Discovery of a Premerger Shock in an Intercluster Filament in Abell 98

Sarkar, Arnab; Randall, Scott W.; Su, Yuanyuan; Alvarez, Gabriella E.; Sarazin, Craig L.; Nulsen, P. E. J.; Blanton, E. L.; Forman, W.; Jones, Christine; Bülbül, Esra; ZuHone, John; Andrade-Santos, Felipe; Johnson, Ryan; Chakraborty, Priyanka

doi:10.3847/2041-8213/ac86d4

Cited by 12 publications

(20 citation statements)

References 43 publications

(79 reference statements)

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“…This study also determined that A98S has an asymmetric ICM distribution, indicating that A98S is still undergoing a major merger. Sarkar et al (2022) found definitive evidence of a shocked edge to the south of A98N with deeper Chandra observations, confirming that A98N and A98S are likely in the early stages of a merging event.…”

Section: Introductionsupporting

confidence: 59%

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

Alvarez

Randall

et al. 2022

ApJ

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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.

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Section: Introductionsupporting

confidence: 59%

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

Alvarez

Randall

et al. 2022

ApJ

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“…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).…”

Section: Imaging Analysismentioning

confidence: 64%

“…α 1 and α 2 are the slopes inside and outside the edge, respectively. We project the estimated emission measure profile onto the sky plane and fit the observed surface brightness profile by varying the slopes, edge radius, and the magnitude of the jump (similar to what we did for the shock front in paper I; Sarkar et al 2022). Figure 3 displays the bestfit models (red) and the 3D density profiles (inset) for both directions.…”

Section: A98nmentioning

confidence: 97%

“…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.…”

mentioning

confidence: 98%

“…A98N is a cool core cluster with an asymmetric warmer gas arc in the south (Paterno-Mahler et al 2014). In paper I (Sarkar et al 2022), we investigated this scenario in detail. We reported a shock front with a Mach number of M ≈ 2.3 at about 420 kpc south from the A98N core.…”

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confidence: 99%

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

Sarkar¹,

Randall²,

Su³

et al. 2022

Preprint

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We present deep Chandra observations of the pre-merger galaxy cluster Abell 98. Abell 98 is a complex merging system. While the northern (A98N) and central subclusters (A98S) are merging along the north-south direction, A98S is undergoing a separate late-stage merger, with two distinct X-ray cores. We report detection of gas sloshing spirals in A98N and in the eastern core of A98S. We detect two cold front edges in A98N. We find two more surface brightness edges along the east direction of the eastern core and west direction of the western core of A98S. We measure the temperatures and gas densities across those edges, and find that the eastern edge appears to be a cold front while the western edge is a shock front with a Mach number of M ≈ 1.5. We detect a "tail" of X-ray emission associated with the eastern core of A98S. Our measurement indicates that the tail is cooler than the surrounding gas at a 4.2-σ level, suggesting the tail is part of a cool core remnant that has been ram-pressure stripped.

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The eROSITA view of the Abell 3391/95 field

Veronica,

Reiprich,

Pacaud

et al. 2024

A&A

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About $30<!PCT!>-40<!PCT!>$ of the baryons in the local Universe remain unobserved. Many of these "missing" baryons are expected to reside in the warm-hot intergalactic medium (WHIM) of the cosmic web filaments that connect clusters of galaxies. SRG/eROSITA performance verification (PV) observations covered about 15 square degrees of the A3391/95 system and have revealed a sim 15 Mpc continuous soft emission connecting several galaxy groups and clusters. We aim to characterize the gas properties in the cluster outskirts ($R_ <r<R_ $) and in the detected inter-cluster filaments ($>R_ $) and to compare them to predictions. We performed X-ray image and spectral analyses using the eROSITA PV data in order to assess the gas morphology and properties in the outskirts and the filaments in the directions of the previously detected Northern and Southern Filament of the A3391/95 system. We constructed surface brightness profiles using particle-induced background-subtracted, exposure- and Galactic absorption-corrected eROSITA products in the soft band ($0.3-2.0 keV $). We constrained the temperatures, metallicities, and electron densities through X-ray spectral fitting and compared them with the expected properties of the WHIM. We took particular care of the foreground. In the filament-facing outskirts of A3391 and the Northern Clump, we find higher temperatures than typical cluster outskirts profiles, with a significance of between 1.6 and $2.8 suggesting heating due to their connections with the filaments. We confirm surface brightness excess in the profiles of the Northern, Eastern, and Southern Filaments. From spectral analysis, we detect hot gas of keV $ and $1.09_ keV $ for the Northern and Southern Filament, respectively, which are close to the upper WHIM temperature limit. The filament metallicities are below 10<!PCT!> solar metallicity and the electron densities are ranging between $2.6$ and $6.3 cm^ $. The characteristic properties of the Little Southern Clump (LSC), which is located at a distance of $ $ from A3395S in the Southern Filament, suggest that it is a small galaxy group. Excluding the LSC from the analysis of the Southern Filament does not significantly change the temperature or metallicity of the gas, but it decreases the gas density by 30<!PCT!>. This shows the importance of taking into account any clumps in order to avoid overestimation of the gas measurement in the outskirts and filament regions. We present measurements of morphology, temperature, metallicity, and density of individual warm-hot filaments. The electron densities of the filaments are consistent with the WHIM properties as predicted by cosmological simulations, but the temperatures are higher. As both filaments are short (1.8 and 2.7 Mpc) and located in a denser environment, stronger gravitational heating may be responsible for this temperature enhancement. The metallicities are low, but still within the expected range from the simulations.

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Discovery of a Premerger Shock in an Intercluster Filament in Abell 98

Cited by 12 publications

References 43 publications

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

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

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

The eROSITA view of the Abell 3391/95 field

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