Volume 606, October 2017
|Number of page(s)||8|
|Published online||22 September 2017|
Properties of the cosmological filament between two clusters: A possible detection of a large-scale accretion shock by Suzaku
1 SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, 565-0871 Osaka, Japan
3 Graduate School of Science and Engineering, Kagoshima University, 1-21-35, Korimoto, Kagoshima, 890-0065 Kagoshima, Japan
4 Department of Physics, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, 192-0397 Tokyo, Japan
5 Research Center for Measurement in Advanced Science, Faculty of Science, Rikkyo University 3-34-1, Nishi-Ikebukuro, Toshima-ku, 171-8501 Tokyo, Japan
6 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
7 Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8571 Ibaraki, Japan
8 Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjyuku-ku, Tokyo 162-8601, Japan
Received: 25 January 2017
Accepted: 18 April 2017
We report on the results of a Suzaku observation of the plasma in the filament located between the two massive clusters of galaxies, Abell 399 and Abell 401. Abell 399 (z = 0.0724) and Abell 401 (z = 0.0737) are expected to be in the initial phase of a cluster merger. In the region between the two clusters, we find a clear enhancement in the temperature of the filament plasma from 4 keV (expected value of a typical cluster temperature profile) to kT ~ 6.5 keV. Our analysis also shows that filament plasma is present out to a radial distance of 15′ (1.3 Mpc) from a line connecting the two clusters. The temperature profile is characterized by an almost flat radial shape with kT ~ 6–7 keV within 10′ or ~0.8 Mpc. Across r = 8′ from the axis, the temperature of the filament plasma shows a drop from 6.3 keV to 5.1 keV, indicating the presence of a shock front. The Mach number based on the temperature drop is estimated to be ℳ ~ 1.3. We also successfully determined the abundance profile up to 15′ (1.3 Mpc), showing an almost constant value (Z = 0.3 solar) at the cluster outskirts. We estimated the Compton y parameter to be ~ 14.5 ± 1.3 × 10-6, which is in agreement with the Planck results (14–17 × 10-6 on the filament). The line-of-sight depth of the filament is l ~ 1.1 Mpc, which indicates that the geometry of filament is likely a pancake shape rather than cylindrical. The total mass of the filamentary structure is ~7.7 × 1013M⊙. We discuss a possible interpretation of the drop of X-ray emission at the rim of the filament, which was pushed out by the merging activity and formed by the accretion flow induced by the gravitational force of the filament.
Key words: X-rays: galaxies: clusters / intergalactic medium / galaxies: abundances / large-scale structure of Universe / galaxies: clusters: intracluster medium
© ESO, 2017
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