In currently popular cosmological scenarios – all variants of the cold dark matter (CDM) cosmogony – some time beyond a redshift of 15, stars within the numerous small halos that condense with virial temperatures ∼ 10 K created the first heavy elements; these protogalactic systems, together perhaps with an early population of mini-quasars, generated the ultraviolet radiation and mechanical ener...

We analyze the Ginga LAC and Einstein SSS spectra of four cooling flow clusters, A496, A1795, A2142 and A2199, each of which shows firm evidence of a relatively cool component. The inclusion of such cool spectral components in joint fits of SSS and LAC data leads to somewhat higher global temperatures than are derived from the high energy LAC data alone. We find little evidence of cool emission...

To elucidate the effects of the UV background radiation on the collapse of pregalactic clouds, we implement a radiation-hydrodynamical calculation, combining onedimensional spherical hydrodynamics with an accurate treatment of the radiative transfer of ionizing photons. Both absorption and scattering of UV photons are explicitly taken into account. It turns out that a gas cloud contracting with...

We use a combination of high resolution N–body simulations and semi–analytic techniques to follow the formation, the evolution and the chemical enrichment of cluster galaxies in a ΛCDM Universe. We model the transport of metals between the stars, the cold gas in galaxies, the hot gas in dark matter haloes, and the intergalactic gas outside virialized haloes. We have compared three different fee...

Here we investigate an exemplary chemodynamical evolutionary simulation of a dwarf irregular galaxy. By means of this model we demonstrate the existence of three gas mixing cycles: 1) An inner local cycle mixing the metals produced in stars locally, and 2) an outer galactic cycle on which hot gas is driven out of the galaxy by multiple supernovae type II and mixes on a short timescale with the ...

The astrophysical processes that led to the formation of the first seed black holes and to their growth into the supermassive variety that powers bright quasars at z ∼ 6 are poorly understood. In standard ΛCDM hierarchical cosmologies, the earliest massive holes (MBHs) likely formed at redshift z ∼ > 15 at the centers of low-mass (M ∼ > 5×10 M⊙) dark matter “minihalos”, and produced hard radiat...

Mounting evidence from x-ray observations reveals that bound objects should receive some form of energy in the past injected from non-gravitaional sources. We report that an instantaneous heating scheme, for which gases in dense regions were subjected to a temperature jump of 1keV at z = 2 whereas those in rarified regions remained intact, can produce bound objects obeying the observed mass-tem...

Star formation may take place in a variety of locations in interacting systems: in the dense core of mergers, in the shock regions at the interface of the colliding galaxies and even within the tidal debris expelled into the intergalactic medium. Along tidal tails, objects may be formed with masses ranging from those of super-star clusters to dwarf galaxies: the so-called Tidal Dwarf Galaxies (...