Galactic fountains and their connection with high and intermediate velocity clouds

Context. Sequential supernova explosions create supershells which can break out a stratified medium producing bipolar outflows. The gas of the supershells can fragment into clouds which eventually fall toward the disk producing the so called galactic fountains. Aims. The aim of this paper is to calculate the expansion law and chemical enrichment of a supershell powered by the energetic feedback of a typical Galactic OB association at various galactocentric radii. We study then the orbits of the fragments created when the supershell breaks out and we compare their kinetic and chemical properties with the available observations of high and intermediate velocity clouds. Methods. We use the Kompaneets (1960) approximation for the evolution of the superbubble driven by sequential supernova explosions and we compute the abundances of oxygen and iron residing in the thin cold supershell. We assume that supershells are fragmented by means of Rayleigh-Taylor instabilities and we follow the orbit of the clouds either ballistically or by means of a hybrid model considering viscous interaction between the clouds and the extra-planar gas. Results. Given the self-similarity of the Kompaneets solutions, clouds are always formed ∼448 pc above the plane. If the initial metallicity is solar, the pollution from dying stars of the OB association has a negligible effect on the chemical composition of the clouds. The maximum height reached by the clouds above the plane seldom exceeds 2 kpc and when averaging over different throwing angles, the landing coordinate differs from the throwing coordinate ∼ 1 kpc at most. Conclusions. The range of heights and [O/Fe] ratios spun by our clouds suggest us that the high velocity clouds cannot have a Galactic origin, whereas intermediate velocity clouds have kinematic properties similar to our modeled clouds but overabundance observed for the [O/Fe] ratios which can be reproduced only with initial metallicities which are too low compared for those of the Galaxy disk.