ATNF Marsfield Lecture Theatre

Tobias Westmeier

The relics of galaxy formation: High-velocity clouds around the Milky Way and other galaxies - Tobias Westmeier Colloquium

More than 40 years after their discovery, the origin of high-velocity clouds (HVCs) and their role in the formation and evolution of galaxies have not yet been fully understood. A major problem is the unkown spatial distribution of most HVCs around the Milky Way. The recent discovery of an HVC population around the other large spiral galaxy in the Local Group, the Andromeda Galaxy (M31), allowed us for the very first time to directly determine the radial distribution and the HI mass function of HVCs. Our results suggest that several of the HVCs found near M31 are likely to be debris left over from the tidal disruption of satellite galaxies. Other HVCs appear spatially isolated and are promising candidates for primordial dark-matter satellites predicted by CDM structure formation simulations.

In my talk I will review the latest results of our HVC studies in the Local Group and the nearby Sculptor Group based on direct HI imaging with single-dish and synthesis telescopes as well as optical absorption spectroscopy of suitable background sources. I will discuss the implications of our results for the nature and origin of HVCs and point out observational strategies to test the concept of HVCs being relics of structure formation.