Andrea Ferrara

The Role of Feedback and Dark Matter on the Evolution of Dwarf Galaxies

There have been a few attempts to combine chemical and dynamical evolution models for dwarf galaxies of various types. We aim to approach the problem in a new, straightforward manner. Our approach follows naturally from the evidence that supernova explosions (SNe) and superbubbles (SB) are the main contributors to the galaxy energy budget, and are easily able to regulate the its metal content. Metals are injected into the ISM during every SN explosion event, and the gas is accelerated in the form of a wind, which may escape from the gravitational well of the galaxy, depending on its dark matter content. The amount of mass and metals lost in an outflow is regulated by the pressure in the ISM, which in turn depends upon the amount of energy injected by previous SNe. If the pressure is initially low an outflow will be strongly favoured, and as subsequent SNe continue to pump energy into the ISM the mass loss will eventually stop in time. This is the result of the fact that random motions induced by SNe generate a non-thermal (turbulent) pressure in addition to the thermal one, and these increasing pressures result in lower outflow velocities and larger mass loss for subsequent SNe. Ultimately, the pressure can be increased to the point that the bubbles produced by SNe are confined in the main body of the galaxy, thus inhibiting the outflow. The competing process is represented by the fact that the parcels of gas (clouds) move and collide at larger and larger velocities, almost always supersonic with respect to their internal sound speed. Radiative dissipation in the shocks following collisions thus stabilizes the system. On this basis, we predict the correlations between overall properties of the galaxy like metallicity, dark matter content, gas mass and velocity dispersion.