The problem of volume test, V/Vm, in zero pressure and matter dominated Friedmann universe model is explored under various values of deceleration parameter qo. The following conclusions are drawn. (i) For different values of qo, the change of V/Vm is sensitive at small values of z. Since values of V/Vm are very small at small values of z, this change exerts little effect on the average values of V/Vm. (ii) when values of z and zm are fixed for each member of a sample, large values of qo yield larger values of V/Vm, especially in the case of large z. (iii) For qo<1, the method of volume test is reliable. When qo>2, especially qo>3, this method has to be used with caution at large z.

CCD direct imaging of fields around quasars is used as a method for locating galaxy clusters and groups associated with quasars. Average galaxy counts in the sky obtained from control fields are used to correct for background galaxies in the quasar fields. This correction allows one to derive the luminosity function (LF) of the associated galaxies at the redshifts of the quasars. It is demonstrated that using the derived LF and average galaxy count data, self-consistent models of the evolution of the LF and galaxy counts can be obtained. Current data are best fitted, with a large uncertainty, by a qo between 0.0 and 0.5 and an evolution in M* of −0.9±0.5 mag. It is found that the average environment of radio-loud quasars at z∼0.6 is about three times richer in galaxies than that of quasars at z∼0.4.

The merits of selecting samples of quasars for statistical analysis on the basis of optical variability is discussed. Samples selected this way are essentially uncontaminated by spurious objects, and contain no serious redshift biasses. A preliminary sample from a long term survey suggests a timescale of variation for quasars of about four years, and indicates a fall off in numbers at around B = 20.

Much of the optical and ultraviolet radiation of bright quasars may originate in a massive accretion disk around a central black hole. Most searches for the signature of such disks gave ambiguous results but lately there are new ideas that may lead to their discovery. In particular, the apparent brightness of thin disks depend on their inclination to the observer's line of sight and this may be detected by the equivalent width of some emission lines (Netzer 1985, 1986). This idea may change our view on the inner structure of quasars and other AGN. In addition, it points to a potential selection effect that has not been taken into account so far. Magnitude limited optical quasar samples may contain, preferentially, face-on disks, thus cosmological evolution based on such samples may be biased. There are other implications, especially to the observed correlation of Lop with Lx in quasars.

The observational evidence for unseen matter is briefly reviewed for objects ranging from small to very large scales. The existence of large mass discrepancies is clearly recognized in individual spiral galaxies and in rich clusters of galaxies. For other systems - dwarfs, ellipticals, binaries and groups - the results are more uncertain and still rather controversial. The data on spirals indicate values of the cosmological density parameter Ω around 0.02, those on clusters Ω ≃ 0.2. The spatial distribution of this dark matter is still largely unknown: while on the galaxy scale it must be located mainly in the outer parts of the stellar system, in clusters it is unclear whether it follows the distribution of the visible galaxies or not.

The observational evidence for the presence of dark matter is now generally accepted, with no lack of possible candidates (see e.g. Dekel, Einasto, and Rees 1986). The proposed candidates are devided into two groups, baryonic and non-baryonic. The latter is further devided to hot and cold dark matter. For the cold dark matter, among the first to be proposed is the axion. In this paper we shall not dwell on numerous cold dark matter candidates offered by particle physicists, for there are review articles on the subject (see e.g. Turner 1986, Primack 1986). The main purpose of the present report is to suggest that neutron star cooling theory and future space satellite programs (e.g. AXAF, XAO, LXAO) have a potential for offering the best astrophysical constraint on the axion mass and hence, giving valuable insight to some cosmological problems.

We show how within the theoretical framework of a Gamow cosmology with massive neutrinos, the observed correlation functions between galaxies and between clusters of galaxies, naturally lead to a “cellular” structure of the Universe. From the size of “elementary cells” we derive constraints on the value of the masses and chemical potentials of the cosmological “inos”. We outline a procedure to estimate the “effective” average mass density of the Universe. We predict also the angular size of the inhomogeneities to be expected in the cosmological black body radiation as remnants of this cellular structure. A possible relation of our model to a fractal structure is indicated.

