely consistent with other shock-associated giant radio relics seen in other massive galaxy clusters. We suggest a dynamical scenario that is consistent with the structure of the X-ray gas, the hot region between the clusters, and the radio relic feature.

Diffuse Radio Emission from Galaxy Clusters

“…Magnetic fields permeate galaxy clusters and the intergalactic medium on Mpc-scales. These fields play key roles in particle acceleration and on the process of large scale structure forma- Goss et al (1987), Subrahmanyan et al (2003) Perseus cluster 0.018 Miley and Perola (1975), Noordam and de Bruyn (1982) Pedlar et al (1990, Burns et al (1992), Sijbring (1993) Sijbring and de Bruyn (1998), Brentjens 2011Gendron-Marsolais et al 2017Abell 1367 0.022 Gavazzi (1978), Hanisch (1980, Ballarati et al (1981) Gavazzi andTrinchieri (1983), Gavazzi andJaffe (1987) Farnsworth et al (2013) Coma cluster a 0.023 H, RS Large et al (1959), Willson (1970), Jaffe andRudnick (1979) Ballarati et al (1981), Andernach et al (1984) Giovannini et al (1985, Schlickeiser et al (1987) Giovannini et al (1991…”

Multiwavelength Analysis of the Merging Galaxy Cluster A115

“…Point 1 is strong evidence that the system is post merger. Although Hallman et al (2018) suggests a possibility that the radio relic might be a pre-merger shock, our numerical simulation with our WL masses as input shows that this shock would be too weak to generate such a giant radio relic even if there exists a rich population of so-called fossil electrons (Lee et al in prep). The last point supports the possibility that the merger is taking place nearly in the plane of the sky.…”

The galaxy cluster ‘Pypeline’ for X-ray temperature maps: ClusterPyXT

“…While this aspect of calculating the temperature is standard 5 , the way the maps are binned is not. Recent findings regarding A2256, the "Toothbrush" cluster [18], and A115 [15] to name a few, all have featured X-ray temperature maps using a variety of low-resolution binning methods. Our recent work on A115 indicates that high-resolution temperature maps can reveal heretofore unidentified X-ray features that are critical to interpreting the dynamics of merging galaxy clusters [15].…”

“…Recent findings regarding A2256, the "Toothbrush" cluster [18], and A115 [15] to name a few, all have featured X-ray temperature maps using a variety of low-resolution binning methods. Our recent work on A115 indicates that high-resolution temperature maps can reveal heretofore unidentified X-ray features that are critical to interpreting the dynamics of merging galaxy clusters [15]. ClusterPyXT uses an adaptive circular binning (ACB) [19,20,21,22] to create a bin for each pixel.…”