The eROSITA view of the Abell 3391/95 field: The Northern Clump

Veronica, A.; Su, Yuanyuan; Biffi, V.; Reiprich, T. H.; Pacaud, F.; Nulsen, Paul; Kraft, Ralph; Sanders, Jeremy; Bogdán, Ákos; Kára, M.; Dolag, K.; Kerp, J.; Koribalski, B. S.; Erben, T.; Bülbül, Esra; Gatuzz, E.; Ghirardini, Vittorio; Hopkins, A. M.; Liu, Ang; Migkas, K.; Vernstrom, Tessa

doi:10.1051/0004-6361/202141415

Cited by 12 publications

(8 citation statements)

References 68 publications

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“…Dolag et al 2006). The configuration of group B roughly ∼3 Gyr ago and the whole picture shown since then, that is, between z ∼ 0.25 and z ∼ 0.16, is consistent with the properties of the observed Northern Clump in the eROSITA A3391/95 field (Veronica et al 2022), which is located at a similar projected distance of about three virial radii from the A3391 cluster (Reiprich et al 2021;Veronica et al 2022).…”

Section: Additional Structures In the Local Environmentsupporting

confidence: 77%

“…While entering the outer atmosphere of GC1 (z 0.16), it undergoes gas stripping, as marked by the decrease in bound gas mass by a factor ∼3. The configuration corresponding to 3 Gyr ago (z ∼ 0.25) shares several similarities with the case of the real Northern Clump relative to A3391, supporting the picture of its actual infalling motion towards the A3391/95 system (see Veronica et al 2022). The eROSITA superior soft response and large FoV has allowed the first direct detection of the faint X-ray emission from the diffuse gas in the bridge and filaments connected to A3391/95, drawing a consistent picture of the LSS that compares well to theoretical predictions.…”

Section: Discussionsupporting

confidence: 64%

“…However, group B showed a configuration similar to that of the Northern Clump about ∼3 Gyr ago (z ∼ 0.25), when it was at a distance of ∼3 × R 200 from GC1. We used this example to speculate that the features presented by the Northern Clump in the eROSITA observations are consistent with a radial motion of the system towards A3391 and the pair (Veronica et al 2022). From the evolution of group B between z ∼ 0.25 and the final snapshot (z = 0.07), we observe a slowing down of the gas compared to DM, and a stripping of the gas in the later merging stages (z 0.16) when group B finally enters the virial boundary of GC1.…”

Section: Discussionmentioning

confidence: 96%

“…In the eROSITA A3391/95 field, the Northern Clump (MCXC J0621.7-5242) cluster located in the Northern Filament in particular shows several pieces of evidence that suggest a motion towards the A3391 cluster and a possible interaction with the filament gas in which it is embedded. These comprise, for instance, an emission enhancement towards the south, a tail of emission extending towards the north, and a pair of bent asymmetric radio lobes of its central wide-angle tails (WAT) radio galaxy as well (Brüggen et al 2021;Veronica et al 2022). We therefore investigated and compared the signatures of the movement of groups A and B towards the galaxy cluster pair at redshift z 1.…”

Section: Additional Structures In the Local Environmentmentioning

confidence: 99%

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The eROSITA view of the Abell 3391/95 field: Case study from the Magneticum cosmological simulation

