Suzaku Observations of the Cluster Outskirts and Intercluster Filament in the Triple Merger Cluster A98

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 ≈ 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 that are expected for the warm–hot intergalactic medium ( kT = 0.11 − 0.02 + 0.01 keV and n e = 7.6 × 10−5 ± 3.6 × 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 2.2σ level, as well as a tentative detection of cool gas (kT ∼ 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.

Gas Sloshing and Cold Fronts in Pre-merging Galaxy Cluster A98

“…Figure 1 shows a slightly smoothed image of A98N (northern subcluster) and A98S (central subcluster) in the 0.5-2 keV band, obtained after co-adding all 10 observations and by applying the correction for exposure nonuniformity. As reported by earlier studies, the cluster is an early-stage merger, with the merger axis likely aligned along a local north-south (N-S) large-scale filament connecting A98N and A98S (e.g., Paterno-Mahler et al 2014;Alvarez et al 2022;Sarkar et al 2022).…”

“…(e.g., Alvarez et al 2022;Sarkar et al 2022). Alvarez et al (2022) also reported a filament extending to the north beyond A98N, indicating A98N and A98S lie along a large-scale cosmic filament. In this work, we focus on the northern and central subclusters.…”

“…Previous studies have reported a shock front associated with the northern subcluster and a filament connecting the northern and central subclusters. (e.g., Alvarez et al 2022;Sarkar et al 2022). Alvarez et al (2022) also reported a filament extending to the north beyond A98N, indicating A98N and A98S lie along a large-scale cosmic filament.…”

Gas sloshing and cold fronts in pre-merging galaxy cluster Abell 98

“…Figure 1 shows a slightly smoothed image of A98N (northern sub-cluster) and A98S (central sub-cluster) in the 0.5-2 keV band, obtained after co-adding all ten observations and by applying the correction for exposure non-uniformity. As reported by earlier studies, the cluster is an early-stage merger, with the merger axis likely aligned along a local N-S large-scale filament connecting A98N and A98S (e.g., Paterno-Mahler et al 2014;Alvarez et al 2022;Sarkar et al 2022).…”

“…Previous studies have reported a shock front associated with the northern sub-cluster and a filament connecting the northern and central sub-clusters. (e.g., Alvarez et al 2022;Sarkar et al 2022). Alvarez et al (2022) also reported a filament extending to the north beyond A98N, indicating A98N and A98S lie along a large-scale cosmic filament.…”