Suzaku Observations of the Cluster Outskirts and Intercluster Filament in the Triple Merger Cluster Abell 98

TL;DR

This study uses Suzaku X-ray observations to analyze the outskirts of the Abell 98 galaxy cluster system, revealing structures consistent with the warm-hot intergalactic medium and large-scale cosmic filaments, and providing insights into cluster merger geometry.

Contribution

First detailed Suzaku analysis of Abell 98's outskirts, identifying filamentary structures and the WHIM, and inferring the cluster's orientation relative to the line of sight.

Findings

Detection of WHIM-like emission beyond r200 along the merger axis.

Evidence of filamentary emission between clusters at 2.2σ significance.

Indications that the system is aligned closer to the plane of the sky.

Abstract

We present Suzaku observations of the Abell 98 (A98) triple galaxy cluster system and the purported intercluster filament. The three subclusters are expected to lie along a large scale cosmic filament. With partial azimuthal coverage of the northernmost cluster, we find that the inferred entropy profile of this relatively low mass cluster ($kT \approx 2.8$ keV) adheres to expectations from models of self-similar pure gravitational collapse in the region of the virial radius. There is evidence of extended structure beyond $r_{200}$ to the north of the northernmost cluster, along the merger axis, with properties consistent with what is expected for the warm-hot intergalacitc medium (WHIM; $kT = 0.11_{-0.02}^{+0.01}$ keV, $n_e = {7.6 \times 10^{-5}}^{+3.6 \times 10^{-5}}_{-3.6 \times 10^{-5}}$~cm$^{-3}$). No such emission is detected at the same radius in regions away from the merger axis, consistent with the expectation that the merger axis of this triple system lies along a large scale cosmic filament. In the bridge region between A98N and A98S, there is evidence of filamentary emission at the $2.2\sigma$ level, as well as a tentative detection of cool gas ($kT \sim 1$ keV). The entropy profile of this intercluster filament suggests that the A98 system is most likely aligned closer to the plane of the sky rather than along the line of sight. The structure to the north of the system, as well as in between A98N and A98S is indicative that the clusters are connected to a larger-scale structure spanning at least 4 Mpc.