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Yasushi Suto

Publications and source records attributed to Yasushi Suto.

171 records · Page 10Linked to original sources
arXiv1996

Cosmological Redshift-Space Distortion II: distance in an inhomogeneous universe and evolution of bias

We discuss the two potentially important effects which should be taken into account in the analysis of the cosmological redshift-space distortion especially at high redshifts; the effect of inhomogeneities in the light propagation and the evolution of bias. Although such inhomogeneities affect significantly the degree of the cosmological redshift distortion, one can determine the density parameter $Ω_0$ from the distortion pattern at $z=0$, and the cosmological constant $λ_0$ from that at $z = (1\sim 2)$. In particular we show that in low-density ($Ω_0\ll 1$) universes one can determine the value of $λ_0$ and even the evolution of the bias parameter almost insensitively to the degree of the clumpiness of the matter distribution in the universe.

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arXiv1996

Cosmological Redshift Distortion of Correlation Functions as a Probe of the Density Parameter and the Cosmological Constant

We propose cosmological redshift-space distortion of correlation functions of galaxies and quasars as a probe of both the density parameter $Ω_0$ and the cosmological constant $λ_0$. In particular, we show that redshift-space distortion of quasar correlation functions at $z\sim2$ can in principle set a constraint on the value of $λ_0$. This is in contrast to the popular analysis of galaxy correlation functions in redshift space which basically determines $Ω_0^{0.6}/b$, where $b$ is the bias parameter, but is insensitive to $λ_0$. For specific applications, we present redshift-space distortion of correlation functions both in cold dark matter models and in power-law correlation function models, and discuss the extent to which one can discriminate between the different $λ_0$ models.

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arXiv1996

Semi-analytic predictions for statistical properties of X-ray clusters of galaxies in cold dark matter universes

Temperature and luminosity functions of X-ray clusters are computed semi-analytically, combining a simple model for the cluster gas properties with the distribution functions of halo formation epochs proposed by Lacey & Cole (1993) and Kitayama & Suto (1996). In contrast to several previous approaches which apply the Press--Schechter mass function in a straightforward manner, our method can explicitly take into account the temperature and luminosity evolution of clusters. In order to make quantitative predictions in a specific cosmological context, we adopt cold dark matter (CDM) universes. Assuming the baryon density parameter $Ω_{\rm B}=0.0125 h^{-2}$ ($h$ is the Hubble constant in units of 100 km$\cdot$sec$^{-1}\cdot$Mpc$^{-1}$) and the {\it COBE} normalization of matter fluctuations, temperature and luminosity functions of X-ray clusters depend sensitively on the density parameter $Ω_0$. Allowing for several uncertainties in observational data as well as in our simplified assumptions, we conclude that $Ω_0 \sim 0.2-0.5$ and $h\sim 0.7$ CDM models with/without the cosmological constant reproduce simultaneously the observed temperature and luminosity functions of X-ray clusters at redshift $z\sim0$.

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arXiv1996

The X-ray halo of the Local Group and the CMB quadrupole

Since recent X-ray observations have revealed that most clusters of galaxies are surrounded by an X-ray emitting gaseous halo, it is reasonable to expect that the Local Group of galaxies has its own X-ray halo. We show that such a halo, with temperature $\sim 1\keV$ and column density $\sim O(10^{21}) {\rm cm}^{-2}$, is a possible source for the excess low-energy component in the X-ray background. The halo should also generate temperature anisotropies in the microwave background via the Sunyaev-Zel'dovich effect. Assuming an isothermal spherical halo with the above temperature and density, the amplitude of the induced quadrupole turns out to be comparable to the COBE data without violating the upper limit on the $y$-parameter.

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arXiv1996

Formation rate of gravitational structures and the cosmic X-ray background radiation

Analytical expressions for the rates of formation and destruction of gravitationally bound systems are derived assuming that they are originated from primordial random-Gaussian density fluctuations. The resulting formulae reproduce the time derivative of the Press-Schechter mass function in a certain limit. Combining a theoretical model for the evolution of structures with the formation rate, we can make various cosmological predictions which are to be compared with observations. As an example to elucidate such applicability, we evaluate the contribution of clusters of galaxies to the cosmic X-ray background radiation. With the {\it COBE} normalization, we find that the significant fraction of the observed soft X-ray background is accounted for by clusters of galaxies in a cold dark matter universe with $Ω_0 \sim 0.2$, $λ_0 =1- Ω_0$ and $h \sim 0.8$.

