21 cm cosmology and dark energy

Abstract : 3D mapping of matter distribution in the universe through the 21 cm radio emission of atomic hydrogen is a complementar y approach to optical sur veys for the study of the Large Scale Structures, in par ticular for measuring the BAO (Bar yon Acous- tic Oscillation) scale up to redshifts z=3 and constrain dark energy. We propose an instrument to carr y such a sur vey through intensity mapping, without detecting individual galax- ies. An R&D effor t (electronics, antenna/feeds, software, . . . ), initiated in 2007, is being carried by an international team (France, USA, Canada, China), to design a multi-beam (100-1000 beams), large field of view (10-100 sq. deg) and large bandwidth (100 MHz) instrument suited for 21 cm intensity mapping at z = 1 (http://bao.lal.in2p3.fr/21cm/).