Scientific Rationale

Understanding galaxy formation is one of the outstanding goals of modern astrophysics and cosmology. The relics of the physical formation mechanisms are left in the galaxy kinematics and stellar populations, but often are difficult to isolate from the main galactic body. Galaxy halos - where the dynamical timescale is comparable to the age of the Universe - offer a unique opportunity to find the fingerprints of the various processes that contributed to galaxy formation, and to constrain the distribution of dark matter at  large radii. Robust observations - out to 2 effective radii and more - and detailed modeling became available only recently. Investigations of outer halos are expected to provide in the near future new constraints on galaxy assembly, stellar population content, and dark matter properties.

The aims of the workshop are:
  1. To constrain the formation process of galaxies and their halos by looking at the signatures in the stellar population and kinematics in combination with state of the art dynamical modelling and high-resolution numerical simulations.
  2. Identify the most efficient observational and theoretical tools and techniques, and surveys to adopt for this purpose.

The talks are expected to cover the following aspects:
  1. What are the observational results regarding the stellar populations and kinematics of massive galaxy halos? What is known about the Local Group, the nearby Universe and higher redshifts?
  2. What are the predictions of galay formation models about the kinematics, and stellar population content and distribution in the halos? Which models are favoured in the light of the new observations at large radii? Did stellar halos form together with the central galaxies or do they have a different origin?  What are the progenitors of the stars in the halo, and when were they accreted onto the galaxy? What is the role of mergers and gas accretion, and that of dwarf galaxies as building blocks of galaxy halos?
  3. Are up-to-date stellar population models (e.g. their spectral resolution, metallicity coverage) adequate to interpret the observations?  What are the driving uncertainties in terms of stellar evolution? What are the most efficient techniques for data analysis, e.g. selected spectral indices, full spectral fitting, or broad-band colours, and their strengths and limitations?
  4. What are the best observational strategies in the light of the existing and forthcoming instruments and surveys? Currently, several observational techniques are adopted, such as integral field units, deep long-slit and multi-slit spectroscopy, globular clusters in the halos, multi-band photometry. The results from these techniques will be compared to understand their advantages and disadvantages in terms of statistics of the number of objects studied, redshift range covered, radial extent and the ability to detect multiple stellar populations.