On the evolution of Lyman alpha clouds based upon the Minihalo model

Intergalactic clouds confined by the gravity of cold dark matter (CDM), the so called mini-halo, is considered. Assuming a simplified evolution law of UV flux and mass function of gas clouds, number density evolution and H1 column density distribution can be reproduced by mini-halo model. Considering interaction between supersonic flow and a mini-halo, spatial correlation and the proximity effect of Ly-alpha forest can be investigated

Ionization states of metallic absorption-line systems in continua of quasars

Ionization states of metallic absorption-line systems in continua of quasars (QSO's) are studied, assuming that the metallic lines arise in gaseous halos of high-redshift galaxies in photoionization equilibrium under the background UV radiation, and constraints on the intensity and spectral shape of the UV radiation are obtained. Then a structure of absorbers suitable for all of the metallic absorption line systems are discussed

The disk-halo connection and the nature of the interstellar medium

Some results on the nature of the interstellar medium that are specifically concerned with the disk-halo interaction are discussed. Over the last five years or so it has become clear that the supernovae rate in our Galaxy is spatially clumped and the consequences of such clumping are superbubbles and supershells fed by tens or hundreds of supernovae per shell. These objects evolve and expand rapidly and soon break out of the disk of the Galaxy, feeding the halo with very significant mass, energy, and momentum. As cooling occurs, gas will rain down onto the disk of the Galaxy completing the cycle. The basic flow of physical quantities from disk to halo and vice versa are discussed. Some of the many implications are noted including aspects of dynamo theory, quasar absorption lines, the theory of galactic coronae, and the nature of the x ray background. The essential difference here with the McKee-Ostriker (1977) theory is that the filling factor of the hot gas in the disk is significantly less than unity

The Ionization and Abundance of C and Si in QSO absorbers

We have analyzed high resolution data of absorption lines of Si and C in the absorption systems observed in the spectra of QSOs, in order to study the ionization state and the overabundance of Si with respect to C in the absorbers and also to study the change in these properties with redshift. No correlation is found between column density ratios of Si IV to C IV of intervening systems and redshift. The data do not provide any evidence for an abrupt change in the values of the ratio at any particular redshift unlike that for Lyman alpha forest clouds. We have compared the observed ratios of column densities of Si II and Si IV and of Si IV and C IV in different classes of absorption systems with predictions of photo ionization models for different shapes of the background radiation field. Overabundance of Si over C can be ruled out in several of the intervening systems for any shape of the background radiation. For these systems we can also rule out any contribution from the stellar sources to the background, which is then entirely from the AGNs. No overabundance is needed in other intervening systems if the radiation field from stellar sources contributes significantly to the UV background. Overabundance is, however, present in Lyman alpha forest clouds at redshifts larger than 3 and in systems associated with the QSOs. For all the intervening systems a minimum of 10 % of the background is contributed by the AGNs.Comment: To be published in Pub.Astr.Soc.Japan, 3 figure

Globular cluster formation triggered by the initial starburst in galaxy formation

We propose and investigate a new formation mechanism for globular clusters in which they form within molecular clouds that are formed in the shocked regions created by galactic winds driven by successive supernova explosions shortly after the initial burst of massive star formation in the galactic centers. The globular clusters have a radial distribution that is more extended than that of the stars because the clusters form as pressure-confined condensations in a shell that is moving outward radially at high velocity. In addition the model is consistent with existing observations of other global properties of globular clusters, as far as comparisons can be made.Comment: 8 pages, 1 figure. The Astrophysical Journal (letters), in pres

池内了先生の講演

池内了先生の講

Formation of intermediate-mass black holes in circumnuclear regions of galaxies

Recent high-resolution X-ray imaging studies have discovered possible candidates of intermediate-mass black holes with masses of M_\bullet \sim 10^{2-4} \MO in circumnuclear regions of many (disk) galaxies. It is known that a large number of massive stars are formed in a circumnuclear giant H {\sc ii} region. Therefore, we propose that continual merger of compact remnants left from these massive stars is responsible for the formation of such an intermediate-mass black hole within a timescale of $\sim 10^9$ years. A necessary condition is that several hundreds of massive stars are formed in a compact region with a radius of a few pc.Comment: 11 pages, PASJ in pres