2005ApJ...630L.109D -
Astrophys. J., 630, L109-L112 (2005/September-2)
The formation of fossil galaxy groups in the hierarchical universe.
D'ONGHIA E., SOMMER-LARSEN J., ROMEO A.D., BURKERT A., PEDERSEN K., PORTINARI L. and RASMUSSEN J.
Abstract (from CDS):
We use a set of 12 high-resolution N-body/hydrodynamical simulations in the ΛCDM cosmology to investigate the origin and formation rate of fossil groups (FGs), which are X-ray-bright galaxy groups dominated by a large elliptical galaxy, with the second brightest galaxy being at least 2 mag fainter. The simulations invoke star formation, chemical evolution with noninstantaneous recycling, metal-dependent radiative cooling, strong starburst-driven galactic superwinds, effects of a metagalactic UV field, and full stellar population synthesis. We find an interesting correlation between the magnitude gap between the brightest and second-brightest galaxy and the formation time of the group. It is found that FGs have already assembled half of their final dark matter mass at z≳1, and subsequently they typically grow by minor merging only, whereas non-FGs on average form later. The early assembly of FGs leaves sufficient time for galaxies of L∼L*to merge into the central one by dynamical friction, resulting in the large magnitude gap at z=0. About 33%±16% of the groups simulated are found to be FGs, whereas the observational estimate is ∼10%-20%. The FGs are found to be overluminous in the X-ray relative to non-FGs of the same optical luminosity, in qualitative agreement with observations. Finally, from a dynamical friction analysis, we find that FGs exist at all only because infall of L∼L*galaxies happens along filaments with small impact parameters.
Abstract Copyright:
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Journal keyword(s):
Cosmology: Observations - Cosmology: Dark Matter - Galaxies: Clusters: General - Galaxies: Formation
Simbad objects:
3
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