Prague Relativistic Astrophysics

Birgitta Nordstrom

Spiral galaxies are an important part of the visible Universe. In the prototype, our own Milky Way, we can observe the most important component of a spiral galaxy - the disk - in unprecedented detail. In the Solar neighbourhood we can determine the numbers, ages, detailed chemical compositions, and galactic orbits of stars from the entire history of the disk with a completeness and accuracy not available anywhere else in the Universe. Therefore, the solar neighbourhood is a fundamental benchmark for all models of the evolution of galaxy disks.

The Geneva-Copenhagen Survey (Nordström et al. 2004 and Holmberg et al. 2007, 2008) has full spatial, kinematic, metallicity and age information for 14,000 long-lived stars and provides a rich source of data for tests of models of evolution and formation of the Galaxy.

We find that classical evolution paradigm of gradual enrichment and dynamical heating of the Galactic disk seem to fail several of the standard tests related to the stellar metallicity distribution, age-metallicity relation, and age-velocity relation. Both dynamical and kinematic evolution need to be taken into account in sufficient detail by the models to match the best data. A search for signatures of past accretion events in the Milky Way (Helmi et al. 2006) has yielded evidence of ancient substructure in the Galactic Disk and a project to study possible chemical signatures is ongoing.