HI Shells in the Leiden-Dwingeloo HI Survey

Abstract

An algorithm of an automatic search for HI shells is presented and results of identifications in the Leiden-Dwingeloo HI survey are shown. An identification algorithm searches for local minima in channel maps, then creates 3-dimensional objects, HI holes. There is no a priori constraint on the shape of an HI hole, only the dimension criterion: dimensions of the structure must lie in a preselected interval. When this algorithm is applied to the Leiden-Dwingeloo HI survey, it finds about 1000 structures, which are seen in 4 or more consecutive velocity channels (Δv ≥ 4 kms ⁻¹). A total energy contained in all structures in the Milky Way is of the order of 10⁵⁵ erg, which is less than the energy corresponding to the observed SNR. 80% of the energy contained in holes resides at low galactic z-coordinates, |z| < 2 kpc.