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Laboratoire d’Astrophysique de Marseille

IXth Marseille Cosmology Conference

Du 22 au 26 juillet 2013 - Hôtel Aquabella, Aix-en-Provence

Physical Processes of Galaxy Formation : Consensus and Challenges

The last decade has brought us into the so-called precision cosmology era, as observations of the large-scale structure of the universe, the cosmic microwave background and distant supernovae have given us what is widely believed to be an accurate quantitative description of the expansion and the geometry of the universe. The theory of the formation and evolution of galaxies is also becoming a mature subject, although it faces a number of open problems, such as the formation of pure discs, the predicted overabundance of satellite galaxies, and the size evolution of early-type galaxies.
Are these and other observations real challenges for the standard theory of galaxy formation in a cosmological context ? This is a difficult question because the standard theory must account for many uncertain physical ingredients that blur its predictions.
Indeed, the formation of galaxies is the result of the complex interaction of many different physical processes : the gravitational instability of primordial density fluctuations, the dissipative infall of gas to the centres of dark matter haloes, star formation and stellar evolution, stellar feedback, disc instabilities, galaxy interactions, the thermal and chemical evolution of the interstellar and intergalactic medium, the growth of supermassive black holes, and its impact on the surrounding gas.
Semianalytic models provide a unified framework to explore how the interplay between these processes induces different scenarios of galaxy formation, which can be compared with the observations. The power of this method depends critically on the number of observational constraints and on our ability to describe correctly the individual processes included in the models.
While the last decade has witnessed a spectacular increase in both the quality and the quantity of the observational constraints, the physics of many processes, such as those associated with stellar and black hole feedback, are still poorly understood. As a result, our description of these processes depends on assumptions that are often arbitrary. Hydrodynamic simulations follow the dynamics of dark and luminous matter on galactic scales in a way that is much more self-consistent and much less assumption-dependent than that of semi-analytic models, but they are affected by resolution limitations. Therefore the uncertainties about physical processes persist in the form of subgrid physics.

This conference comes at a time when multi-wavelength deep surveys across the electromagnetic spectrum begin to unveil the global evolution of the galaxy and quasar populations up to the epoch of reionization and when spatially resolved spectroscopy studies begin to unveil internal physics and detailed morphologies at z<3. Its purpose is to gather theorists and observers to review the processes that play a role in the formation of galaxies, to assess our understanding of the underlying physics, to establish a level of consensus in the way they should be modeled, and to determine which observations can best discriminate between scenarios and ultimately disentangle the individual processes. Only when we are confident that we have modelled the individual physical processes correctly will we be able to assess whether the current problems are fundamental challenges that require us to rethink the big picture.

Lieu : Hôtel Aquabella
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