Fossil Group Origins VII. Galaxy substructures in fossil systems

Abstract

Fossil groups are expected to be the final product of galaxy merging within galaxy groups. In simulations, they are predicted to assemble their mass at high redshift. This early formation allows for the innermost $M^{\ast }$ galaxies to merge into a massive central galaxy. Then, they are expected to maintain their fossil status because of the few interactions with the large-scale structure. In this context, the magnitude gap between the two brightest galaxies of the system is considered a good indicator of its dynamical status. As a consequence, the systems with the largest gaps should be dynamically relaxed. In order to examine the dynamical status of these systems, we systematically analyze, for the first time, the presence of galaxy substructures in a sample of 12 spectroscopically-confirmed fossil systems with redshift $z\le 0.25$. We apply a number of tests in order to investigate the substructure in fossil systems in the two-dimensional space of projected positions out to $R_{200}$. Moreover, for a subsample of 5 systems with at least 30 spectroscopically-confirmed members we also analyze the substructure in the velocity and in the three-dimensional velocity-position spaces. Additionally, we look for signs of recent mergers in the regions around the central galaxies. We find that an important fraction of fossil systems show substructure. The fraction depends critically on the adopted test, since each test is more sensible to a particular type of substructure. Our interpretation of the results is that fossil systems are not, in general, as relaxed as expected from simulations. Our sample of 12 spectroscopically-confirmed fossil systems need to be extended in order to compute an accurate fraction, but our conclusion is that it is similar to the fraction of substructure detected in non-fossil clusters. THIS ABSTRACT IS TRUNCATED.

12 pages, 5 figures, accepted for publication in A&A

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Cited by in corpus (16)

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• The hot gas content of fossil galaxy clusters
• On Mass Concentrations & Magnitude Gaps of Galaxy Systems in the CS82 Survey
• Fossil group origins IX. Probing the formation of fossil galaxy groups with stellar population gradients of their central galaxies
• Fossil group origins. XI. The dependence of galaxy orbits on the magnitude gap
• Fossil group origins XII. Large-scale environment around fossil systems
• Fossil group origins XIII. A paradigm shift: fossil groups as isolated structures rather than relics of the ancient Universe
• Assembly bias evidence in close galaxy pairs
• Fossil group origins: VIII RXJ075243.6+455653 a transitionary fossil group
• Candidate fossil groups in the CFHTLS: a probabilistic approach
• Is Abell 2261 a fossil galaxy cluster in a transitional dynamical state?
• Assembly Conformity of Structure Growth: Fossil versus Normal Groups of Galaxies
• Somewhere in between: Tracing the Radio Emission from Galaxy Groups (or Why Does the Future of Observing Galaxy Groups with Radio Telescopes Look Promising?)
• The Way to Quench: Galaxy evolution in Abell 2142
• Cosmo-Paleontology: Statistics of Fossil Groups in a Gravity-Only Simulation