Topography of the galactic disk: Z-structure and large-scale star formation

A sample of young open clusters (age less than 107 yr) with cataloged distances, treated with the Kriging techniques have been used to delineate a three-dimensional morphological description of the Galactic disk defined by the young stellar population. The basic idea entails considering the values of the positional variable Z for the cluster sample as prospectings of the displacement of the Galactic disk in respect to the Galactic equator in the (X, Y) plane. The Kriging technique is described with special emphasis on its application to the automatic cartography problem. A view of the Galactic disk in a region of about 3 kpc around the Sun emerges from this treatment, showing a trough-peak structure with four main depressions as the more striking features. The most prominent depression, named Big Dent, is apparent at ≈1.8 kpc in the l ≈ 240° direction. This feature has an elliptical shape with axis sizes of 1.5 and 3 kpc, reaching a Z value of 200 pc below the formal Galactic plane. Two-dimensional sections across some selected directions of our topography show profiles in good agreement with previous observational studies, based on different object samples. The four depressions are found to be related to the four young star-gas supercomplexes detected in the solar vicinity by Efremov & Sitnik. This finding leads us to suggest a physical link between the processes driving the large-scale star formation in our Galaxy and those being able to generate the Z-structure of the Galactic disk described in this work. The disk-high-velocity cloud collisions are considered, in this context, the most plausible dynamical mechanism, that has led to the present disk structure.