Using B, V, R, I photometric parallaxes for components of wide binaries, new bolometric corrections by Bergeron et al. (1995) and cooling curves by Wood (1995), we have determined the white dwarf luminosity function (WDLF; Oswalt et al. 1996). A minimum age of 9.5+1.1−0.8 Gyr is implied for the Galactic disk; arbitrarily old models are consistent at the +2σ level. Smith (1997) confirms these results using a much larger sample and similar methodology. Using these same new models, Wood & Oswalt (1997) show that the WDLF of Liebert et al. (1988) yields an age of 7.5+0.5−0.5 Gyr, more than 20% younger than their original estimate.

Coalescing compact binaries are the most promising candidates for detection by near-future, ground based laser interferometric detectors. It is very important to investigate detailed wave forms from coalescing compact binaries. When one (or two) of the stars is a black hole, some of those waves are absorbed by the black hole. Here, we consider a case when a test particle moves circular orbit on the equatorial plane around a Kerr black hole, and calculate the the energy absorption rate by the black hole. We adopt an analytic techniques for the Teukolsky equation which was found by Mano, Suzuki, and Takasugi (1996). We calculated the energy absorption rate to O((v/c)13) beyond the Newtonian-quadrupole formula of gravitational waves radiated to infinity, assuming v/c ≪ 1. Here v is the velocity of the particle. We find that, when a black hole is rotating, the black hole absorption appear at O((v/c)5) beyond the Newtonian-quadrapole formula. These effects become more important as the mass of the black hole becomes larger. We also found that the black hole absorption is more important when a particle moves to the same direction of the black hole rotation. All the details of this paper is presented in Tagoshi et al. (1997).

We obtained near-infrared and new deep optical images of the field near the radio-loud quasar 1335.8+2834 at z=1.086 where excess of galaxy surface number density was reported by Huthings et al. [AJ, 106, 1324]. We found a clustering of objects with very red optical-NIR color, 4 < R–K < 6 and 3 < I–K < 5 near the quasar. The colors and magnitude of the reddest objects are consistent with those predicted for luminous (> 0.5L∗) and old (2-4 Gyr old) passively evolving elliptical galaxies at z=1.1.

The CO Tully-Fisher (TF) relation is able to measure the distances to farther galaxies than the HI TF relation reaches (Sofue et al. 1997). The galaxies observed for the CO TF relation at the high redshift are often infrared luminous galaxies. The fraction of interacting galaxies is large in the infrared luminous galaxies. Therefore, first we have analyzed the CO and HI linewidths for nearby interacting galaxies in order to examine the influence of the interaction on the linewidths. We found that HI linewidths for the interacting galaxies are significantly larger than CO (Tutui and Sofue 1997a). It suggests that the influence of the interaction is smaller at the inner region of galaxies where the CO gas exists, and that the CO TF relation is more reliable tool for the galaxies which have the evidence of the galaxy interaction as well as galaxies in rich clusters.

We discuss the fragmentation of primordial gas clouds in the universe after decoupling. Comparing the timescale of collapse (tdyn) with that of fragmentation (tfrag), we obtained the minimum mass of a fragment analytically as following way.

A potential diagnostic application of molecular rotational absorption lines at high redshift is to test the invariance of physical constants. This can be done by comparing the observed redshifted frequency of a molecular absorption line with redshifted lines from other types of transitions such as the 21cm hyperfine transition or electronic resonance transitions. In order to set stringent limits, it is necessary to achieve the greatest possible frequency resolution. This makes radio lines well suited for this purpose.

The first results of observations of microlensing have discovered a phenomenon, predicted in the papers of Byalko (1969) and Paczynsky (1986). A character of the gravitational microlens is unknown till now, although the most widespread hypothesis assumes that they are compact dark objects as brown dwarfs. Nevertheless, they could be presented by another objects, in particular, an existence of the dark objects consisting of the super symmetrical weakly interacting particles (neutralino) has been recently discussed in the papers of Gurevich et al. We consider microlensing by a neutralino star in framework of a rough model which is rather clear and we obtain analytical expressions for results. We approximate the density of distribution mass of a neutralino star in formwhere r is the current value of a distant from star's center, ρo is mass density of a neutralino star for distance a0 from a center, an is a “radius” neutralino star. The detailed analysis of the model is presented in the papers of Zakharov & Sazhin (1996a, 1996b). This research has been supported in part by Russian Foundation of Fundamental Research (grant N 96-02-17434).

