Satoru Ikeuchi

Formation of Hot Intergalactic Gas by Gas Ejection from a Galaxy in an Early Explosive Era

Chemical evolution of a galaxy in an early explosive era is studied by means of one zone model. Calculating the thermal properties of interstellar gas and the overlapping factor of expanding supernova-remnant shells, the gas escape conditions from a galaxy are examinxad ed. From these, it is shown that the total mass of ejected gas from a galaxy amounts to 10~40% of the initial mass of a galaxy. The ejected gas extends to the intergalactic space and the whole universe. The mass, the heavy-element abundance and other physical proxad perties of thus formed intergalactic gas are investigated for various parameters of galactic evolution. Some other effects of gas release on the evolution of a galaxy and the evolution of the universe are discussed.

Formation of Elements in Neutron Rich Ejected Matter of Supernovae

The thermal and chemical properties of neutron rich- ejected matter of supernovae are investigated from the high-temperature stage (T~s X 1010 K) to the low-temperature stage (T~3.2X 109 K) under an appropriate assumption for the expansion law. We have taken into account changes of the entropy and of the electron mean molecular weight due to beta process, which ani essentially different from previous relevant works. The initial n/p ratio is deterxad mined by the chemical equilibrium between neutrons, protons and leptons when the matter is opaque to electron neutrinos, whereas it is given by a steady state condition in the case that the matter is transparent. Considering reactions by nucleon weak interaction, nuclear statistical equilibrium and nuclear beta decays, the initial conditions for the rprocess such as the abundances of seed nuclei, the neutron flux and the density of the matter are obtained for various expansion speeds and initial n/p ratios. It is shown that the entropy production and the decrease of mean molecular weight of the electron due to the beta process play an important role, and found that in the cases of slow expansion, neutrons are exhausted due to fast nuclear beta decays before the r-process proceeds, whereas in the cases of fast expansion and/or with the large initial. n/p ratios, a sufficient amount of free neutrons are left for r-process. Finally the dynamic r-process is discussed on the basis of our numerical results.

Dynamical Collapse of the Intracluster Gas and the Formation of a Hot Plasma in Clusters of Galaxies

Dynamical collapse of the intracluster gas in clusters of galaxies is studied numerically by taking account of both the gravity of background galaxies and the self-gravity. The adiabatic case, the case with the thermal bremsstrahlung cooling and the case with both the heat conduction and thermal bremsstrahlung cooling have been calculated. In the first two cases, a hot plasma which is formed after the bounce reaches an equilibxad rium state if the initial density po is lower than a certain critical value. In the last case, the gas secularly contracts. The results are compared with X-ray observation of the Coma cluster.

Collective Instabilities of Self-Gravitating Systems. III Disk-Halo System

The instability modes of the infinitesimally thin self-gravitating disk, which is composed of rotating and non-rotating parts, are investigated. By solving the dispersion relation numerically under various physical situations, two growing modes are found. They are the modified Jeans mode of rotating component or non-rotating one and the Landau mode by wave-particle (non-rotating component) interactions. Possible relevances to spiral arms are discussed briefly.

Hydrostatic Structure of a Hot Plasma in a Cluster of Galaxies

Hydrostatic equilibrium solutions for the hot gas in a cluster of galaxies have been studied assuming the polytropic relation. The final equilibrium state is related to the initial state of the gas in the cluster using the mass and energy conservation laws between the above two states. Results are applied to the X-ray source in Coma cluster. We have obtained the central temperature, the central density and the mass of the intracluster gas such as 1.8X10 OK, 2.8X10- 27 gm/cm and 5.7X101vf0, respectively. As for the X-ray emission mechanism of these sources, inverse compton and thermal bremsstrahlung theories have been proposed. However, recent spectral analyses of soft X-ray data2l tend to show a strong preference for the thermal model. Moreover, tailed radio sources3l and the excess of SO galaxies4l found in these clusters may be well interpreted, if hot intracluster gases exist. Concerning the thermal model, a wind model, sl infall models6l, 7) and static modelsn,sl have been studied. Lea8l has calculated the hydrostatic equilibrium soluxad tion for a polytropic gas in a cluster of galaxies under the boundary condition that the temperature of the gas approaches to zero at infinity. By comparing that solution with observations for the Coma cluster, she shows that the intracluster gas is distributed more widely than the galaxies by a factor of about 2--2.5 and the temperature of the gas given from a best-fit model is 1.5 X 108 oK. Takahara et al. 9l have investigated the dynamical collapse of gas in a cluster of galaxies. As a result of numerical calculations, they find that a hot plasma is formed after the bounce and it attains an equilibrium state. In § 2 the hydrostatic equilibrium solution for a polytropic gas in a cluster of galaxies is derived. In § 3 the hydrostatic equilibrium state which is attained after the dynamical collapse is discussed using the energy and mass conservation laws which relate the final state of the gas to the initial state. In § 4 the central temperature, the central density and the mass of the intracluster gas are obtained

Thermal Properties of Self-Gravitating Plane­ Symmetric Configuration

11 They showed that the pressure and density distributions of polytropic disk-shape stars are analytically described in terms of the incomplete beta functions. Moreover, the pressure at the plane of symmetry depends only on the surface density, i.e., mass contained in a cylinder with a unit area. These properties of the disk-shape stars are essentially different from spherically symmetric stars. DynaJTtical collapse of the disk-shape stars vas studied by Kusaka. 21