One of the most important discoveries in modern cosmology and astrophysics is that the dark matter dominates at every scale of the Universe (Rubin et al., 1978, Forman et al., 1985, Faber and Gallagher, 1979, Sancisi, 1987). The problem that follows is to understand the components of the dark matter and to determine the physical properties of these components.

The study of gravitational lenses is intimately tied to observational cosmology. When we observe a gravitationally lensed quasar, we are viewing a single object along two or more neighboring paths (null geodesics) of cosmological dimensions (Figure 1). What we see depends on bulk properties of the universe, such as Ho and qo, on the large scale structure and inhomogeneities along the paths, and on the small scale structure in and around the primary deflector. Furthermore, the deflection of light depends on the gravitational field along the line of sight, so it is sensitive to all forms of matter: luminous or dark, baryonic or exotic. Thus the images of gravitationally lensed quasars contain an imprint of the universe that is virtually inaccessible by any other means. The hope of decoding this imprint has stimulated observers and theorists to expend many thousands of hours of telescope time, computer time and cogitation on the elucidation of gravitational lens properties.

Gravitational lens surveys are of cosmological interest because they provide a way to measure the gravitational field of both luminous and dark matter. Many of the other methods used to detect the presence of dark matter, such as studies of galaxy rotation curves and cluster dynamics, require that there be luminous objects in the gravitational field that act as tracers of the mass. This may introduce a selection effect. In constrast, in studies of gravitational lenses, the beacon we observe can be far (at distances of order one thousand Mpc) from the gravitational field. In this paper we describe a VLA survey designed to detect gravitational lensing on sub-arc second and arc second scales. We also present a preliminary result of the radio data: we find that the density of matter in the form of a uniform, comoving number density of 1011 to 1012M⊙ compact objects, luminous or dark, must be substantially less than the critical density.

3C324, a giant radiogalaxy at z = 1.206 has been suspected by us to be a gravitational lens: in a previous work, we have identified an additional line system at z = 0.845 in its spectrum. We present here new observations of 3C324 at C.F.H.T. in R broad band imaging and in adequate filters; they strongly suggest that 3C324 is the first example of a multiply imaged radiogalaxy. The 3C324 case is also a fair confirmation that gravitational lensing may well explain the overluminosity of distant radiogalaxies.

The history and current observational status of the giant gravitational lens candidate 1146+111B,C are reviewed. In the absence of any new positive evidence and in the presence of reported differences in the UV and IR spectra of B and C, the lens hypothesis is clearly much weaker than previously. Nevertheless, given the substantial similarity of the spectra over a broad range of wavelengths, discrepancies among various spectroscopic observations of C, and the possibility of spectral variability plus large differential time delays, the data do not yet support any definite conclusion as to the nature of 1146+111B,C.

Recent observations of the radio galaxy 3C 321 are presented. The optical nucleus consists of two components (A, B), separated by ∼ 4″ (∼ 6 kpc), whose low-resolution spectra strongly resemble those of high-ionization type 2 Seyfert nuclei. The relative intensities of the emission lines differ in A and B by less than 1%, and their profiles are almost identical. 3C 321 appears to be a convincing example of a gravitationally lensed object.

Careful analysis of high-quality radio and optical data, however, reveals that the system is almost certainly not a lens. The equivalent widths of the emission lines are roughly twice as high in B than in A, and there are significant spatial offsets between regions of bright continuum and line emission. A slight, but fundamental, difference is visible in the two Hα emission profiles. The radial velocities of A and B are discrepant by 31 ± 10 km s−1. Finally, component A is nearly coincident with a flat-spectrum radio core, whereas B is next to an extended, steep-spectrum knot of radio emission.

This object should serve as a warning to lens hunters: beware of impostors, whose true properties may be difficult to ascertain without extensive optical and radio observations.

