Fossil Groups in the Millennium Simulation: Their environment and its evolution

Abstract

Fossil systems are defined to be X-ray bright galaxy groups with a 2-magnitude difference between their two brightest galaxies within half the projected virial radius,and represent an interesting extreme of the population of galaxy agglomerations.However,the physical conditions and processes leading to their formation are still poorly constrained.We compare the outskirts of fossil systems with that of normal groups to understand whether environmental conditions play a significant role in their formation.We study galaxy groups in both,numerical simulations and observations.We use a variety of statistical tools including the spatial cross-correlation function and the local density parameter Δ_5 to probe differences in the density and structure of the environments of normal and fossil systems in the Millennium simulation.We find that the number density of galaxies surrounding fossil systems evolves from greater than that observed around normal systems at z=0.69, to lower than the normal systems by z=0.Both fossil and normal systems exhibit an increment in their otherwise radially declining local density measure (Δ_5) at distances of order 2.5r_{vir} from the system centre.We show that this increment is more noticeable for fossil systems than normal systems and demonstrate that this difference is linked to the earlier formation epoch of fossil groups.Despite the importance of the assembly time, we show that the environment is different for fossil and non-fossil systems with similar masses and formation times along their evolution.We also confirm that the physical characteristics identified in the Millennium simulation can also be detected in SDSS observations.Our results confirm the commonly held belief that fossil systems assembled earlier than normal systems but also show that the surroundings of fossil groups could be responsible for the formation of their large magnitude gap.

10 pages, 7 figures, 1 table. Replaced after language edition

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Cited by in corpus (14)

• Creation of cosmic structure in the complex galaxy cluster merger Abell 2744
• Mining the gap: evolution of the magnitude gap in X-ray galaxy groups from the 3 square degree XMM coverage of CFHTLS
• Fossil groups origins II. Unveiling the formation of the brightest group galaxies through their scaling relations
• Properties of fossil groups in cosmological simulations and galaxy formation models
• Are fossil groups early-forming galaxy systems?
• Fossil Group Origins VII. Galaxy substructures in fossil systems
• Fossil groups in the Millennium simulation. From the brightest to the faintest galaxies during the past 8 Gyr
• Globular cluster systems in fossil groups: NGC6482, NGC1132 and ESO306-017
• Suzaku Observations of the X-ray Brightest Fossil Group ESO 3060170
• Investigating the cores of fossil systems with Chandra
• Gemini Spectroscopy of Ultra-Compact Dwarfs in the Fossil Group NGC 1132
• Fossil group origins: VIII RXJ075243.6+455653 a transitionary fossil group
• Assembly Conformity of Structure Growth: Fossil versus Normal Groups of Galaxies
• Compact groups from semi-analytical models of galaxy formation -- VI: Evolution of the two first-ranked galaxies