Nature versus nurture for galaxies
Cosmic structures are believed to form in a bottom-up fashion, with small systems like galaxies and groups of galaxies forming first and later merging into more massive structures like clusters of galaxies. Determining how individual galaxies form and evolve is one of the main unsolved problems of modern astrophysics. The observed properties of galaxies have long been known to depend on the environment in which they are located. The physical origin of the observed environmental trends is, however, still subject to debate. Much of the argument centres on whether these trends are the end product of physical processes that have come into play after the galaxies have become part of groups or clusters (the nurture hypothesis), or whether they are established before the accretion into more massive systems, due to galaxy formation proceeding differently in different environments (the nature hypothesis). Funded by the EU, the STGDELUCIA2007 (Galaxies through the cosmic ages: The role of primordial conditions and environmental effects) project aimed to understand the origin of the observed physical properties of galaxies and their dependence on the environment, as a function of cosmic time. The team has provided characterisations of the limits of current galaxy formation models, using a detailed comparison between observational data and the predictions of each model. This systematic comparison allowed the identification of specific directions for improvements. An enhancement of the treatment of satellite galaxy evolution gives results in better agreement with data, but the main limitations of our current models was found to be their treatment of the 'self-regulation' between star formation and feedback. An analysis of the environmental history of galaxies currently residing in groups and clusters shows that there is a critical environment for galaxy evolution, with total masses ~ 10^13 Msun and typical timescales of the order of 5-7 Gyr for galaxy evolution in dense environments. Further, the first detailed controlled N-body simulations of the evolution of disk galaxies in groups have been completed. These have quantified the relative roles of tidal fields and low-velocity close encounters and reveal that the former plays the dominant role.
Keywords
Galaxies, galaxy formation, STGDELUCIA2007, galaxy evolution, tidal fields
