Hierarchical Structure of Astronomical Objects in the Cosmic String Scheme

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The hierarchical structure of astronomical objects is investigated in the cosmic string scheme with cold dark matter (CDM). A non-linear dark matter potential is formed in the crossing site of three wakes triggered at around z_i by moving strings. If we use this scheme, the mass and radius of formed CDM objects increase gradually as M ∝ (1+z)^<-3> and R ∝ (1+z)^<-2>, and objects triggered at z_i ≃ 10^4, 10^5 and 10^6 grow to become objects corresponding to clusters of galaxies, galaxies and dwarf galaxies, respectively. The number densities of these objects n(z_i) are related to the size l(z_i,z) as n(z_i) ∝ 1/l(z_i,z)^3, where l(z_i,z) is the horizon size of the stage z_i observed at z. One of the interesting points of this scheme is that smaller objects are gradually accreted into larger ones. For example, dwarf galaxies have been nostly accreted into galaxies at the present. Galaxies are still now accumulating toward clusters of galaxies, and consequently many of accreted galaxies are found as E or SO type galaxies there. In the future, or possibly even at the present time, clusters of galaxies will be accreted into superclusters of galaxies triggered at z_i ≃ 10^3. Heating through the accumulation of baryonic matter in the CDM gravitational potential is also investigated and it is found that their heating is not sufficient to reionize the universe before z ≃ 5. Therefore some other heating sources or mechanisms are required. However, heating through the accumulation of baryonic matter could explain the X-ray properties of clusters of galaxies.
理論物理学刊行会の論文
1999-07-25

Hierarchical Structure of Astronomical Objects in the Cosmic String Scheme

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