The observed structure of the Universe is hierarchical. Galaxies and clusters of galaxies are concentrated within elongated filamentary chains of various richness. High-density regions of the Universe form superclusters consisting of one or several clusters of galaxies and chains of galaxies surrounding and joining clusters. The space between filaments is void of galaxies. Superclusters and voids form a continuous network of alternating high- and low-density regions in the Universe.

The study of large-scale structure through QSO clustering provides a potentially powerful route to determining the fundamental cosmological parameters of the Universe (see Croom & Shanks 1996). Unfortunately, previous QSO clustering studies have been limited by the relatively small sizes of homogeneous QSO catalogues that have been available. Although approximately 10,000 QSOs are now known (Veron-Cetty & Veron 1997), the largest catalogues suitable for clustering studies contain only 500–1000 QSOs (Boyle et al. 1990, Crampton et al. 1990, Hewett et al. 1994). Even combining all such suitable catalogues, the total number of QSOs which can be used for clustering studies is still only about 2000.

Empirical studies of the Large–Scale Structure in the nearby Universe come in two complementary modes, namely the investigation of either the distribution of luminous matter or voids: (i) The description of the galaxy and cluster distribution employs correlation functions, clustering analysis, topological methods, et cetera. (ii) The investigation of the empty regions between systems of galaxies uses void probability functions, mean diameters of voids, the compilation of void catalogues, and so forth.

X-ray emission from clusters of galaxies is the most useful tool in studying mass distribution and chemical compositions in these enormously large systems. The hot intracluster medium (ICM) has been heated up to kT = 3–10 keV during the gravitational collapse, and X-ray luminosities indicate that the gas is more massive than the total galaxy mass contained in clusters by factors of 3–5. This makes ICM the dominant form of baryons in the universe. In many clusters observations indicate that ICM is in a hydrostatic equilibrium within a potential governed by the dark matter, and the cooling time is longer than the Hubble time except for the bright centers. The ICM, therefore, enables us a close look at the structure of gravitational potential. At the same time, heavy-element abundances in the ICM and their distribution are used to estimate past supernova activities and metal injection mechanism in cluster space.

ROSAT deep and shallow surveys have provided an almost complete inventory of the constituents of the soft X-ray background which led to a population synthesis model for the whole X-ray background with interesting cosmological consequences. According to this model the X-ray background is the “echo” of mass accretion onto supermassive black holes, integrated over cosmic time. A new determination of the soft X-ray luminosity function of active galactic nuclei (AGN) is consistent with pure density evolution, and the comoving volume density of AGN at redshift 2–3 approaches that of local normal galaxies. This indicates that many larger galaxies contain black holes and it is likely that the bulk of the black holes was produced before most of the stars in the universe. However, only X-ray surveys in the harder energy bands, where the maximum of the energy density of the X-ray background resides, will provide the acid test of this picture.

We probe gravitational clustering in N-body simulations using geometrical descriptors sensitive to ‘connectedness’: the genus curve, percolation and shape statistics. As gravitational clustering advances, the density field in N-body simulations shows an increasingly pronounced departure from Gaussianity reflected in the changing shape of the percolation curve and the changing amplitude and shape of the genus curve. We feel that both genus and percolation curves provide complementary probes of large scale structure topology and could be used to discriminate between models of structure formation and the analysis of observational data such as galaxy catalogs and MBR maps. The filling factor in clusters & superclusters at percolation is small indicating that matter is more likely to lie in filaments and pancakes. An analysis of ‘shapes’ in N-body simulations has shown that filaments are more pronounced than pancakes. To probe shapes of clusters and superclusters more rigorously we propose a new shape statistic which does not fit isodensity surfaces by ellipsoids (as done earlier). Instead our shape statistic is derived from fundamental properties of a compact body such as its volume V, surface area S, integrated mean curvature C, and connectivity (characterized by the Genus). The new shape statistic gives sensible results for topologically simple surfaces such as the ellipsoid, and for more complicated surfaces such as the torus.

