The infall model of the rotation of spiral galaxies predicts that the morphology of their velocity profiles and the relative abundance of dark matter (DM) in the intermediate region between, roughly, 3 and 5 scale lengths of their exponential disks is the result of the adiabatic contraction of the cores of their DM halos due to the dissipative infall of the gas destined to form the visible core of the galaxies. We compare the model with a few observations in a plane defined by two independent variables that can be calculated for the model and the observations. The model predicts substantially more DM interior to the optical radii of the galaxies than is allowed by the “maximum disk” hypothesis (i.e. the inner circular velocity is almost entirely due to the disk matter. However, a different version of the “maximum disk” idea might agree with the model: see the discussion by E. Athanassoula in these Proceedings). An analysis of the observations that is independent of this hypothesis indicates DM in abundance that agrees with the model. The data sample, unfortunately, is too small to draw yet any definitive conclusion on the validity of the model

The Hubble expansion rate measured in the short distance scale varies from 70–75 to 90 km s−1 Mpc−1 as the kinematic distance (corrected for in fall velocity toward Virgo) increases from Dv = 200–400 km s−1 to Dv ∼ 1300 km s−1. It should be observed in the long scale as well (starting from a lower value), if the same methods were used in the same way. The Malmquist bias for spiral galaxies in the range Dv ≤ 1300 km s−1 is very small or null. The velocity distribution of galaxies in the nearest groups compared with models of various rms velocity dispersions, suggests that at small distance, dispersions of 100 km s−1 or more do not fit the observations. The effect of the deceleration due to the mass of the Local Group on the very nearby velocity field is negligible beyond 2.5–3 Mpc. The low local value of Ho extends approximately over ∼ 6–7 Mpc.

Several tests can be made to get a rough idea of the Malmquist effect in a given set of galaxies. They are : (1) The progressive loss of late types pirals (Scd or later), of low luminosity classes, of objects with small rotation velocity, or small internal dispersion, as we go to larger distances. (2) The variation of the slope of the Tully-Fisher relation, of the Faber-Jackson relation or of the Λ index with distance (differential bias).

Consider an hydrostatic self-gravitating sphere. The gravitational field is generated by 2 components: a visible (o) and an unseen (x). The resolution of the equations yields global quantities such as the mass (observed, unseen or total) of matter in the configuration Mo,x,t the ratio of unseen mass to visible one R = Mx/Mo, the mean quadratic velocity computed on the configuration V2o,x, Cv=V2x/V2o the relative concentration indicator of kinetic energy, and the relative concentration indicators of x-matter and x-potentiel energy Ci and Cx.

The purpose of this poster is to draw attention to the recent papers of Cowsik and Ghosh (J.A.A. 7, 7, 1986 et seq. and Ap.J., 317, 26, 1987) where particles of dark matter, stars and galaxies are treated as collissionless gasses. The encounterless Boltzmann equations become coupled through the common gravitational potential in which they move. Assuming that the distributions have the Maxwellian or generalised Schwarzschild form, the potentials ϕg, ϕv due to the baryonic and dark matter are shown to satisfy the coupled equations:

Fall and Rees have suggested that thermal instability in the collapsing gas of a protogalaxy gives rise to cool clouds embedded in a hot medium. They argue that the temperature of the clouds cannot fall below 104K, since metals and molecular coolants are absent. Clouds with masses exceeding 106M⊙ are gravitationally unstable and are identified as the precursors of globular clusters. This model has difficulty in explaining high-metallicity globular clusters, since metals provide cooling down to ∼102K or below, thus considerably reducing the cloud Jeans mass. The same problem arises if H2 cooling occurs.

We consider two density perturbation modes with significantly different length scales λ and L (λ ≪ L) in a homogeneous Universe within Newtonian approximation. For the two modes the coupling terms in the corresponding Euler-Lagrange and Poisson equations are taken into account within lowest order of approximation. We assume that the λ - nods (high-frequency mode) is superimposed on the large-scale mode in such way that by an appropriate averaging procedure, the global behaviour is determined only by the single L-mode. Locally (Δ x ≈ λ ≪ L) the space dependence of the L-mode can be neglected in comparison with the λ -mode, but its time evolution remains important for the evolution of the λ -mode perturbation δ. We obtain for δ the equation: where , b is the sound velocity with respect to the undisturbed homogeneous natter distribution, H is the Hubble parameter, .

The most stringent constraint against baryonic dark matter is provided by primordial nucleosynthesis. Agreement between theory and observations is reachedonly for a limited range of the baryon-to-photon ratio ‘LR, namely , which implies that, in standard cosmological frameworks, the universe cannot be closed by baryons.

Path integrals may be used to describe the statistical properties of a random field such as the primordial density perturbation field. In this framework the probability distribution is given for a Gaussian random field subjected to constraints such as the presence of a peak of given curvature at a specific location in the initial conditions. An algorithm has been constructed for generating samples of a constrained Gaussian random field on a lattice using Monte Carlo techniques. The algorithm is equivalent to, but much faster than, generating unconstrained random samples repeatedly until a sample is found satisfying the desired constraints to arbitrary precision. The method makes possible a systematic study of the density field around peaks or other constrained regions in the biased galaxy formation scenario and it is effective for generating initial conditions for N-body simulations with rare objects in the computational volume.

