HI shells in the Leiden/Argentina/Bonn HI survey

TL;DR

This study systematically identifies and analyzes 333 HI shells across the Milky Way using the Leiden/Argentina/Bonn survey, revealing their size distribution, spatial density, and porosity.

Contribution

It introduces a new method for identifying HI shells and provides the first comprehensive catalog with statistical properties of shells in the Galaxy.

Findings

Size distribution follows a power law with index 1.8.

Surface density of large shells in the solar neighborhood is about 4 per kpc^2.

2D porosity of HI shells is approximately 0.7.

Abstract

We analyse the all-sky Leiden/Argentina/Bonn HI survey, where we identify shells belonging to the Milky Way. We used an identification method based on the search of continuous regions of a low brightness temperature that are compatible with given properties of HI shells. We found 333 shells in the whole Galaxy. The size distribution of shells in the outer Galaxy is fitted by a power law with the coefficient of 2.6 corresponding to the index 1.8 in the distribution of energy sources. Their surface density decreases exponentially with a scale length of 2.8 kpc. The surface density of shells with radii >= 100 pc in the solar neighbourhood is around 4 per kpc^2 and the 2D porosity is approximately 0.7.