A study of the large-scale formation in the environment of A3266: Infalling groups, filaments, and a premerger cold front

Abstract

Abell 3266 (A3266) is a dynamically active galaxy cluster embedded in a dense environment of galaxy groups and clusters at similar redshift. Data from the Spektrum Roentgen Gamma (SRG)/eROSITA all-sky survey enable the study of faint X-ray emission in cluster outskirts. We investigate the previously unexplored outskirts of A3266 out to $3R_{100}$, characterize its nearest neighboring galaxy group, and search for connecting filaments using X-ray emission and galaxy number density. We performed X-ray imaging, surface brightness, and spectral analyses in selected regions and sectors. These were complemented by the distribution of member galaxies from the NASA/IPAC Extragalactic Database NED and by comparison with the cosmological simulation Simulating the LOcal Web (SLOW). We detect an X-ray filament connecting A3266 to its nearest northwestern group over a 3D length of $L_{R_{200}\text{–}{R}_{200}}={1.1}_{-0.1}^{+0.5},\mathrm{Mpc}$ with a significance of $3.6,\ddot{I}ƒ$. The group exhibits cool-core properties and is embedded within the filament. The filament has a temperature of $T={1.2}_{-0.2}^{+0.3},\mathrm{keV}$, metallicity $Z={0.07}_{-0.05}^{+0.09},Z\odot$, and, assuming a simple geometry, an electron number density of $n_{\mathrm{e}}=8_{-2}^{+1}\times 10^{-5},{\mathrm{cm}}^{-3}$. Our findings reveal a coherent network of galaxy groups around A3266, tracing its ongoing assembly along the large-scale structure. The filament is hotter and denser than expected for pristine warm-hot intergalactic medium, consistent with gas processed in the cluster environment and influenced by the infall of the northwestern group. Comparison with SLOW shows that the observed group distribution and filamentary connections are qualitatively consistent with an actively accreting cluster embedded in the cosmic web.

10 pages and 13 figures in the main text plus 2 pages and 2 figures as appendix. Astronomy & Astrophysics, accepted on June 29, 2026

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