Masahiro Morikawa

Publications (3)10.92 Total impact

• Article: Why is the Zel'dovich Approximation So Accurate?

  Ayako Yoshisato, Masahiro Morikawa, Naoteru Gouda, and Hideaki Mouri
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  ABSTRACT: Why does the Zel'dovich approximation (ZA) work well to describe gravitational collapse in the universe? This problem is examined by focusing on its dependence on the dimensionality of the collapse. The ZA is known to be exact for a one-dimensional collapse. We show that the ZA becomes progressively more accurate in the order of three-, two-, and one-dimensional collapses. Furthermore, using models for spheroidal collapse, we show that the ZA remains accurate in all collapses, which become progressively lower dimensional with the passage of time. That is, the ZA is accurate because the essence of the gravitational collapse is incorporated in the ZA.
  The Astrophysical Journal 12/2008; 637(2):555. · 6.02 Impact Factor
• Article: Negative skewness of radial pairwise velocity in the quasi‐non‐linear regime: Zel'dovich approximation

  Ayako Yoshisato, Masahiro Morikawa, Hideaki Mouri
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  ABSTRACT: According to N-body numerical simulations, the radial pairwise velocities of galaxies have negative skewness in the quasi-non-linear regime. To understand its origin, we calculate the probability distribution function of the radial pairwise velocity using the Zel'dovich approximation, i.e. an analytical approximation for gravitational clustering. The calculated probability distribution function is in good agreement with the result of N-body simulations. Thus, the negative skewness originates in relative motions of galaxies in the clustering process that the infall dominates over the expansion.
  Monthly Notices of the Royal Astronomical Society 07/2003; 343(3):1038 - 1044. · 4.90 Impact Factor
• Source

  Available from: ArXiv

  Article: Accuracy of Nonlinear Approximations in Spheroidal Collapse --- Why are Zel'dovich-type approximations so good? ---

  Ayako Yoshisato, Takahiko Matsubara, Masahiro Morikawa
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  ABSTRACT: Among various analytic approximations for the growth of density fluctuations in the expanding Universe, Zel'dovich approximation and its extensions in Lagrangian scheme are known to be accurate even in mildly non-linear regime. The aim of this paper is to investigate the reason why these Zel'dovich-type approximations work accurately beyond the linear regime from the following two points of view: (1) Dimensionality of the system and (2) the Lagrangian scheme on which the Zel'dovich approximation is grounded. In order to examine the dimensionality, we introduce a model with spheroidal mass distribution. In order to examine the Lagrangian scheme, we introduce the Pad\'e approximation in Eulerian scheme. We clarify which of these aspects supports the unusual accuracy of the Zel'dovich-type approximations. We also give an implication for more accurate approximation method beyond the Zel'dovich-type approximations. Comment: 25 pages, latex, 7 figures included
  07/1997;