Infall of Gas in Galaxies and Triggered Star Formation

Abstract

While the importance of merging, accretion, and infall processes in determining galactic evolution is well established both theoretically and observationally, details on how such processes are taking place nowadays even in our own Galaxy are still relatively poorly known, especially due to large remaining uncertainties on the location and origin of high velocity clouds. In this paper we focus on the possible role that galactic outflows and gas infall may have on directly triggering star formation in the halo and in galactic disks. While compelling evidence has been accumulating in recent years suggesting that some level of star formation directly triggered by outflows is very likely to exist in the halo of some galaxies, the evidence for star formation dynamically triggered by infall is far more elusive due to confusion with other, more efficient large-scale star forming mechanisms operating in the galactic disk. Despite of increasingly realistic simulations of the gas circulation between the gas and the halo and of high velocity cloud impacts on galactic disks, the efficiency of star formation directly triggered by such impacts remains an open question.