Aims. The statistical properties of radio halos can be used to discriminate among the possible models for their origin. Therefore an unbiased and exhaustive investigation in this direction is crucial. Methods. With this goal in mind in this paper we revise the occurrence of radio halos in the redshift range 0-0.4, combining the low redshift (z < 0.2) statistical study of XBACs clusters with the...

N-body simulations that follow only a collisionless dark matter component have failed to produce galaxy halos or substructure within dense environments. We investigate the `over-merging' problem analytically and with numerical simulations, by calculating dissolution timescales of halos due to physical and arti cial dynamical e ects. The numerical resolution that has recently been attained is su...

We use the rotation curves of a sample of dark matter dominated dwarf and low-surface brightness (LSB) late-type galaxies to study their radial mass distributions. We find that the shape of the rotation curves is remarkably similar for all (both dwarf and LSB) galaxies in the sample, suggesting a self-similar density distribution of their dark matter (DM) halos. This shape can be reproduced wel...

We investigate effects of time evolution of a rich cluster of galaxies on its member galactic halos in the standard cold dark matter (SCDM) universe using high resolution N-body simulations. We identify several hundred galactic halos within virial radius of our simulated cluster. We also find that a large number of halos have been tidally disrupted at z = 0. Therefore we improve a method of der...

We compute the properties of dark matter halos with mass 10 − 10M⊙ at redshift z = 6 − 11 in the standard cold dark matter cosmological model, utilizing a very high resolution N-body simulation. We find that dark matter halos in these mass and redshift ranges are significantly biased over matter with a bias factor in the range 2− 6. The dark matter halo mass function displays a slope of 2.05±0....

We study how massive halos respond to perturbations. Through numerical solution of the coupled linearized Boltzmann-Poisson equations, we find that halos can transmit and amplify disturbances over large distances within galaxies. In particular, as Weinberg has noted, the halo provides an excellent medium for transmitting disturbances from the outer regions of galaxies to the inner regions. The ...

Periportal halos are an uncommon finding on computerised tomography (CT) of the liver. Here, reported a case of periportal halos and hepatomegaly in a patient with eosinophilic gastroenteritis. A 49-year-old male presented with a six week history of right lower quadrant pain and diarrhoea. A CT of the abdomen showed hepatomegaly and multiple hypodense periportal halos around the patent portal v...

We examine the constraints on theories of galaxy formation that are obtained from observations of damped Lyα (DL) systems, assuming they are gaseous protodisks in dark matter halos. Using the Press-Schechter formalism, we find that the mixed dark matter model, with ΩHDM = 0.3, ΩCDM = 0.65, Ωb = 0.05, and h = 0.5, is ruled out because the number of galactic halos at z ≃ 3 is too small to account...

We calculate the probability to form giant radio halos (∼1 Mpc size) as a function of the mass of the host clusters by using a Statistical Magneto-Turbulent Model (Cassano & Brunetti, these proceedings). We show that the expectations of this model are in good agreement with the observations for viable values of the parameters. In particular, the abrupt increase of the probability to find radio ...

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...