Yasuharu Kohyama — Page 2

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.

astro-ph↗