ESA-ESO WG report on Fundamental Cosmology (September 2006)

In September 2003, the executives of ESO and ESA agreed to establish a number of working groups to explore possible synergies between these two major European astronomical institutions on key scientific issues. The first two working group reports (on Extrasolar Planets and the Herschel--ALMA Synergies) were released in 2005 and 2006, and this third report covers the area of Fundamental Cosmology.

The Working Group's mandate was to concentrate on fundamental issues in cosmology, as exemplified by the following questions:

• What are the essential questions in fundamental cosmology?
• Which of these questions can be tackled, perhaps exclusively, with astronomical techniques?
• What are the appropriate methods with which these key questions can be answered?
• Which of these methods appear promising for realization within Europe, or with strong European participation, over the next ~15 years?
• Which of these methods has a broad range of applications and a high degree of versatility even outside the field of fundamental cosmology?

From the critical point of view of synergy between ESA and ESO, one major resulting recommendation concerns the provision of new generations of imaging survey, where the image quality and near-IR sensitivity that can be attained only in space are naturally matched by ground-based imaging and spectroscopy to yield massive datasets with well-understood photometric redshifts (photo-z's). Such information is essential for a range of new cosmological tests using gravitational lensing, large-scale structure, clusters of galaxies, and supernovae. All these methods can in principle deliver high accuracy, but a multiplicity of approaches is essential in order that potential systematics can be diagnosed – or the possible need for new physics revealed. Great scope in future cosmology also exists for ELT studies of the intergalactic medium and space-based studies of the CMB and gravitational waves; here the synergy is less direct, but these areas will remain of the highest mutual interest to the agencies. All these recommended facilities will produce vast datasets of general applicability, which will have a tremendous impact on broad areas of astronomy.

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