Biffi

Dolag

Reiprich

et al. 2022

A&A

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Context. Clusters of galaxies reside at the nodes of the cosmic web, interconnected by filamentary structures that contain tenuous diffuse gas, especially in the warm-hot phase. Galaxy clusters grow by mergers of smaller objects and gas that are mainly accreted through these large-scale filaments. For the first time, the large-scale cosmic structure and a long gas-emission filament have been captured by eROSITA on board the Spectrum-Roentgen-Gamma mission in a direct X-ray observation of the A3391/95 field. Aims. We investigate the assembly history of an A3391/95-like system of clusters and the thermo-chemical properties of the diffuse gas in it by connecting simulation predictions to the eROSITA observations with the aim to constrain the origin and nature of the gas in the pair-interconnecting bridge. Methods. We analysed the properties of a system resembling A3391/95, extracted from the (352 h−1 cMpc)3 volume of the Magneticum Pathfinder cosmological simulations at z = 0.07. We tracked the main progenitors of the pair clusters and of surrounding groups back in time to study the assembly history of the system and its evolution. Results. Similarly to the observed A3391/95 system, the simulated cluster pair is embedded in a complex network of gas filaments, with structures aligned over more than 20 projected Mpc, and the whole region collapses towards the central overdense node. The spheres of influence (3 × R200) of the two main clusters already overlap at z = 0.07, but their virial boundaries are still physically separated. The diffuse gas located in the interconnecting bridge closely reflects the warm-hot intergalactic medium, with a typical temperature of ~1 keV and an overdensity δ ~ 100 with respect to the mean baryon density of the Universe, and a lower enrichment level compared to the intra-cluster medium in clusters. We find that most of the bridge gas collapsed from directions roughly orthogonal to the intra-cluster gas accretion directions, and its origin is mostly unrelated to the two cluster progenitors. We find clear signatures in the surrounding groups of infall motion towards the pair, such as significant radial velocities and a slowdown of gas compared to dark matter. These findings further support the hypothesis that the Northern Clump (MCXC J0621.7-5242) cluster infalls along a cosmic gas filament towards Abell 3391 and might be merging with it. Conclusions. We conclude that in this configuration, the pair clusters of the A3391/95-like system are in a pre-merger phase and have not yet interacted. The diffuse gas in the interconnecting bridge is mostly warm filament gas and not tidally stripped cluster gas.

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Section: Additional Structures In the Local Environmentsupporting

confidence: 77%

Section: Discussionsupporting

confidence: 64%

Section: Discussionmentioning

confidence: 96%

Section: Additional Structures In the Local Environmentmentioning

confidence: 99%

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The eROSITA view of the Abell 3391/95 field: Case study from the Magneticum cosmological simulation

Biffi

Dolag

Reiprich

et al. 2022

A&A

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“…Furthermore, if an emission bridge does connect the two clusters, the eRASS image will provide its observation. More generally, given the early eROSITA results on cluster outskirts and infall regions (e.g., Reiprich et al 2021;Ghirardini et al 2021;Churazov et al 2021;Veronica et al 2022;Whelan et al 2021;Sanders et al 2022), and given the close correspondence to similar structures observed in cosmological hydrodynamical simulations (e.g., Biffi et al 2022), we may expect that bridges and clumpy filaments will be discovered in several more nearby systems in the future in the eRASS. These systems can then be studied in detail after the eight surveys are completed using the SRG/eROSITA scanning mode, with which areas of tens of square degrees can be scanned efficiently, homogeneously, and deeply.…”