Shock waves from supernova explosions in early stellar generations are likely to play an important role as a feedback mechanism in all models of galaxy formation. In particular in the explosive scenario, where the large scale distribution of galaxies is attributed to fragmentation of cooling gas in huge shocks expanding in a homogeneous medium.

We reconsidered the timing problem of the neutrino-dominated cosmological scenario, i.e. the inferred young age for the large-scale structure versus the observationally indicated older age of galaxies and quasars. It can be resolved by 4 anti-biasing: of galaxy formation. By applying a variety of alternative prescriptions for galaxj formation to N-body simulations of the neutrino scenario, we find that the clustering of galaxies could be suppressed relative to the neutrinos to an extent that eliminate} the timing problem. It requires that galaxies form preferentially in the flat Sheets relative to the denser ‘filaments’ and compact clusters. This could emerge eithe from differences in the efficiency of galaxy formation itself, or due to feedback influence from a first generation of objects (e.g. quasars) which suppress the formatio: of incipient galaxies locally. Such an effect could be due to radiation pressure b Lα trapping in the ionized region at the vicinity of a quasar. We simulated various examples in order to quantify the requirements from such anti-biasing mechanisms and investigated their physical plausibility. Other aspects of the neutrino cosmology were studied in view of the proposed anti-biasing, concluding that we see no fata flaw in this picture.

This paper shows that the Kadomtsev -Petvlashvili equation of type I governs the evolution of certain weakly nonlinear fluctuations on a staticor very slowly varying cosmological background. The model consists of a mixture of nonrelativistic, collisionless (here after called “dark”) matter at nonzero temperature together with a smaller amount of zero-temperature rotation- free dust. The two components are coupled only by gravitational forces.

In the present poster, we first address theoretically the problem of gravitational amplification by extended density fluctuations and then compare statistically our new predictions to actual samples of galaxies and QSOs.

A noticeable fact about the giant luminous arcs, which have been detected in a few high-redshift clusters of galaxies (see contributions by Petrosian and by Mellier in this volume), is that they seem to be segments of almost perfectly circular rings – in one case spanning about one third of a circle. If this is a characteristic property of these arcs, they cannot be segments of randomly-oriented three-dimensional rings, which, when viewed from a random direction, should look acircular in most cases. Perhaps the most generic source for a circular ring is a limb-brightened luminous shell – as in planetary nebulae and supernova remnants. Such shells can naturally arise, for example, from explosion-generated shocks which cooled and fragmented into stars. If the sources are shells, and the arcs are either resolved or their thickness is determined by the seeing conditions (and by the CCD pixle size), there is a very general upper-limit on the possible surface-brightness contrast between the arcs and the regions encompassed by them. For the detected arcs, without any special finetuning, this limit is ≃ 3. It might become twice as big if the shell is transparent and the interior is opaque. This limit could exclude the shell model if the preliminary claims for a detected contrast greater than 10 are confirmed. It is interesting to note that the famous ring nebula presents a similar problem. We checked several mechanisms, such as stimulated radiation, which could, in principle, enhance the observed contrast while retaining the spherical symmetry; if such a mechanism is responsible for the enhanced contrast, it should show clear imprints on the spectrum. The figure shows the surface-brightess profile for a shell of thickness d.

This sample is a small one, typically 20 galaxies with z > 1, is radio flux limited and contains the most distant galaxies we presently know. Gravitational lensing by foreground galaxies and clusters of galaxies may enhance the luminosity of these galaxies by several magnitudes in both optical and radio wavelenghts. Moreover this flux limited sample should have a disproportionate number of gravitationaly amplified objects specifically because their radio fluxes are very close to the 10 Jy detection limit. When considering the spatial distribution of the 3CR galaxies with z > 1 it is found that many cases exist in which a 3CR galaxy is located near the center of a rich cluster of galaxies and/or with a foreground galaxy projected within a few arcseconds. These instances are strongly suggestive that gravitational lensing effects are likely to be present (see Hammer et al., 1986, Astr. Astroph., 169, LI, Le Fèvre et al., 1987, Nature, 326, 268). Moreover, it is not well established that these galaxies are the progenitors of lower redshift ellipticals and radio-galaxies and that they can be compared for galaxy evolution tests.

Cosmic strings would be cosmologically interesting if they acted as seeds for rich cluster and galaxy formation. Most comological scenarios require the mean mass density per unit length of the string μ to be ∼ 2 × 10−6 for cosmic strings to act as seeds. If there is a population of long-lived cosmic strings which are either long loops or infinite strings, then they will gravit ationally lense background sources (Vilenkin 1984). We are undertaking a substantial survey for multiply imaged optical quasars. So far we have examined ∼ 2500 quasars and have no candidate multiply imaged quasars with separations ≳ 13″ (Webster et aJ. 1987). This sample will double over the next year. The survey will detect multiply imaged quasars with the image separations predicted if one has a population of cosmic strings with μ ∼ 2 × 10−6 acting as gravitational lenses. In due course, this survey will enable us to confirm or rule out the possibility that cosmic strings seed galaxy formation.

A class of compact objects with cosmological density ƍ leads to a probability for multiple imaging by gravitational lensing of roughly P ≈ ƍ/ƍc, where ƍc is the critical density.

The great amount of unseen dynamical matter in large scale structures is derived from: the Newton's law of inertia and the theory of gravitation. But none of these law has been tested on scale larger than r > 10Kpc. It is then tempting to modify them following: where g(x) is a phenomenological function.