Euclid project in Helsinki

ESA Cosmic Vision 2015-2025

Euclid is one of the four space missions of the European Science Agency (ESA) science program for 2015-2025 (Cosmic Vision 2015-2025). The full Cosmic Vision program is: M refers to a "medium-sized" mission and L to a "large" (in cost) mission.

The Dark Energy Problem

The main objective of the Euclid mission is to address the "Dark Energy Problem" - why is the expansion of the universe accelerating? The acceleration was discovered in 1998 by observing distant supernovae. For this discovery, the 2011 Physics Nobel Prize was awarded to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess. According to General Relativity (at least in the homogenous and isotropic approximation to the universe) accelerated expansion requires that the energy density of the universe is dominated by a previosly unknown energy component with negative pressure, "Dark Energy". Another possibility is that General Relativity needs to be modified at cosmological distance scales. A yet third possibility is that inhomogeneities in the universe affect the observations or the expansion of the universe much more than expected. Euclid will address this question by measuring the expansion history of the universe by two complementary probes: If the two methods agree, we can solve from the expansion history the equation of state for the dark energy: how its pressure depends on its energy density. If the two methods disagree, we have discovered that gravity at cosmological scales deviates from General Relativity, and we can compare the observations to the various suggested modified gravity theories.

Euclid - the next cosmology mission

Euclid is a 1.2 meter space telescope with a large field of view, 0.5 square degrees. It carries two instruments: In six years, Euclid will make images of almost half the sky (the part that is 30 degrees or more from the plane of the Milky Way). The exposure time for each 0.5 square degree image is about 1 hour, reaching a sensitivity corresponding to limiting magnitude 24.5. This way we will obtain images of about 1.5 billion galaxies, from which we determine their distortion due to gravitational lensing. For the brighter ones, over 50 million galaxies, NISP will deliver accurate spectroscopic redshifts. These accurate redshifts are used to determine the three-dimensional distribution of galaxies, from which we get the BAO scale at different redshifts. For the rest of the 1.5 billion galaxies we obtain (less accurate) photometric redshifts, from observations at three different infarend bands with NISP, supplemented by observations at different visible bands from ground-based surveys. These redshifts are needed for solving the 3-dimensional distribution of dark matter from the lensing distortions.

Euclid will be launched to an orbit around the second Lagrange point (L2) of the Sun-Earth system. The launch is planned for the last quarter of 2019.

Euclid consortium

There are currently 16 countries in the Euclid consortium: France, Italy, Britain, Germany, Spain, Netherlands, Switzerland, Norway, Austria, Denmark, Finland, Romania, Portugal, Bekgium, USA, and Canada, and about 1400 individual consortium members. Finland joined in 2011. From Finland, there are @4 consortium members, from the Universities of Helsinki, Turku, and Jyväskylä, and Aalto University. The Physics Department of the University of Helsinki has the leading role in Finland.

Euclid at the Department of Physics

The Euclid Consortium members from the Department of Physics, University of Helsinki:

Links

ESA Euclid page
Euclid Consortium Home Page