arXiv subjects

Naoki Itoh

Publications and source records attributed to Naoki Itoh.

29 records · Page 2Linked to original sources

arXiv2003

Relativistic Corrections to the Sunyaev-Zeldovich Effect for Clusters of Galaxies. V. Numerical Results for High Electron Temperatures

We present an accurate numerical table for the relativistic corrections to the thermal Sunyaev-Zeldovich effect for clusters of galaxies. The numerical results for the relativistic corrections have been obtained by numerical integration of the collision term of the Boltzmann equation. The numerical table is provided for the ranges 0.002 <= theta_e <= 0.100 and 0 <= X <= 20, where theta_e = kT_e/mc^2, X = hbar omega/kT_0, T_e is the electron temperature, omega is the angular frequency of the photon, and T_0 is the temperature of the cosmic microwave background radiation. We also present an accurate analytic fitting formula that reproduces the numerical results with high precision.

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arXiv2002

Enhancement of Resonant Thermonuclear Reaction Rates in Extremely Dense Stellar Plasmas

The enhancement factor of the resonant thermonuclear reaction rates is calculated for the extremely dense stellar plasmas in the liquid phase. In order to calculate the enhancement factor we use the screening potential which is deduced from the numerical experiment of the classical one-component plasma. It is found that the enhancement is tremendous for white dwarf densities if the ^{12}C + ^{12}C fusion cross sections show resonant behavior in the astrophysical energy range. We summarize our numerical results by accurate analytic fitting formulae.

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arXiv2002

The r-process in the neutrino winds of core-collapse supernovae and U-Th cosmochronology

The discovery of the second highly $r$-process-enhanced, extremely metal-poor star, CS 31082-001 ([Fe/H] $= -2.9$) has provided a powerful new tool for age determination, by virtue of the detection and measurement of the radioactive species uranium and thorium. One of the serious limitations of this approach, however, is that predictions of the production ratio of U and Th have not been made in the context of a realistic astrophysical model of the $r$-process. We have endeavored to produce such a model, based on the ``neutrino winds'' that are expected to arise from the nascent neutron star of a core-collapse supernova. The mass-integrated $r$-process yields, obtained by assuming a simple time evolution of the neutrino luminosity, are compared to the available spectroscopic elemental abundance data of CS 31082-001. As a result, the ``age'' of this star is determined to be $14.1 \pm 2.5$ Gyr, in excellent agreement with lower limits on the age of the universe estimated by other dating techniques, as well as with other stellar radioactive age estimates. Future measurements of Pt and Pb in this star, as well as expansion of searches for additional $r$-process-enhanced, metal-poor stars (especially those in which both U and Th are measurable), are of special importance to constrain the current astrophysical models for the $r$-process.

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arXiv2001

Relativistic corrections to the multiple scattering effect on the Sunyaev-Zel'dovich effect in the isotropic approximation

We extend the formalism for the calculation of the relativistic corrections to the Sunyaev-Zel'dovich effect for clusters of galaxies and include the multiple scattering effects in the isotropic approximation. We present the results of the calculations by the Fokker-Planck expansion method as well as by the direct numerical integration of the collision term of the Boltzmann equation. The multiple scattering contribution is found to be very small compared with the single scattering contribution. For high-temperature galaxy clusters of kT=15keV, the ratio of the both contributions is -0.2% in the Wien region. In the Rayleigh--Jeans region the ratio is -0.03%. Therefore the multiple scattering contribution is safely neglected for the observed galaxy clusters.

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arXiv2000

Relativistic Corrections to the Sunyaev-Zel'dovich Effect for Clusters of Galaxies. V. Precision Analytic Fitting Formula for the Crossover Frequency Region

We have succeeded in obtaining a precision analytic fitting formula for the exact numerical results of the relativistic corrections to the thermal Sunyaev-Zeldovich effect for clusters of galaxies which has a 1% accuracy for the crossover frequency region where the thermal thermal Sunyaev-Zeldovich effect signal changes from negative to positive sign. The fitting has been carried out for the ranges 0.020 < theta < 0.035 and 0 < X < 15, where theta= kTe/mc^{2}, X = omega/kT0, Te is the electron temperature, omega is the angular frequency of the photon, and T0 is the temperature of the cosmic microwave background radiation. The overall accuracy of the fitting is better than 0.1%. The present analytic fitting formula will be useful for accurate analyses of the thermal Sunyaev-Zeldovich effect for clusters of galaxies.

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arXiv2000

Relativistic Corrections to the Sunyaev-Zel'dovich Effect for Clusters of Galaxies. V. Multiple Scattering

We extend the formalism for the calculation of the relativistic corrections to the Sunyaev-Zel'dovich effect for clusters of galaxies and include the multiple scattering effects. We present a systematic method for the inclusion of the multiple scattering effects. The multiple scattering contribution is found to be very small compared with the single scattering contribution. For high-temperature galaxy clusters of k_{B}T_{e} = 15keV, the ratio of the both contributions is -0.3% in the Wien region. In the Rayleigh--Jeans region the ratio is -0.03%. Therefore the multiple scattering contribution is safely neglected for the observed galaxy clusters.

