Are fossil groups early-forming galaxy systems?

Abstract

Using the Illustris cosmological simulation, we investigate the origin of fossil groups in the $M_{200}=10^{13}-10^{13.5}{M}_{\odot }/h$ mass regime. We examine the formation of the two primary features of fossil groups: the large magnitude gap between their two brightest galaxies, and their exceptionally luminous brightest group galaxy (BGG). For fossils and non-fossils identified at $z=0$, we find no difference in their halo mass assembly at early times, departing from previous studies. However, we do find a significant difference in the recent accretion history of fossil and non-fossil halos; in particular, fossil groups show a lack of recent accretion and have in majority assembled 80\% of their $M_{200}(z=0)$ mass before $z\sim 0.4$. For fossils, massive satellite galaxies accreted during this period have enough time to merge with the BGG by the present day, producing a more massive central galaxy; and, the lack of recent group accretion prevents replenishment of the bright satellite population, allowing for a large magnitude gap to develop within the past few Gyr. We thus find that the origin of the magnitude gap and overmassive BGG of fossils in Illustris depends on the recent accretion history of the groups and merger history of the BGG after their collapse at $z\sim 1$. This indicates that selecting galaxy groups by their magnitude gap does not guarantee obtaining neither early-forming galaxy systems nor undisturbed central galaxies.

arXiv comment12 pages, 10 figures, 3 tables. Accepted for publication in ApJ

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Cited by in corpus (18)

• The Impact of Environment on the Stellar Mass - Halo Mass Relation
• Supercluster A2142 and collapse in action - infalling and merging groups and galaxy transformations
• Aging Halos: Implications of the Magnitude Gap on Conditional Statistics of Stellar and Gas Properties of Massive Halos
• What sets the splashback radius of dark matter haloes: accretion history or other properties?
• On Mass Concentrations & Magnitude Gaps of Galaxy Systems in the CS82 Survey
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• Fossil group origins: VIII RXJ075243.6+455653 a transitionary fossil group
• Cosmic Pathways for Compact Groups in the Milli-Millennium Simulation
• Is Abell 2261 a fossil galaxy cluster in a transitional dynamical state?
• A Rich Satellite Population of the NGC 4437 Group and Implications of a Magnitude Gap for Galaxy Group Assembly History
• Assembly Conformity of Structure Growth: Fossil versus Normal Groups of Galaxies
• Powerful yet lonely: Is 3C 297 a high-redshift fossil group?