Narrow Results

In a previous paper, we determined the statistical distributions for various classes of QSO absorption systems in the framework of the CDM model of the universe with a mass distribution of dark matter halos as given by the Press Schechter mechanism. These were shown to be consistent with the observed distributions for reasonable choices of model parameters. In this paper, we generate Voigt profiles of C IV lines associated with Damped Lyman Alpha systems in the framework of this model, taking into account rotation of disks and random motion of clouds embedded in galactic halos. We compare these with the profiles for a sample of 32 Damped Lyman Alpha systems collected from the literature by performing several statistical tests. These tests compare the width and the degree of asymmetry in the line profiles produced by the rotation of randomly inclined disks and the random velocity of clouds in the galactic halos, with the corresponding quantities in the observed profiles. We find that the kinematic properties predicted by the model are in good agreement with observations provided the disk thickness is about ten thousand times smaller than its radius, which indicates that the material in the disks is concentrated in dense clouds with roughly unit covering factor.

We investigate the structure of halos in the sDGP (self-accelerating branch of the Dvali–Gavadadze–Porrati braneworld gravity) model and the Galileon modified gravity model on the basis of the static and spherically symmetric solutions of the collisionless Boltzmann equation, which reduce to the singular isothermal sphere model and the King model in the limit of Newtonian gravity. The common feature of these halos is that the density of a halo in the outer region is larger (smaller) in the sDGP (Galileon) model, respectively, in comparison with Newtonian gravity. This comes from the suppression (enhancement) of the effective gravity at large distance in the sDGP (Galileon) model, respectively. However, the difference between these modified gravity models and Newtonian gravity only appears outside the halo due to the Vainshtein mechanism, which makes it difficult to distinguish between them. We also discuss the case in which the halo density profile is fixed independently of the gravity model for comparison between our results and previous work.

We analyze the intriguing possibility of explaining both dark mass components in a galaxy: the dark matter (DM) halo and the supermassive dark compact object lying at the center, by a unified approach in terms of a quasi-relaxed system of massive, neutral fermions in general relativity. The solutions to the mass distribution of such a model that fulfill realistic halo boundary conditions inferred from observations, develop a high-density core supported by the fermion degeneracy pressure able to mimic massive black holes at the center of galaxies. Remarkably, these dense core-diluted halo configurations can explain the dynamics of the closest stars around Milky Way’s center (SgrA*) all the way to the halo rotation curve, without spoiling the baryonic bulge-disk components, for a narrow particle mass range $m{c}^2\sim 10$–$10^2$keV.