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arXiv2000

Relativistic Corrections to the Sunyaev-Zel'dovich Effect for Clusters of Galaxies. IV. Analytic fitting formula for the Numerical Results

We present an accurate analytic fitting formula for the numerical results for the relativistic corrections to the thermal Sunyaev-Zel'dovich effect for clusters of galaxies. The numerical results for the relativistic corrections have been obtained by numerical integration of the collision term of the Boltzmann equation. The fitting is carried out for the ranges 0.02 < theta_{e} < 0.05 and 0 < X < 20, where theta_{e} = k_{B}T_{e}/m_{e}c^{2}, X = omega/k_{B}T_{0}, T_{e} is the electron temperature, omega is the angular frequency of the photon, and T_{0} is the temperature of the cosmic microwave background radiation. The accuracy of the fitting is generally better than 0.1%. The present analytic fitting formula will be useful for the analyses of the thermal Sunyaev-Zel'dovich effect for high-temperature galaxy clusters.

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arXiv1998

Relativistic Corrections to the Sunyaev-Zel'dovich Effect for Clusters of Galaxies. II. Inclusion of Peculiar Velocities

We extend the formalism of the relativistic thermal Sunyaev-Zel'dovich effect to the system moving with a velocity beta (= v/c) with respect to the cosmic microwave background radiation. In the present formalism, the kinematic Sunyaev-Zel'dovich effect for the cluster of galaxies with a peculiar velocity is derived in a straightforward manner by the Lorentz boost of the generalized Kompaneets equation. We give an analytic expression for the kinematic Sunyaev-Zel'dovich effect which is valid up to O(beta^{2}) with the power series expansion approximation in terms of theta_{e} = k_{B} T_{e}/ mc^{2}, where T_{e} and m are the electron temperature and the electron mass, respectively. It is found that the relativistic corrections to the kinematic Sunyaev-Zel'dovich effect are significant. For a typical electron temperature 10keV, one obtains -8.2% and +1.3% corrections from the O(beta theta_{e}) and O(beta theta_{e}^{2}) contributions, respectively. The O(beta^{2}) correction is extremely small, +0.2% for beta=1/300 at 10keV. Therefore it can be safely neglected. These relativistic corrections are directly reflected on the determination of the peculiar velocity of the cluster of galaxies with the observation of the kinematic Sunyaev-Zel'dovich effect.

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arXiv1998

Relativistic Thermal Bremsstrahlung Gaunt Factor for the Intracluster Plasma. II. Heavy Elements

We calculate the relativistic thermal bremsstrahlung Gaunt factor for the high-temperature plasma which exists in clusters of galaxies. We calculate the Gaunt factor by employing the Bethe-Heitler cross section corrected by the Elwert factor. The calculations in this paper are made for the fully ionized plasma for the following cases: Z = 10 (Ne), 12 (Mg), 14 (Si), 16 (S), 26 (Fe). We also calculate the Gaunt factor by using the Coulomb-distorted wave functions for nonrelativistic electrons following the method of Karzas and Latter. By comparing the Gaunt factors calculated by these two different methods, we carefully assess the accuracy of the calculation. We present the numerical results in the form of tables.

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arXiv1998

Relativistic Thermal Bremsstrahlung Gaunt Factor for the Intracluster Plasma

We calculate the relativistic thermal bremsstrahlung Gaunt factor for the high-temperature plasma which exists in clusters of galaxies. We calculate the Gaunt factor by employing the Bethe-Heitler cross section corrected by the Elwert factor. We also calculate the Gaunt factor by using the Coulomb-distorted wave functions for nonrelativistic electrons following the method of Karzas and Latter. By comparing the Gaunt factors calculated by these two different methods, we carefully assess the accuracy of the calculation. We present the numerical results in the form of tables.

astro-ph↗

arXiv1998

Relativistic Corrections to the Sunyaev-Zel'dovich Effect for Clusters of Galaxies

We study the generalized Kompaneets equation (kinetic equation for the photon distribution function taking into account the Compton scattering by electrons) using a relativistically covariant formalism. Using the generalized Kompaneets equation, we derive an analytic expression for the Sunyaev-Zel'dovich effect, which takes into account up to O(theta**5) terms, where theta=kT/mc**2 is the relativistic expansion parameter and T is the electron temperature. We carefully study the applicable region of the obtained analytic expression by comparing with the result of the direct numerical integration. We conclude that the present analytic expression can be reliably applied to the calculation of the Sunyaev-Zel'dovich effect for kT < 15keV, which is the highest electron temperature in the presently known clusters of galaxies. Therefore, the present analytic expression can be applied to all known clusters of galaxies.

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