Currently little is known about the mass distribution on intermediate scales between those probed by deep redshift surveys of galaxies and those probed by COBE. Catalogs of galaxy clusters reach depths of several hundred megaparsecs, and, thus, are very useful for those scales. Only the Las Campanas Redshift Survey (LCRS) is comparable with that depth. However, the LCRS samples only narrow slices whereas cluster catalogs cover a large fraction of the sky. Clusters seems to be the most suitable objects to fill the gap between scales probed by COBE and the galaxy samples. Moreover, clusters are advantageous over galaxies as probes of the matter distribution in the Universe because our understanding of its formation and evolution is better established than it is for galaxies. Clusters are high peaks (mass scale M ≃ 1015M⊙) in the density field, which have collapsed relatively recently. Because of that, it is easy to identify clusters in numerical simulations. But the number of clusters is much smaller than the number of galaxies, which makes the statistics of clusters noisier. Nevertheless, clusters are exceptionally useful objects for the investigation of the matter distribution on scales well above 100 h–1 Mpc. Thus, it is worth to apply different statistical tests to these objects.

In this talk, I will show how to determine the biasing factor b from the high-order moments of galaxies. The determination is based on the analytical modeling of primordial peaks and virialized halos and is independent of the currently unknown density parameter Ω0 and other cosmological parameters. The observed high-oder moments of the APM galaxies require that the biasing factor b be very close to 1, i.e. the optical galaxies are an unbiased tracer of the underlying mass distribution (on quasilinear scale). The theoretical argument can be easily generalized to the three-point correlation function and the bispectrum both of which can used as further observational tests to the important conclusion of b ≈ 1 drawn from the high-order moments. Finally I present our preliminary results of the three-point correlation functions for the Las Campanas Redshift Survey.

The three-dimensional distribution of galaxies in the redshift surveys differ from the true one since the distance to each galaxy cannot be determined by its redshift z only; for z ≪ 1 the peculiar velocity of galaxies, typically ∼ (100–1000)km/sec, contaminates the true recession velocity of the Hubble flow, while the true distance for objects at z ≳ 1 sensitively depends on the (unknown and thus assumed) cosmological parameters. This hampers the effort to understand the true distribution of large-scale structure of the universe. Nevertheless such redshift-space distortion effects are quite useful since through the detailed theoretical modeling, one can derive the peculiar velocity dispersions of galaxies as a function of separation, and also can infer the cosmological density parameter Ω0, the dimensionless cosmological constant λ0, and the spatial biasing factor b of galaxies and/or quasars, for instance. In this talk, I discuss the importance of such redshift distortion induced by the geometry of the universe, which summarizes the recent results of my collaborative work in this topic (Matsubara & Suto 1996; Nakamura, Matsubara, & Suto 1998; Magira, Matsubara, Jing, & Suto 1998).

Most of methods to determine the cosmological parameters by using the gravitational lensing are based on the following three typical observations; (1) the image separation, (2) the lensing statistics and (3) the time delay. For the accurate estimation of the cosmological parameter, it is of great importance to clarify the relation between the observation in the realistic universe and the determination of the cosmological parameters. In particular, it has been discussed by many authors that inhomogeneities of the universe may affect the cosmological tests.

We have investigated some modifications to the Press & Schechter (PS) (1974) prescription resulting from shear and tidal effects (Audit & al. 1997a). These modifications rely on more realistic treatments of the collapse process than the standard approach based on the spherical model.

This poster paper presents an extension of the entropy-driven model of cluster evolution developed by Bower, 1997 (MN, 288, 355) in order to study the evolution of clusters in a low density universe. Our approach allows us to explicitly seperate the contributions from gravitational collapse and changes in the core entropy of the intracluster gas. Here, we apply the model to determine whether a preferred value of Ω0 is selected by currently available constraints (Figure 1). Measurements of the X-ray evolution of clusters cannot, by themselves, select out a particular cosmological model. An additional constraint on the effective power spectrum index (n) is required. This can either come from a measurement of the large-scale galaxy correlation function or from the shape of the present-day temperature function. A theoretical calculation of the Ω0 dependence of the power spectrum does not help break the inherent degeneracy.

We compare the angular correlation function measured for FIRST sources (Becker et al., Cress et al.) with COBE-normalized CDM-model predictions (Cress & Kamionkowski). We note that uncertainties in the z-distribution do not affect the predictions dramatically and that the effects of non-linear evolution of the power spectrum are significant for θ<∼20′. We find the CF at larger angles to be sensitive to clustering of nearby sources. The smaller angle measurements, when combined with results from other surveys (Loan et al., Rengelink et al.) indicate that the bias required for the data to fit CDM models increases as the surveys probe deeper. We also point the reader to Refregier et al. for information on the use of weak lensing of FIRST sources in probing foreground mass.