CCACAO · COSMOLOGY AND COMPUTATIONAL ASTROPHYSICS AT CATANIA ASTROPHYSICAL OBSERVATORY

Final Activity Report Summary - TBC (Cosmology and Computational Astrophysics at Catania Astrophysical Observatory)

The COSMOCT Project aimed at enabling the creation of a Cosmology and Computational Astrophysics group within the Catania Astrophysical Observatory, which since now is part of INAF, the National Institute for Astrophysics. Since the beginning, the strategy adopted was that of a deep synergy between Extragalactic Astrophysics, Cosmology and Computational and Visualisation Techniques: the emphasis was given to two targets: 1) Writing numerical codes which would have enabled to perform REALISTIC simulations of some selected cosmological targets, or which could optimise existing numerical tools, like software packages for the analysis of images of the sky; 2) Developing analysis and visualization tools explicitly targeted at the need of the astrophysical community, particularly of the theoretical astrophysicists and those having to deal with large catalogues of galaxies and Active Galactic Nuclei. The realm of today's Extragalactic Astrophysics is very large. Observations from ground and from space have enabled astrophysicists to observe galaxies very near the epoch when the entire Universe was born: the farthest galaxies we see today seem to be already in place at an epoch representing only about 6% of the age of the Universe. When the COSMOCT project started, on August 1st, 2004, there were only a handful of galaxies having an age corresponding to 20% of the age of the Universe: now we have statistical samples of these objects, and we are then in a position to probe very early epochs in the formation of our Universe. The complexity of the physics of galaxy formation however hinders any attempt at making realistic predictions. The fundamental physical laws determining these processes (atomic cooling mechanisms, gravitational collapse) are well known, but their combination in the modelling of the stellar formation problem results in mathematical equations which, in their generality, are unmanageable. For this reason, numerical simulations represent a unique tool to attempt to understand the evolution of galaxies, and to make predictions which are then compared to observations. A group of young researchers, in addition to the experienced staff members, brought fresh ideas into the project and contributed to attain few interesting results: A) The detection and measurement of the distribution of the elusive Dark Matter in the Universe, through the measurement of the small deformations of the shape of very distant galaxies (the so-called Weak Gravitational Lensing). A software package to measure these tiny deformation with high precision was developed and applied to measure the unseen Dark Matter distribution in a Cluster of galaxies (Abell 209), which showed a complex double structure. B) Direct simulations of the emergence of the "Red Sequence". Elliptical galaxies are mostly regarded as "fossil" system, where star formation ended few billion years ago. But we observe that this process was highly unequal. The simulations performed using our codes have, for the first time, have elucidated the deep correlation between star formation and galaxy assembly, which results into the creation of the so called "Red Sequence". We now know that some more effective agent is needed to inhibit star formation: possibly the feedback from an AGN. C) AGN feedback on host galaxies. - The Black Holes hosted in the central regions of galaxies can emit relativistic jets, which can significantly affect global star formation in the galaxy. This interaction is very fast, compared to cosmic timescales, so simulations are essential to understand this phenomenon. We have performed very realistic simulations of this phenomenon, using the most advanced computational techniques, and we have demonstrated that it can significantly alter galaxy colours. In addition, we have studied different subjects like the stability of galactic disks, alternative cosmological models, the nature of galaxies in very low density environments, and others.

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