Early photoionization of the intergalactic medium is discussed in a nearly model-independent way, in order to investigate whether early structures corresponding to rare Gaussian peaks in a CDM model can photoionize the intergalactic medium suuciently early to appreciably smooth out the microwave background uctuations. We conclude that this is indeed possible for a broad range of CDM normalizati...

A simple analytical model for estimating the fraction (Ωgas) of matter in gaseous form within the collapsed dark matter (DM) haloes is presented. The model is developed using (i) the Press-Schechter formalism to estimate the fraction of baryons in DM haloes, and (ii) the observational estimates of the star formation rate at different redshifts. The prediction for Ωgas from the model is in broad...

We utilize the principle of conservation of energy in a model which explains the cosmological redshift, Olbers’ paradox and the cosmic background radiation. The model is based on a hypothesis of absorption and emission of light by galactic and intergalactic matter, and a mean temperature of matter in the Universe compatible with the background radiation. We also discuss the early works of Regen...

In the current paradigm of cold dark matter cosmology, large-scale structures are assembling through hierarchical clustering of matter. In this process, an important role is played by megaparsec (Mpc)-scale cosmic shock waves, arising in gravity-driven supersonic flows of intergalactic matter onto dark matter-dominated collapsing structures such as pancakes, filaments, and clusters of galaxies....

In a gravitationally unstable universe, the structure of dark matter and galaxies, intergalactic gas and magnetic field can have severe impact on the propagation of ultra high energy cosmic rays (UHECR). The possible effects include spatial confinement and directional focusing along the supergalactic matter sheets, as well as universal re-acceleration at large scale shock fronts, and spectral m...

Dwarf galaxies (DGs) are more numerous than large galaxies. Most dwarfs in clusters are dEs, but in the field they belong mostly to late types. The importance of late-type DGs in the context of the intergalactic medium (IGM) lies in the fact that (at least some) are probably " young " galaxies forming stars for the first time. Many DGs have significant amounts of interstellar gas, they may form...

GRB afterglows close to their peak intensity are among the brightest sources in the sky. We discuss how GRB optical-to-X-ray afterglows can be used as probes of the metal enrichment of the interstellar matter in the GRB host galaxies and of the heating history of the intergalactic matter in filaments and outskirts of clusters of galaxies along the line of sight. The key points of the proposed o...

The most simple observed cases of gravitational lensing of distant quasars and galaxies by galaxies and clusters of galaxies are used to test Einstein’s theory of General Relativity and Newtonian Gravity over galactic and intergalactic distances. They extend the distance range over which Newton-Einstein Gravity has been tested by 10 orders of magnitude. Although the precision of the tests are f...

Deep surveys have recently discovered galaxies at the tail end of the epoch of reionization. In the near future, these discoveries will be complemented by a new generation of low-frequency radio observatories that will map the distribution of neutral hydrogen in the intergalactic medium through its redshifted 21cm emission. In this paper we calculate the expected cross-correlation between the d...

Abstract. We present a brief review of the polarization properties of the cosmic microwave background in dark matter models for structure formation. Quite independently of the model parameters, the polarization level is expected to be ∼ 10% of the anisotropy signal at angular scales ≤ 1. Detections of polarization at larger angular scales would provide a strong evidence in favour of an early re...