  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 1-D and 3-D tests are shown. The paper is mainly
dedicated to the presentation of the code and to the critical discussion of its
performances. In particular great attention is devoted 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 latter in form of gas and stars, cooling, thermal
conduction, star formation, and feed-back from Type I and II supernovae,
stellar winds, and ultraviolet 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
and chemical evolution of a disk-like galaxy with and without feed-back. 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
spectro-photometric code from which the integrated spectra, magnitudes, and
colors (together with their spatial gradients) can be derived.
