At large angular scales, the astronomers observe the CMB fluctuations to probe the first seconds of the Universe. But there are also some fluctuations at smaller angular scales due to objects located on the way of the CMB photons. In other words, the CMB also constitutes a print of the structure of the universe along its history. CMB photons which travel through a hot gas area in the galaxy clusters gain energy, transmitted by the hot gas electrons by diffusion. By comparing a reference area with the area where this effect is observed (known as the Sunyaev-Zel?dovich effect, or the SZ effect), the cosmologists can deduce the presence of a galaxy cluster and its mass. In addition, this effect is totally independent of the distance which separates us from the object, so the galaxy clusters contribution will be the same, would it be relatively close or very distant. Thus, the SZ effect detection will allow the cosmologists to observe clusters invisible in the optical or in X-rays range. These galaxy clusters which are the largest gravitationally bound objects in the universe are made of 85% of dark matter, 13 % of hot gas and a few % of galaxies, and they particularly interest the cosmologists. First of all because the census of a great number of these objects located sometimes at very remote distances makes it possible the measurement of a fundamental cosmology parameter which characterizes the velocity of the universe expansion, the Hubble constant. And then because their study could bring some clues to the enigma of the energy which would be at the origin of an acceleration of the universe expansion, the so called dark energy. This energy which counts for 70% of the universe density is opposed to gravity and cosmologists suspect that its action evolved in time. This is the measurement of this time evolution that cosmologist would like to achieve by observing these galaxy clusters. Indeed, these clusters formed very early and continued to gather their mass through time. However, dark energy being opposed to the force exerced by gravity, prevents the formation of very massive galaxy clusters. By carrying out countings of these objects at various epochs of the universe history, and by measuring the proportion of very massive galaxy clusters which have formed at various epochs, cosmologists hope learning more on dark energy.

During the last ten years, the precision and the sensitivity achieved by the instruments have allowed the astronomers to observe an acceleration of the universe expansion, caused by a mysterious energy called dark energy. Its origin and its time evolution are totally unknown although it counts for 74 % in the entire density of the universe.

? D. M?karnia - G. Durand When it comes to us, the CMB contains some prints of astrophysical objects which were on its way. When the CMB photons cross through a galaxy cluster, they gain energy. To observe this Sunyev-Zel?dovich effect, the Italian COCHISE telescope has been set up in 2006 at Dome C. Its main purpose is to achieve a survey of these galaxy clusters in order to know more about the dark energy.

The requisite precision to measure SZ effect does not constitute the main difficulty to surmount. The few tenth of mK to detect to analyze SZ effect are 10 to 100 times higher than the precision now regularly obtained by many instruments dedicated to the CMB, either in space (WMAP) or on the ground, in particular in Antarctica (at the Scott-Amundsen base located at the South pole with the South Pole Telescope, or at the Italian base located at Terra Nova Bay with the Italian Astrophysical Observatory in Antarctica) and 1000 times higher than measurements required for the B-modes evoked previously. The main difficulty lies rather in the discrimination of the SZ effect from other ?foreground? effects caused mainly by the travel of the CMB trough our galaxy, our solar system and our atmosphere as well. These effects can be limited by choosing a site where the atmosphere is particularly stable and which allows uninterrupted observations. Moreover, CMB observations at several wavelengths in the millimeter-wave and submillimeter-wave range, limits possible confusion between the SZ effect detection and a ?foreground? contribution. For these reasons, Dome C seems to be a very good site to observe the SZ effect, not only because of the atmosphere stability and the possibility to achieve uninterrupted observations over several months, but also because the very small quantity of precipitable water vapour in the atmosphere opens submillimeter-wave range to observe the SZ effect at several wavelengths. This is one of the purposes of the COCHISE telescope (Cosmological Observations At Concordia with High-sensitivity Instrument for Source Extraction) which has been installed at Dome C in January 2007 by an Italian team. With a 2.60 meters primary mirror, COCHISE is a telescope entirely dedicated to observations in the millimetre-wave and submillimeter-wave range one of its main program is the accurate observation of the CMB to detect SZ effect in order to know more about the dark energy.