Section: Discussionmentioning

confidence: 72%

eROSITA spectro-imaging analysis of the Abell 3408 galaxy cluster

Iljenkarevic

Reiprich

Pacaud

et al. 2022

A&A

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Context. The X-ray telescope eROSITA on board the newly launched Spectrum-Roentgen-Gamma (SRG) mission serendipitously observed the galaxy cluster Abell 3408 (A3408) during the performance verification observation of the active galactic nucleus 1H 0707–495. The field of view of eROSITA is one degree, which allowed us to trace the intriguing elongated morphology of the nearby (z = 0.0420) A3408 cluster. Despite its brightness (F500 ≈ 7 × 10−12 ergs s−1 cm−2) and large extent (r200 ≈ 21'), it has not been observed by any modern X-ray observatory in over 20 yr. A neighboring cluster in the NW direction, A3407 (r200 ≈ 18', z = 0.0428), appears to be close at least in projection (~1.7 Mpc). This cluster pair might be in a pre- or post-merger state. Aims. We aim to determine the detailed thermodynamical properties of this special cluster system for the first time. Furthermore, we aim to determine which of the previously suggested merger scenarios (pre- or post-merger) is preferred. Methods. We performed a detailed X-ray spectro-imaging analysis of A3408. We constructed particle-background-subtracted and exposure-corrected images and surface brightness profiles in different sectors. The spectral analysis was performed out to 1.4r500 and included normalization, temperature, and metallicity profiles determined from elliptical annuli aligned with the elongation of A3408. Additionally, a temperature map is presented that depicts the distribution of the intracluster medium (ICM) temperature. Furthermore, we make use of data from the ROSAT all-sky survey to estimate some bulk properties of A3408 and A3407, using the growth-curve analysis method and scaling relations. Results. The imaging analysis shows the complex morphology of A3408 with a strong elongation in the SE-NW direction. This is quantified by comparing the surface brightness profiles of the NW, SW, SE, and NE directions, where the NW and SE directions show a significantly higher surface brightness than the other directions. We determine a gas temperature kBr500 = (2.23 ± 0.09) keV in the range 0.2r500 to 0.5r500 from the spectral analysis. The temperature profile reveals a hot core within two arcminutes of the emission peak, ${k_{\rm{B}}}T = 3.04_{- 0.25}^{+ 0.29}$ keV. Employing a mass–temperature relation, we obtain M500 = (9.27 ± 0.75) × 1013M⊙ iteratively. The r200 of A3407 and A3408 are found to overlap in projection, which makes ongoing interactions plausible. The two-dimensional temperature map reveals higher temperatures in the W than in the E direction. Conclusions. The elliptical morphology together with the temperature distribution suggests that A3408 is an unrelaxed system. The system A3407 and A3408 is likely in a pre-merger state, with some interactions already affecting the ICM thermodynamical properties. In particular, increased temperatures in the direction of A3407 indicate adiabatic compression or shocks due to the starting interaction.

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The eROSITA Final Equatorial-Depth Survey (eFEDS)

Bahar

Bülbül

Clerc

et al. 2022

A&A

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Context. Scaling relations link the physical properties of clusters at cosmic scales. They are used to probe the evolution of large-scale structure, estimate observables of clusters, and constrain cosmological parameters through cluster counts. Aims. We investigate the scaling relations between X-ray observables of the clusters detected in the eFEDS field using Spectrum-Roentgen-Gamma/eROSITA observations taking into account the selection effects and the distributions of observables with cosmic time. Methods. We extract X-ray observables (LX, Lbol, T, Mgas, YX) within R500 for the sample of 542 clusters in the eFEDS field. By applying detection and extent likelihood cuts, we construct a subsample of 265 clusters with a contamination level of <10% (including AGNs and spurious fluctuations) to be used in our scaling relations analysis. The selection function based on the state-of-the-art simulations of the eROSITA sky is fully accounted for in our work. Results. We provide the X-ray observables in the core-included <R500 and core-excised 0.15 R500-R500 apertures for 542 galaxy clusters and groups detected in the eFEDS field. Additionally, we present our best-fit results for the normalization, slope, redshift evolution, and intrinsic scatter parameters of the X-ray scaling relations between LX - T, LX - Mgas, LX - YX, Lbol - T, Lbol - Mgas, Lbol - YX, and Mgas - T. We find that the best-fit slopes significantly deviate from the self-similar model at a >4σ confidence level, but our results are nevertheless in good agreement with the simulations including non-gravitational physics, and the recent results that take into account selection effects. Conclusions. The strong deviations we find from the self-similar scenario indicate that the non-gravitational effects play an important role in shaping the observed physical state of clusters. This work extends the scaling relations to the low-mass, low-luminosity galaxy cluster and group regime using eFEDS observations, demonstrating the ability of eROSITA to measure emission from the intracluster medium out to R500 with survey-depth exposures and constrain the scaling relations in a wide mass-luminosity-redshift range.

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The eROSITA view of the Abell 3391/95 field: The Northern Clump

Cited by 12 publications

References 68 publications

The eROSITA view of the Abell 3391/95 field: Case study from the Magneticum cosmological simulation

The eROSITA view of the Abell 3391/95 field: Case study from the Magneticum cosmological simulation

eROSITA spectro-imaging analysis of the Abell 3408 galaxy cluster

The eROSITA Final Equatorial-Depth Survey (eFEDS)

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