Statistical Analysis of Galaxies and Clusters in Spatially Flat Cold Dark Matter Universe

空間的に平坦な冷たいダークマター宇宙のもとでの銀河及び銀河団の定量的解析

上田 晴彦

Spatial distributions and dynamical properties of galaxies and clusters of galaxies are studied in various cosmological models, in order to investigate the dependence of these properties of galaxies and clusters on the density parameter Ω0 and the dimensionless cosmological parameter λ0. In accordance with the inflation hypothesis, we confirm ourselves to the spatially flat models with Ω0 + λ0 = 1. For the dark matter we assume the Cold Dark Matter (CDM) cosmological model which is believed to be most reliable at present. We keep our eye upon this dark matter and estimate these properties numerically.

In order to treat the distribution of galaxies and clusters of galaxies statistically, we first examine the effectiveness of various statistical measure for quantifying the spatial distribution of galaxies. Counts-in-cells and multi-fractal analysis are examined in detail, and are compared with the correlation statistics. A measure similar to the percolation test in count-in-cells analysis provides a useful guide for quantifying the pattern, at least in a complementary manner to the correlation function. We found, however, that it also sensitively depends on the geometry of samples of galaxies. Multi-fractal measures are defined only in a somewhat ambiguous manner due to the discrete nature of galaxy distribution. Then we conclude that although all of them have been successful to some extent in quantitatively describing the pattern of galaxy clustering, none seems to be particularly superior to the two-point correlation function in distinguishing the underlying structure.

Next we examine the distribution of galaxies and clusters obtained to N-body simulation in CDM model in comparison with their observational results. Specifically we consider two spatially flat CDM models: the Ω0 = 1.0 CDM and Ω0 = 0.2 CDM model. Galaxies or clusters in these simulations are identified by means of refined friends-of-friends algorithm. We pay attention to the spatial and velocity correlation functions of galaxies and clusters. The overall conclusion is that the Ω0 = 1.0 CDM model generally fails to reproduce the observed properties of the two-point correlation functions of the clusters, as has been claimed recently in various independent analyses, while the Ω0 = 0.2 CDM model is quite successful. In addition to this correlation analysis, we have studied dynamical properties of halos and clusters, by using velocity functions and angular momentum distribution. We found that the Ω0 = 1.0 CDM simulations reproduce the velocity functions in reasonable agreement with the Press-Schechter theory, but the Ω0 = 0.2 CDM simulations do not. Quantitative comparison of our velocity functions with the available observational data revealed that only the standard CDM model with a high biasing parameter b ~ 2 is consistent with the observation. The distribution of the dimensionless angular momentum λ is very broad (0.01 ≲ λ ≲ 0.1) and the functional form of the distribution looks very universal and is quite insensitive both to the cosmological parameters and to the fluctuation spectral shape. Although the spatial distribution of the angular momentum does not show any noticeable correlation of the orientation, halos with relatively small λ preferentially cluster around dense regions.

From our analysis, it is found that almost all CDM models with the Harrison-Zel'dovich primordial spectrum seem to be ruled out, although the Ω0 = 0.2 CDM universe is more preferable than the Ω0 = 1.0 CDM universe. Only the gravitational effect has been so far considered in our analysis, and we have not taken account of other elements, such as the effect of fluidal gas within galaxies and clusters. More statistically reliable observational results and more useful SPH (smoothed particle mesh) simulation models are needed for their detail analyze.

天文学・宇宙科学 [ 440 ]

英語

Copyright(c) by Author

Ueda, H., Itoh, M., & Suto, Y. Publ. Astron. Soc. Japan. Vol.45 7 (1993) ～を参照している

Ueda, H., Itoh, M., & Suto, Y. Astrophys. Jarnal. Vol.408 3 (1993) ～を参照している

Ueda, H., Shimasaku, K., Suginohara, T., & Suto, Y. YITP-preprint ～を参照している

[URI] http://adsabs.harvard.edu/abs/1993PASJ...45....7U ～を参照している

[DOI] http://dx.doi.org/10.1086/172564 ～を参照している

[URI] http://adsabs.harvard.edu/abs/1994PASJ...46..319U ～を参照している

[URI] http://adsabs.harvard.edu/abs/1995PASJ...47..389U ～を参照している

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