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IAU General Assembly XXVII - Joint Discussion #12

August 10 - 11, 11:00 - 17:30h, both days.

Recent observational and theoretical results show that the period between recombination and the end of the reionization era is very dynamic in terms of star and galaxy formation. At z~6 we find galaxies already in place, with stellar masses rivaling those of giant local systems. The age of the stars in these high redshift galaxies is several hundred million years, putting their formation epoch at z~9-15, well into the reionization period. Yet, these stars exhibit characteristics similar to those found in lower redshift galaxies. Furthermore, QSOs at z~6 imply an extremely efficient fueling mechanism during the first few hundred million years after the recombination epoch. These new observations are raising questions about where the first generations of stars were formed, how the first galaxies were assembled, can their low redshift counterparts be identified and what role did the early galaxies play in the reionization process?

These recent results have become available through multiwavelength observations, extending from the observed UV to infrared wavelengths. Large datasets, combining both ground- and space-based telescopes, and covering sufficiently large areas to counteract cosmic variance, have only recently become available and are expected to reach their full potential by the time of the proposed Joint Discussion. Until the launch of the JWST, essentially all the observational information of these very high redshift galaxies will continue to consist of broad-band photometric data. These are interpreted in terms of stellar synthesis models. The results are therefore strongly dependent on the accuracy of the stellar synthesis models. Recently there have been important advances in our understanding of the contribution to the global spectral energy distribution of galaxies from late-stage stellar evolution. It is now possible to critically review the observational data and its interpretation in view of these new developments.

The formation of galaxies through hierarchical merging is a fundamental paradigm in LCDM models. While the theory can successfully account for and model the evolution of dark matter halos, inclusion of the star formation process still presents a problem. There are indications that early star formation plays a significant, perhaps major, role in the reionization process. Hence, a better understanding of how the first stars form and interact with their environment is fundamental to understand the reionization process. Combining the new observational data with models can potentially shed some light on these issues. This Joint Discussion brought together observers and theorists for a discussion of where we stand today and what progress can be made in the near future with improved models and new observational facilities such as ALMA, JWST and others.

Scientific Topics:

- Population III stars
- Emergence of the first normal stellar populations
- Formation of the first galaxies
- Formation of the first AGNs
- Co-evolution of stars and AGNs
- Massive galaxies in the reionization epoch
- Sources of reionization
- Metallicities and dust in the first Gyr
- Implications on results from revised stellar synthesis models
- Observational challenges

Supporting Division and Commissions:

Division VIII        - Galaxies and the Universe

Commission 28    - Galaxies
Commission 47    - Cosmology

Important Note:

Joint Discussion 12 was part of the scientific programme of the XXVII General Assembly of the International Astronomical Union, which took place in Rio de Janeiro, Brazil, August 3-14 2009. This website contains information directly relevant to the Joint Discussion #12: The First Galaxies: Theoretical Predictions and Observational Clues.