How cold is Dark Matter? Constraints from Milky Way Satellites

We test the luminosity function of Milky Way satellites as a constraint for the nature of Dark Matter particles. We perform dissipationless high-resolution N-body simulations of the evolution of Galaxy-sized halo in the standard Cold Dark Matter (CDM) model and in four Warm Dark Matter (WDM) scenarios, with a different choice for the WDM particle mass (m_w). We then combine the results of the numerical simulations with semi-analytic models for galaxy formation, to infer the properties of the satellite population. Quite surprisingly we find that even WDM models with relatively low m_w values (2-5 keV) are able to reproduce the observed abundance of ultra faint (Mv<-9) dwarf galaxies, as well as the observed relation between Luminosity and mass within 300 pc. Our results suggest a lower limit of 1 keV for thermal warm dark matter, in broad agreement with previous results from other astrophysical observations like Lyman-alpha forest and gravitational lensing.Comment: 6 pages, 5 figures. Introduction improved, references added. Accepted for publication on MNRAS Letter

Strong gravitational lensing and dynamical dark energy

We study the strong gravitational lensing properties of galaxy clusters obtained from N-body simulations with different kinds of dark energy (DE). We consider both dynamical DE, due to a scalar field self-interacting through Ratra—Peebles (RP) or supergravity (SUGRA) potentials, and DE with constant negative w=p/ρ=−1 (ΛCDM). We have 12 high-resolution lensing systems for each cosmological model with mass greater than 5.0 × 1014 h−1 M⊙. Using a ray shooting technique, we make a detailed analysis of the lensing properties of these clusters, paying particular attention to the number of arcs and their properties (magnification, length and width). We find that the number of giant arcs produced by galaxy clusters changes in a considerable way from ΛCDM models to dynamical dark energy models with an RP or SUGRA potential. These differences originate from the different epochs of cluster formation and from the non-linearity of the strong lensing effect. We suggest that strong lensing is one of the best tools to discriminate among different kinds of dark energ