Gravitational micro-lensing due to stars in the deflecting galaxy influences the brightness and the spectra of the macro-images. Thus differences in the spectra of different macro-images are not automatically an argument against gravitational lensing. Furthermore changes in the spectra due to micro-lensing may give informations on the quasar structure. From high amplification events the brightness profile of the source may be obtained. The time scale of the high amplification event is proportional to the source radius and inverse proportional to the transversal velocity. Due to the large brightness gradient by a high amplification event, a “parallax-effect” occurs, from which the transversal velocity may be obtained, and thereby the source radius (R=Δ t · VT). We roughly estimate 0.3 high amplication events per year for all gravitationally lensed quasars. Frequent monitoring should be carried out in order to predict high amplification events as early as possible.

In this paper, dark matter of Milky Way is discussed as a transparent gravitational lens. The mass distribution of Milky Way is composed of spheroid, disk and dark matter (corona). The trajectory of light ray influnced by Milky Way has been calculated numerically. The deflecting angle to a extragalactic souce is changed with different observational direction and is about several seconds in maximum. The brightness amplification ratio Kv of extragalactic background radiation is also derived from the redistribution of intensity due to the gravitational lens effects of Milky Way, ΔKv/Kv is about 10−5 in maximum. Kv has been expanding to multipole with spherical harmonics by means of Kv distribution in celestial sphere. Dipole and qudrapole are about 3×10−6 and 7×10−6 respectively, which might be added to the observational data of microwave background radiation. A measurement method to pick out the gravitational lens effects from real cosmological anisotropy has been proposed. (ref. 8)

The properties of the different types of QSO absorption systems are briefly summarized. An overview is given of the potential applications of absorption lines in cosmology. Recent work on the cosmological evolution of the different types of absorbers is discussed. The physical properties of the intergalactic medium are discussed in the light of recent work on the “Lyman alpha clouds”. The uses of the lines for studies of the evolution of clustering in the Universe are described. Recent puzzling results on common absorption in pairs of QSOs, particularly Q1037–2704 and Q1038–2712, are summarized.

A comparison between three types of intervening absorption line systems: the Lyα forest, the Lyα damped systems and the narrow metal line systems has been done for the observational properties including the frequency of the systems, the equivalent width distribution, the two point correlation function, the metal abundances, and the dN/dz vs. z behavior.

This paper presents some preliminary results from analysis of our high-resolution (30–35 km/s FWHM) spectra of the Lyman α forest region in the z = 3.78 QSO 2000-330. These spectra were obtained at the Anglo-Australian Telescope over several observing seasons and have been analysed by fitting multiple-cloud Voigt profiles to Lyman series and heavy-element absorption lines. Two specific issues are addressed here:

1. (i) The distribution of column densities, N(H I), and velocity dispersions, b, for hydrogen clouds in the interval zabs = 3.43–3.78;

2. (ii) Heavy-element abundances in a system at zabs = 3.1723.

High resolution observations of regions in the Lyα forest of QSO spectra have been obtained using the Anglo-Australian Telescope. The amount and quality of the data, and the analysis techniques used, have enabled the clustering properties of these objects to be explored on scales smaller than has previously been possible. The results suggest that the Lyα clouds are weakly clustered with <ξ> = 0.32±0.08 over the velocity range 50–290 km/s.

The new ROE/ESO large-scale AQD survey for quasars forms a connected area of ∼ 200 deg2 near the south galactic pole, and has resulted in the discovery of a total number of quasar candidates that is comparable to the number previously published from all other sources (see the poster paper by Iovino, Clowes & Shaver at this conference). In this paper we describe the first results of a three-dimensional self-clustering analysis of ∼ 1100 “high-probability” candidates occupying the assigned-redshift band of 1.8 to 2.4. Although the analysis is sensitive to very weak clustering we find no evidence that quasars are distributed in any way other than randomly. The implications of this result are discussed.