The early reionization of the intergalactic medium, which is favored from the WMAP temperature-polarization cross-correlations, contests the validity of the standard scenario of structure formation in the cold dark matter cosmogony. It is difficult to achieve early enough star formation without rather extreme assumptions such as very high escape fraction of ionizing photons from proto-galaxies ...

New X-ray observations of the sparse NGC 3258 group of galaxies made by the ASCA satellite with good spectral and spatial resolution has revealed that this group has a gravitational potential deep enough to prohibit significant mass removal from the system. The baryonic fraction within 240h 50 kpc is found to be 0.065 −0.020 for h50 = 1, where h50 ≡ H0/50 km s Mpc, in good agreement with the un...

While the average metallicity of the intergalactic medium rises above Z & 10Z⊙ by the end of the reionization, pockets of metal-free gas can still exist at later times. We quantify the presence of a long tail in the formation rate of metalfree halos during late stages of reionization (redshift z ≈ 6), which might offer the best window to detect Population III stars. Using cosmological simulatio...

We study the impact of outflows driven by active galactic nuclei (AGN) on galaxy formation. Outflows move into the surrounding intergalactic medium (IGM) and heat it sufficiently to prevent it from condensing onto galaxies. In the dense, high-redshift IGM, such feedback requires highly energetic outflows, driven by a large AGN. However, in the more tenuous low-redshift IGM, equivalently strong ...

We summarise the science cases for an ELT that were presented in the parallel session on the intergalactic medium, and the open discussion that followed the formal presentations. Observations of the IGM with an ELT provides tremendous potential for dramatic improvements in current programmes in a very wide variety of subjects. These range from fundamental physics (expansion of the Universe, nat...

The isotropy in the ultra high energy cosmic ray (UHECR) flux observed by Yakutsk and AGASA experiments, is a very strong constraint to production and propagation models alike. Most of the scenarios proposed in the literature should produce a sizable anisotropy as either extragalactic luminous or dark matter is normally associated with the invoked particle sources. We explore the possibility th...

We study the gravitational wave emission from the first stars which are assumed to be Very Massive Objects (VMOs). We take into account various feedback (both radiative and stellar) effects regulating the collapse of objects in the early universe and thus derive the VMO initial mass function and formation rate. If the final fate of VMOs is to collapse, leaving very massive black hole remnants, ...

The pair-production absorption of high-energy -rays by intergalactic low-energy photons is expected to produce a high-energy cuto in the spectra of sources which is a sensitive function of redshift. We rst discuss the expected absorption coe cient as a function of energy and redshift derived by Stecker and De Jager by making use of a new empirically based calculation of the spectral energy dist...

We use the observed number and column-density distributions of intergalactic O VI absorbers to constrain the distribution of metals in the low-redshift intergalactic medium (IGM). In this simple model the metals in the O VI absorbers are assumed to be produced in and propagated from lowredshift galaxies drawn from a real sample, in this case the Sloan Digital Sky Survey (SDSS). This model can e...