Volume 647, March 2021
First science highlights from SRG/eROSITA
|Number of page(s)||30|
|Section||Cosmology (including clusters of galaxies)|
|Published online||26 February 2021|
The Abell 3391/95 galaxy cluster system
A 15 Mpc intergalactic medium emission filament, a warm gas bridge, infalling matter clumps, and (re-) accelerated plasma discovered by combining SRG/eROSITA data with ASKAP/EMU and DECam data★
Argelander-Institut für Astronomie (AIfA), Universität Bonn, Auf dem Hügel 71, 53121
2 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany
3 Ludwig-Maximilians-Universität München, Scheinerstraße 1, München, Germany
4 Universität Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
5 National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
6 Astronomy Department, University of Geneva Ch. d’Ecogia 16, 1290 Versoix, Switzerland
7 University of La Serena, La Serena, Chile
8 Cerro Tololo Inter-American Observatory, NSF’s National Optical-Infrared Astronomy Research Laboratory, Casilla 603, La Serena, Chile
9 School of Physics & Astronomy, Monash University, Clayton, VIC 3800, Australia
10 CSIRO Astronomy & Space Science, PO Box 76, Epping, NSW 1710, Australia
11 Instituto de Física de Cantabria (CSIC-UC), Avda. Los Castros s/n, 39005 Santander, Spain
12 Australian Astronomical Optics, Macquarie University, 105 Delhi Rd, North Ryde, NSW 2113, Australia
13 School ofScience, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
14 ESO – European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
15 Minnesota Institute forAstrophysics, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455, USA
16 The Inter-University Institute for Data Intensive Astronomy (IDIA), Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
17 Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
18 Department of Physics, Nara Women’s University, Kitauoyanishi-machi, Nara 630-8506, Japan
19 Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) Projektträger, Joseph-Beuys-Allee 4, 53113 Bonn, Germany
Accepted: 3 November 2020
Context. Inferences about dark matter, dark energy, and the missing baryons all depend on the accuracy of our model of large-scale structure evolution. In particular, with cosmological simulations in our model of the Universe, we trace the growth of structure, and visualize the build-up of bigger structures from smaller ones and of gaseous filaments connecting galaxy clusters.
Aims. Here we aim to reveal the complexity of the large-scale structure assembly process in great detail and on scales from tens of kiloparsecs up to more than 10 Mpc with new sensitive large-scale observations from the latest generation of instruments. We also aim to compare our findings with expectations from our cosmological model.
Methods. We used dedicated SRG/eROSITA performance verification (PV) X-ray, ASKAP/EMU Early Science radio, and DECam optical observations of a ~15 deg2 region around the nearby interacting galaxy cluster system A3391/95 to study the warm-hot gas in cluster outskirts and filaments, the surrounding large-scale structure and its formation process, the morphological complexity in the inner parts of the clusters, and the (re-)acceleration of plasma. We also used complementary Sunyaev-Zeldovich (SZ) effect data from the Planck survey and custom-made Galactic total (neutral plus molecular) hydrogen column density maps based on the HI4PI and IRAS surveys. We relate the observations to expectations from cosmological hydrodynamic simulations from the Magneticum suite.
Results. We trace the irregular morphology of warm and hot gas of the main clusters from their centers out to well beyond their characteristic radii, r200. Between the two main cluster systems, we observe an emission bridge on large scale and with good spatial resolution. This bridge includes a known galaxy group but this can only partially explain the emission. Most gas in the bridge appears hot, but thanks to eROSITA’s unique soft response and large field of view, we discover some tantalizing hints for warm, truly primordial filamentary gas connecting the clusters. Several matter clumps physically surrounding the system are detected. For the “Northern Clump,” we provide evidence that it is falling towards A3391 from the X-ray hot gas morphology and radio lobe structure of its central AGN. Moreover, the shapes of these X-ray and radio structures appear to be formed by gas well beyond the virial radius, r100, of A3391, thereby providing an indirect way of probing the gas in this elusive environment. Many of the extended sources in the field detected by eROSITA are also known clusters or new clusters in the background, including a known SZ cluster at redshift z = 1. We find roughly an order of magnitude more cluster candidates than the SPT and ACT surveys together in the same area. We discover an emission filament north of the virial radius of A3391 connecting to the Northern Clump. Furthermore, the absorption-corrected eROSITA surface brightness map shows that this emission filament extends south of A3395 and beyond an extended X-ray-emitting object (the “Little Southern Clump”) towards another galaxy cluster, all at the same redshift. The total projected length of this continuous warm-hot emission filament is 15 Mpc, running almost 4 degrees across the entire eROSITA PV observation field. The Northern and Southern Filament are each detected at >4σ. The Planck SZ map additionally appears to support the presence of both new filaments. Furthermore, the DECam galaxy density map shows galaxy overdensities in the same regions. Overall, the new datasets provide impressive confirmation of the theoretically expected structure formation processes on the individual system level, including the surrounding warm-hot intergalactic medium distribution; the similarities of features found in a similar system in the Magneticum simulation are striking. Our spatially resolved findings show that baryons indeed reside in large-scale warm-hot gas filaments with a clumpy structure.
Key words: galaxies: clusters: individual: Abell 3391 / galaxies: clusters: individual: Abell 3395 / galaxies: clusters: intracluster medium / intergalactic medium / large-scale structure of Universe / X-rays: galaxies: clusters
Movies associated to Figs. 6 and 7 are available at https://www.aanda.org
© ESO 2021
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