fenomenologia galattica dall'interazione tra materia oscura e barioni

There is strong evidence that the mass discrepancy in spiral galaxies anticorrelates with the baryonic acceleration, i.e. it follows a mass discrepancy-acceleration relation ¿MDAR¿. The observed tightness of this relation has been seen as a challenge to current galaxy formation models, while it can be explained by Modified Newtonian Dynamics (MOND). This thesis work analyses a model of dark matter-baryon interaction that can reproduce the MDAR without the need of fine-tuned feedback processes or modification of gravity. The three basic assumptions are: 1) the relaxation time of DM particles is comparable to the dynamical time in disk galaxies; 2) DM exchanges energy with baryons due to elastic collisions; 3) the product between the baryon-DM cross section and the typical energy exchanged in a collision is inversely proportional to the DM number density. Under this assumptions is it possible to write, starting from the collisional boltzmann equation, an heat equation for the DM temperature sourced by energy exchange with baryons. This model predicts a strong scattering cross section of order σ/m ~ 1cm2 /g, therefore to satisfy direct detection constraints our DM particles must be either very light or very heavy. The first part discusses the missing mass problem, dark matter hypothesis and MOND theory. The second chapter is focused on the MDAR and other phenomenological relations as the baryonic Tully-Fisher relation (BTFR), the Faber-Jackson relation and the central surface density relation. Furthermore the diversity of rotation curves problem and the baryon-halo conspiracy are discussed. The third part discusses the article by R.Penco B.Famey J.Khoury ¿Emergence of the mass discrepancy-acceleration relation from dark matter-baryon interactions¿ (1), in which they propose the idea and analyse the case of very heavy DM particles (mDM >>mB), corresponding to cooling of DM by baryons. The Poisson equation, Jeans equation and heat equation for a system of second order differential equations whose solution determines DM density and velocity dispersion profiles. Through an heuristic treatment this system is analytically solved, showing that the model can reproduce the MDAR and the BTFR. In chapter four are shown my numerical results for this cooling case, which confirm that it can account for the MDAR and that the resulting DM density profile is well approximated by a modified Hubble profile as in (1). Then are shown my results for the central surface density relation, the angular momentum-mass relation and the correlation between stellar scale lenght and halo core radius.