2008ApJ...685L.125D

The Galaxy harbors a population of high Galactic altitude clouds (HGACs) which are, in some cases, similar to those in the disk. About 3% of open clusters younger than 100 Myr are located at least 200 pc away from the disk; in the outer Galaxy, some embedded clusters are found at 500 pc. But, by what mechanism could star clusters form far from the regions in which the usual driving forces of triggered star formation can act efficiently? In this Letter we investigate whether passing preexisting star clusters can induce tidal forces able to trigger star formation in HGACs. The interaction is studied using the impulse approximation and results are compared with available evidence. Our analytical estimate indicates that this mechanism is able to induce star formation if passing clusters are massive enough, i.e., globular clusters. The expected number of interactions appears to be consistent with the observed star formation rate at high Galactic altitude.