Fossil group origins XII. Large-scale environment around fossil systems

Abstract

We analyse the large-scale structure out to 100 Mpc around a sample of 16 confirmed fossil systems using spectroscopic information from the Sloan Digital Sky Survey Data Release 16. We compute the distance between our FGs and the centres of filaments and nodes presented in \citet{Chen2016}. We also study the density of bright galaxies, since they are thought to be good mass tracers, and the projected over densities of galaxies. Finally, we apply a FoF algorithm to detect virialised structures around our FGs, in order to have an estimate of the mass available in their surroundings. FGs are mainly found close to filaments, with a mean distance of $3.7\pm 1.1$ R${}_{200}$ and a minimum distance of 0.05 $R_{200}$. On the other hand, none of our FGs is found close to intersections, with a mean and minimum distance of $19.3\pm 3.6$ and 6.1 $R_{200}$, respectively. There is a correlation for which FGs at higher redshifts are found in denser regions, when we use bright galaxies as tracers of the mass. At the same time, FGs with the largest magnitude gaps ($\Delta m_{12}$ > 2.5) are found in less dense environments and hosting, on average, smaller central galaxies. Our results suggest that FGs formed in a peculiar position of the cosmic web, close to filaments and far from nodes, in which their interaction with the cosmic web itself can be limited. We deduce that FGs with faint BCGs, large $\Delta m_{12}$, and low redshifts could be systems at the very last stage of their evolution. Moreover, we confirm theoretical predictions that systems with the largest magnitude gap are not massive.

23 pages, 10 figures, and 2 tables. Accepted for publication on Astronomy and Astrophysics

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• Fossil group origins XIII. A paradigm shift: fossil groups as isolated structures rather than relics of the ancient Universe
• Where do X-ray low surface brightness clusters sit with respect to filaments?
• Galaxy groups in various evolutionary stages