On the origin of gaseous galaxy halos - Low-column density gas in the Milky Way halo

TL;DR

This paper investigates the origin and properties of gaseous halos around galaxies, using the Milky Way as a case study to understand the physical conditions and distribution of halo gas in galaxy formation.

Contribution

It provides detailed analysis of neutral and ionised gas in the Milky Way halo, revealing similarities with halos around other disk galaxies across cosmic time.

Findings

Gas in the Milky Way halo has similar column-density distribution to other disk galaxies.

Physical properties of halo gas are consistent across different galaxy environments.

Halo gas plays a key role in galaxy formation and evolution processes.

Abstract

Recent observations show that spiral galaxies are surrounded by extended gaseous halos as predicted by the hierarchical structure formation scenario. The origin and nature of extraplanar gas is often unclear since the halo is continuously fueled by different circulation processes as part of the on-going formation and evolution of galaxies (e.g., outflows, galaxy merging, and gas accretion from the intergalactic medium). We use the Milky Way as a laboratory to study neutral and mildly ionised gas located in the inner and outer halo. Using spectral line absorption and emission measurements in different wavelength regimes we obtain detailed information on the physical conditions and the distribution of the gas. Such studies are crucial for our understanding of the complex interplay between galaxies and their gaseous environment as part of the formation and evolution of galaxies. Our analysis suggests that the column-density distribution and physical properties of gas in the Milky Way halo are very similar to that around other disk galaxies at low and high redshifts.