Neutral intergalactic clouds are so greatly out numbered by galaxies that their integral HI content is negligible in comparison to that contained in optically luminous galaxies. In fact, no HI cloud that is not associated with a galaxy or grouping of galaxies has yet been identified. This points to a causal relationship that relies on gravitational potentials that bind galaxies also being respo...

First galaxies formed within halos of mass M = 107.5−109 M⊙ at z = 30−40 in the standard cold dark matter (CDM) universe may each display an extended hydrogen 21-cm absorption halo against the cosmic microwave background with a brightness temperature decrement of δT = −(100 − 150) mK at a radius 0.3 ≤ r ≤ 3.0 comoving Mpc, corresponding to an angular size of 10 − 100 arcseconds. A 21-cm tomogra...

We develop a coupled model for the evolution of the global properties of the intergalactic medium (IGM) and the formation of galaxies, in the presence of a photoionizing background due to stars and quasars. We use this model to predict the thermodynamic history of the IGM when photoionized by galaxies forming in a cold dark matter (CDM) universe. The evolution of the galaxies is calculated usin...

The amount of detected baryons in the local Universe is at least a factor of two smaller than measured at high redshift. It is believed that a significant fraction of the baryons in the current Universe is “hiding” in a hot filamentary structure filling the intergalactic space, the Warm-Hot Intergalactic Medium (WHIM). We found evidence of the missing baryons in the WHIM by detecting their sign...

The temperature (T ) and entropy (S) fields of baryonic gas, or intergalactic medium (IGM), in the ΛCDM cosmology are analyzed using simulation samples produced by a hybrid cosmological hydrodynamic/N-body code, effective capturing shocks and complex structures with high precision. We show that in the nonlinear regime the dynamical similarity between the IGM and dark matter will be broken in th...

The Arecibo H i Strip Survey probed the halos of ∼300 cataloged galaxies and the environments of ∼14 groups with sensitivity to neutral hydrogen masses ≥ 10 M⊙. The survey detected no objects with properties resembling the High Velocity Clouds (HVCs) associated with the Milky Way or Local Group. If the HVCs were typically MHI = 10 7.5 M⊙ objects distributed throughout groups and galaxy halos at...

Radio galaxies are the only non-blazar extragalactic objects detected in the VHE (E > 100 GeV) band. These objects enable the investigation of the main substructures of the AGN, in particular the core, the jet and its interaction with the intergalactic environment. Clusters of galaxies, instead, have not been detected by γ-ray observatories. These objects are collections of up to thousands of g...

Using N-body numerical simulations, we examine possible mechanisms for the origin of the intracluster starlight features recently discovered in the Coma cluster of galaxies. We show that tidal interactions of a “normal” elliptical galaxy with a symmetrically distributed dark matter potential do not produce the observed intracluster starlight features. A head-on collision of two normal elliptica...