Discovery of a >13 Mpc long X-ray filament between two galaxy clusters beyond three times their virial radii

Abstract

The new Spectrum Roentgen Gamma (SRG) eROSITA X-ray telescope has a superior response to extended soft X-rays, which makes it ideal for studying low X-ray surface brightness emission of cosmic filaments. We search for extended X-ray emission between the two nearby galaxy clusters Abell~3667 and Abell~3651, which are separated by a projected transverse distance of $\sim 13\mathrm{Mpc}$, using data from the SRG/eROSITA All-Sky Survey. We performed a detailed X-ray image analysis of the region between the two galaxy clusters and conducted a redshift analysis of the sources between them. We carried out a thorough surface brightness and spectral analysis between the clusters. The analysis was complemented with an X-ray pointed observation from XMM-Newton, infrared 2MASS data, and redshift information from NED. We discover an emission filament beyond the known radio relic northwest of A3667 and even beyond three times its virial radius. It is smoothly connected to A3651. The X-ray emission in the direction of the filament shows an enhancement of $30\pm 3\%$ with a significance of $11\sigma$. The 2MASS map and redshift analysis show an alignment of galaxies along the filament and make a projection effect unlikely. Taking the redshift progression of galaxies within the filament into account, we estimate its three-dimensional length to be in the range of $25\mathrm{Mpc}-32\mathrm{Mpc}$. The surface brightness analysis in combination with the temperature $T=({0.91}_{-0.11}^{+0.07})\mathrm{keV}$ and metallicity $Z=({0.10}_{-0.08}^{+0.05}){\mathrm{Z}}_{\odot }$ from the spectral analysis leads to estimates of a total flux, gas mass, and central baryon overdensity of $F_{\mathrm{X}}=(7.4\pm 1.2)\times 10^{-12}\mathrm{erg}{\mathrm{s}}^{-1}\mathrm{c}{\mathrm{m}}^{-2}$, $M_{\mathrm{g}}=(2.7_{-0.8}^{+1.4})\times 10^{14}{\mathrm{M}}_{\odot }$ and ${\delta }_0=215_{-50}^{+86}$.

12 pages and 13 figures in the main text plus 3 pages and 3 figures as appendix. Astronomy & Astrophysics, accepted on September 25, 2024. Now with included spectral analysis

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• CHANCES, the Chilean Cluster Galaxy Evolution Survey: Selection and initial characterisation of clusters and superclusters
• The impact of assembly history on the X-ray detectability of halos. From galaxy groups to galaxy clusters
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• The SRG/eROSITA all-sky survey: View of the Fornax galaxy cluster
• Detection of pure warm-hot intergalactic medium emission from a $7.2$ Mpc long filament in the Shapley supercluster using X-ray spectroscopy
• Turbulence in Simulated Local Cluster Analogs: One-to-one comparisons between SLOW and XRISM/Hitomi
• The thermodynamic structure and large-scale structure filament in MACS J0717.5+3745
• Cosmological simulation of a radio synchrotron bridge between pre-merging galaxy clusters
• X-ray emission in IllustrisTNG circum-cluster environments. II -- Possible origins of the soft X-ray excess emission