Vol 16, No 3

Chandra Studies of the X-ray gas properties of fossil systems

Zhen-Zhen Qin


Abstract We study ten galaxy groups and clusters suggested in the literature to be “fossil systems (Fss)” based on Chandra observations. According to the M500 − T and LX − T relations, the gas properties of Fss are not physically distinct from ordinary galaxy groups or clusters. We also first study the fgas,2500 − T relation and find that the FSs exhibit the same trend as ordinary systems. The gas densities of FSs within 0.1r200 are ∼ 10−3 cm−3 , which is the same order of magnitude as galaxy clusters. The entropies within 0.1r200 (S 0.1r200) of FSs are systematically lower than those in ordinary galaxy groups, which is consistent with previous reports, but we find their S 0.1r200 − T relation is more similar to galaxy clusters. The derived mass profiles of FSs are consistent with the Navarro, Frenk and White model in (0.1 − 1)r200 , and the relation between scale radius rs and characteristic mass density δc indicates self-similarity of dark matter halos of FSs. The ranges of rs and δc for FSs are also close to those of galaxy clusters. Therefore, FSs share more common characteristics with galaxy clusters. The special birth place of the FS makes it a distinct type of galaxy system.


Keywords galaxies: cluster: general — galaxies: evolution — galaxies: halos — intergalactic medium — X-ray: galaxies: clusters

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