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A complete view of the Universe out to high redshifts

Final Activity Report Summary - DANVER2004 (A complete view of the Universe out to high redshifts)

Galaxies are the principal building blocks of our Universe. They are typically classified in elliptical, spiral and irregular galaxies with many subclasses, depending on their morphology. Many aspects of galaxy formation like progenitors, timescales and exact processes are still not understood. In particular, possible links between the various galaxy types have been proposed but are not yet satisfactorily verified. As the timescales involved are of the order of several 10^9 years, it is obvious that galaxy formation and evolution studies can only be made with the help of large and deep surveys which span over a large range of the age of the Universe.

The present study yields a first quantitive clue to the galaxy formation and evolution when the Universe had 30 % of the present age. It is widely accepted that most of the stellar mass in the local Universe is contained in old, massive, red spheroids (elliptical galaxies) residing in high-density cluster environments, while most of the star formation is occurring in smaller-mass, disk-dominated blue objects (spiral galaxies) populating the lower density environments. Is that still valid in the early Universe? There must have been a time when this was reverse with the densest regions in the Universe most actively forming stars.

The primary goal of the performed project was to get deep insight in our understanding of these evolutionary properties extending our knowledge to an age close to the Big Bang.

The main result obtained supports the scenario where star-formation activity proceeds from high- to low-mass systems, with massive galaxies having formed most of their stars at an early epoch, while low-mass systems have been forming their stellar component continuously till the present epoch. In this research, a clear link was established between younger (older) stellar populations and low- (high-) mass galaxies at high redshifts, confirming and extending at later epochs the results obtained in similar studies in the local Universe.