Abundances in High-Velocity Clouds

Argelander-Institut für Astronomie, Bonn University, Auf dem Hügel 71, 53121 Bonn, Germany

Abstract

In this article I briefly review recent abundance measurements in intermediate- and high-velocity clouds (IVCs and HVCs, respectively) in the halo of the Milky Way. FUSE and STIS absorption line data indicate that these clouds span a metallicity range between ~0.1−1.0 solar, suggesting that they cannot have a single origin. Most likely, the infall of gas from the intergalactic medium and from satellite galaxies is responsible for the population of low-metallicity HVCs like Complex C, while the more metal-rich clouds (in particular the IVCs) represent Galactic material as part of a galactic fountain. The detailed analysis of particularly interesting ions and molecules (e.g., O i, D i, N i, O vi, and H₂) gives a detailed insight into the chemical composition of individual clouds and further provides important information on the physical conditions in these objects.