Absorption and emission line studies of gas in the Milky Way halo

TL;DR

This study investigates the physical properties and distribution of neutral and ionised gas in the Milky Way halo, combining radio and optical data to understand gas accretion and galaxy evolution.

Contribution

It provides a comprehensive analysis of low-column density gas structures in the MW halo using combined HI 21-cm and quasar absorption line data.

Findings

Identification of low-column density gaseous structures with substantial area filling factor.

Analysis of the relation between MW halo gas and quasar absorption systems.

Insights into the distribution and physical parameters of halo gas at densities below 10^19 1/cm^2.

Abstract

We perform a systematic study of physical properties and distribution of neutral and ionised gas in the halo of the Milky Way (MW). Beside the large neutral intermediate- and high-velocity cloud (IVC, HVC) complexes there exists a population of partly ionised gaseous structures with low-column densities that have a substantial area filling factor. The origin and nature of these structures are still under debate. We analyse the physical parameters of the MW halo gas and the relation to quasar (QSO) metal-absorption line systems at low and high redshifts. For this purpose we combine new HI 21-cm data from the EBHIS and GASS surveys with optical quasar absorption line data to study the filling factor and distribution of these gaseous clouds in the halo at HI densities below 10^19 1/cm^2. This study is important to understand the evolution of the MW in particular and the gas accretion mechanisms of galaxies in general.