GALAXY FORMATION AND EVOLUTION - I - THE PADUA TREE-SPH CODE (PD-SPH)

In this paper we report on PD-SPH, the new TREE-SPH code developed in Padua. The main features of the code are described and the results of a new and independent series of 1D and 3D tests are shown. The paper i s mainly dedicated to the presentation of the code and to the critical discussion of its performance. In particular, great attention is devo ted to the convergency analysis. The code is highly adaptive in space and time by means of individual smoothing lengths and individual time- steps. At present it contains both dark and baryonic matter, this latt er in the form of gas and stars, cooling, thermal conduction, star for mation, feedback from Type I and II supernovae, stellar winds, and ult raviolet flux from massive stars, and finally chemical enrichment. New cooling rates that depend on the metal abundance of the interstellar medium are employed, and the differences with respect to the standard ones are outlined. Finally, we show the simulation of the dynamical an d chemical evolution of a disc-like galaxy with and without feedback. The code is suitably designed to study in a global fashion the problem of formation and evolution of elliptical galaxies, and in particular to feed a spectrophotometric code from which the integrated spectra, m agnitudes and colours (together with their spatial gradients) can be d erived.