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arXiv1996

The X-ray halo of the Local Group and its implications for microwave and soft X-ray background

Since recent X-ray observations have revealed that most clusters of galaxies are surrounded by an X-ray emitting gaseous halo, it is reasonable to expect that the Local Group of galaxies has its own X-ray halo. We show that such a halo, with temperature $\sim 1$keV and column density $\sim O(10^{21}) {\rm cm}^{-2}$, is a possible source for the excess low-energy component in the X-ray background. The halo should also generate temperature anisotropies in the microwave background via the Sunyaev-Zel'dovich effect. Assuming an isothermal spherical halo with the above temperature and density, the amplitude of the induced quadrupole turns out to be comparable to the COBE data without violating the upper limit on the $y$-parameter. The induced dipole is negligible compared to the peculiar velocity of the Local Group, and multipoles higher than quadrupole are generally much smaller than the observed ones. However non-sphericity and/or clumpiness of the halo will produce a stronger effect. Therefore the gaseous halo of the Local Group, if it exists, will affect the estimate of the primordial spectral index $n$ and the amplitude of the density fluctuations deduced from the {\sl COBE} data.

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arXiv1995

Nonlinear Evolution of Genus in Primordial Random-Gaussian Density Field

The genus statistics is studied using large $N$-body simulations for several cosmological models. We consider the effects of nonlinear gravitational evolution, smoothing the particle data in fully nonlinear regime, and the redshift-space distortion on the genus curve. Detailed comparison between the theoretical prediction in weakly nonlinear theory and the appropriate simulation results shows that the analytic formula describes the behavior of genus in weakly nonlinear regime fairly accurately. We also find that the redshift-space distortion on genus statistics is small in linear and weakly nonlinear regimes. We conclude that if weakly nonlinear theory and direct numerical simulations are combined, the normalized genus curve $G(ν)/G(0)$ is a powerful tool to directly check the random-Gaussian paradigm of the origin of the large-scale structure in the universe.

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arXiv1994

Angular two-point correlation functions for cosmological gamma-ray burst model

We compute the angular two-point correlation functions of the gamma-ray bursts at cosmological distances. Since the gamma-ray burst emission mechanism is not yet established, we simply assume that the gamma-ray burst sources are associated with high-redshift galaxies in some way. Then on the basis of several simple models for the evolution of galaxy spatial correlations, we calculate the amplitude of angular two-point correlation functions on scales appropriate for the Compton Gamma Ray Observatory data. we find that in most cases the predicted correlations are difficult to detect with the current data rate and the angular resolution, but models in which the bursts preferentially occur at relatively low redshift ($z \simlt 0.5$) predict correlation amplitudes on $θ\sim 5^\circ$ which will be marginally detectable with the Gamma Ray Observatory data in several years. If future observations detect a signal of angular correlations, it will imply useful information on the correlation of galaxies at high redshifts provided that the gamma-ray bursts are cosmological.

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arXiv1993

Microwave Background Anisotropies in Primeval Isocurvature Baryon Models: Constraints on the Cosmological Parameters

We have performed the most comprehensive predictions of the temperature fluctuations \dtt in the primeval isocurvature baryon models to see whether or not the models are consistent with the recent data on the cosmic microwave background anisotropies. More specifically, we computed the \dtt corresponding to the experimental set-up by the South-Pole and the Owens Valley experiments as well as the COBE satellite. The amplitudes of the predicted \dtt are normalized by means of the COBE 10$^\circ$ data. The resulting constraints on the models are presented on $n - Ω_b$ plane in the case of $λ_0=1-Ω_b$ (flat models) and $λ_0=0$ (open models), where $n$ is the primordial spectral index of entropy fluctuations and $Ω_b$ is the present baryon density parameter. Our results imply that the PIB models cannot be reconciled with the current observations for any reasonable set of cosmological parameters.

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