Clustering of galaxies at high redshifts

Recent observations show a large concentration of galaxies at high redshift. At first sight, strong clustering of galaxies at high redshifts seems to be in contradiction with the models of structure formation. In this paper we show that such structures are a manifestation of the strong clustering of rare peaks in the density field. We compute the frequency of occurrence of such large concentrations of galaxies in some models of structure formation.     

On the physical connections between galaxies of different types

Galaxies can be classified in two broad sequences which are likely to reflect their formation mechanism. The 'main sequence', consisting of spirals, irregulars and all dwarf galaxies, is probably produced by gas settling within dark matter haloes. We show that the sizes and surface densities along this sequence are primarily determined by the distributions of the angular momentum and formation time of dark haloes. They are well reproduced by current cosmogonies provided that galaxies form late, at z  ≲ 2. In this scenario, dwarf ellipticals were small 'discs' at z  ∼ 1 and become 'ellipticals' after they fall into cluster environments. The strong clustering of dwarf ellipticals is then a natural by-product of the merging and transformation process. The number of dwarf galaxies predicted in a cluster such as Virgo is in good agreement with the observed number. On the other hand, the 'giant branch', consisting of giant ellipticals and bulges, is probably produced by the merging of disc galaxies. Based on the observed phase-space densities of galaxies, we show that the main bodies of all giant ellipticals can be produced by dissipationless mergers of high-redshift discs. However, high-redshift discs, although denser than present-day ones, are still not compact enough to produce the high central phase-space density of some low-luminosity ellipticals. Dissipation must have occurred in the central parts of these galaxies during the merger which formed them.     

Comparison of the SFI peculiar velocities with the IRAS 1.2-Jy gravity field

We present a comparison between the peculiar velocity fields measured from a recently completed l -band Tully–Fisher survey of field spirals (SFI) and that derived from the IRAS 1.2-Jy redshift survey galaxy distribution. The analysis is based on the expansion of these data in redshift space using smooth orthonormal functions, and is performed using low- and high-resolution expansions, with an effective smoothing scale which increases almost linearly with redshift. The effective smoothing scales at 3000 km s⁻¹ are 1500 and 1000 km s⁻¹ for the low- and high-resolution filters. The agreement between the high- and low-resolution SFI velocity maps is excellent. The general features in the filtered SFI and IRAS velocity fields agree remarkably well within 6000 km s⁻¹. This good agreement between the fields allows us to determine the parameter β = Ω^0.6 / b , where Ω is the cosmological density parameter, and b is the linear biasing factor. From a likelihood analysis on the SFI and IRAS modes we find that β = 0.6 ± 0.1, independently of the resolution of the modal expansion. For this value of β, the residual fields for the two filters show no systematic variations within 6000 km s⁻¹. Most remarkable is the lack of any coherent, redshift-dependent dipole flow in the residual field.     

Proper motions and variability of the H2 knots in the HH 111 and 121 protostellar outflows

We discuss the formation of spectral features in the decelerating ejecta of gamma-ray bursts, including the possible effect of inhomogeneities. These should lead to blueshifted and broadened absorption edges and resonant features, especially from H and He. An external neutral ISM could produce detectable H and He, as well as Fe X-ray absorption edges and lines. Hypernova scenarios may be diagnosed by Fe Kα and H Lyα emission lines.     

Angular fluctuations in the cosmic microwave background owing to initial perturbations in the radiation temperature

A new method is proposed to account for multiple scattering by electrons in calculations of the correlation functions describing the angular fluctuations in the cosmic microwave background radiation (CMBR). The apparatus of the theory of radiative transport with Rayleigh scattering is used. The problem is reduced to solving an integral equation for the vector source function (dependent only on time), along with differential equations for the other quantities (scalar potentials, baryon velocities, etc.) which show up in the problem. The quantities which describe the angular fluctuations in the CMBR (in the temperature and in the polarization) are then calculated by integrating the vector source function along the line of sight. As an illustration, the correlation functions and power spectra are calculated for the case where the fluctuations are produced by some initial gaussian perturbations of the CMBR. __________ Translated from Astrofizika, Vol. 50, No. 4, pp. 621–631 (November 2007).