CORRUGATIONS AND STAR FORMATION ACTIVITY - THE CARINA-SAGITTARIUS ARM

The vertical structure of the Carina-Sagittarius spiral arm is analyzed in relation to the two-dimensional density distribution of young star-gas supercomplexes in the Galactic plane. The Z profile is obtained as a cut of our three-dimensional topography of the Galactic disk in the solar neighborhood (Alfaro, Cabrera-Cano, & Delgado 1991) along the spiral arm segment contained in it. Spectral analysis of this vertical profile leads to a set of significant frequencies, which can best be interpreted in terms of a nonlinear oscillatory process with a characteristic wavelength of 2.4 kpc. The (X, Y) density distribution of young open clusters (YOCs) is computed by using Kernel density estimation methods (Silverman 1986) from the same cluster sample used to obtain the topographic description. A neat correlation between YOC density and displacement from the formal Galactic plane is found when this density distribution is compared with the vertical structure. A new picture of the corrugation structure in spiral arms emerges from the comparison between the vertical and horizontal structures underlying the distributions of young star-gas supercomplexes. In particular, we suggest that the corrugation phenomenon is caused by three-dimensional nonlinear density waves, leading to the three-dimensional distribution of fertile H I matter, where star formation processes are later able to develop and propagate.