On the core-halo distribution of dark matter in galaxies

We investigate the distribution of dark matter in galaxies by solving the equations of equilibrium of a self-gravitating system of massive fermions (`inos') at selected temperatures and degeneracy parameters within general relativity. Our most general solutions show, as a function of the radius, a segregation of three physical regimes: 1) an inner core of almost constant density governed by degenerate quantum statistics; 2) an intermediate region with a sharply decreasing density distribution followed by an extended plateau, implying quantum corrections; 3) an asymptotic, $\rho\propto r^{-2}$ classical Boltzmann regime fulfilling, as an eigenvalue problem, a fixed value of the flat rotation curves. This eigenvalue problem determines, for each value of the central degeneracy parameter, the mass of the ino as well as the radius and mass of the inner quantum core. Consequences of this alternative approach to the central and halo regions of galaxies, ranging from dwarf to big spirals, for SgrA*, as well as for the existing estimates of the ino mass, are outlined.Comment: 8 pages, 5 figures. Accepted for publication by MNRA

Novel constraints on fermionic dark matter from galactic observables I: The Milky Way

We have recently introduced a new model for the distribution of dark matter (DM) in galaxies based on a self-gravitating system of massive fermions at finite temperatures, the Ruffini-Arg\"uelles-Rueda (RAR) model. We show that this model, for fermion masses in the keV range, explains the DM halo of the Galaxy and predicts the existence of a denser quantum core at the center. We demonstrate here that the introduction of a cutoff in the fermion phase-space distribution, necessary to account for the finite Galaxy size, defines a new solution with a central core which represents an alternative to the black hole (BH) scenario for SgrA*. For a fermion mass in the range $mc^2 = 48$ -- $345$~keV, the DM halo distribution is in agreement with the Milky Way rotation curve data, while harbors a dense quantum core of about $4\times10^6 M_\odot$ within the S2-star pericenter.Comment: 11 pages, 5 figures. Published in Physics of the Dark Univers

The role of self-interacting right-handed neutrinos in galactic structure

It has been shown previously that the DM in galactic halos can be explained by a self-gravitating system of massive keV fermions (`inos') in thermodynamic equilibrium, and predicted the existence of a denser quantum core of inos towards the center of galaxies. In this article we show that the inclusion of self-interactions among the inos, modeled within a relativistic mean-field-theory approach, allows the quantum core to become massive and compact enough to explain the dynamics of the S-cluster stars closest to the Milky Way's galactic center. The application of this model to other galaxies such as large elliptical harboring massive central dark objects of $\sim 10^9 M_\odot$ is also investigated. We identify these interacting inos with sterile right-handed neutrinos pertaining to minimal extensions of the Standard Model, and calculate the corresponding total cross-section $\sigma$ within an electroweak-like formalism to be compared with other observationally inferred cross-section estimates. The coincidence of an ino mass range of few tens of keV derived here only from the galactic structure, with the range obtained independently from other astrophysical and cosmological constraints, points towards an important role of the right-handed neutrinos in the cosmic structure.Comment: 33 pages, 9 figures, version to appear in JCA

Strong lensing by fermionic dark matter in galaxies

It has been shown that a self-gravitating system of massive keV fermions in thermodynamic equilibrium correctly describes the dark matter (DM) distribution in galactic halos and predicts a denser quantum core towards the center of the configuration. Such a quantum core, for a fermion mass in the range of $50$ keV $\lesssim m c^2 \lesssim 345$ keV, can be an alternative interpretation of the central compact object in Sgr A*. We present in this work the gravitational lensing properties of this novel DM model in Milky Way-like spiral galaxies. We describe the lensing effects of the pure DM component both on halo scales, where we compare them to the effects of the Navarro-Frenk-White and the Non-Singular Isothermal Sphere DM models, and near the galaxy center, where we compare them with the effects of a Schwarzschild BH. For the particle mass leading to the most compact DM core, $m c^2\approx 10^{2}$ keV, we draw the following conclusions. At distances $r\gtrsim 20$ pc from the center of the lens the effect of the central object on the lensing properties is negligible. However, we show that measurements of the deflection angle produced by the DM distribution in the outer region at a few kpc, together with rotation curve data, could help to discriminate between different DM models. We show that at distances $\sim 10^{-4}$ pc strong lensing effects, such as multiple images and Einstein rings, may occur. Large differences in the deflection angle produced by a DM central core and a central BH appear at distances $r\lesssim 10^{-6}$ pc; in this regime the weak-field formalism is no longer applicable and the exact general-relativistic formula has to be used. We find that quantum DM cores do not show a photon sphere what implies that they do not cast a shadow. Similar conclusions apply to the other DM distributions for other fermion masses in the above specified range and for other galaxy types.Comment: 10 pages, 8 figures. v2: Version published in PR