Orateur
Description
The measurement of the Cosmic Microwave Background spectrum made by COBE/FIRAS in the 1990s showed that the CMB spectral energy distribution is close to a perfect blackbody. However, the CMB spectrum contains tiny departures from a perfect blackbody to $\Delta I/I \simeq 10^{-5}$, referred to as spectral distortions. CMB spectral distortions encode information about the full thermal history of the Universe.
The two main types of CMB spectral distortions are the Compton $y$-distortion from energy release in the optically thin regime at redshifts $z < 5 \times 10^{4}$, and chemical potential or $\mu$-distortion from the optically thick regime imprinted at $z > 5 \times 10^{4}$. CMB spectral distortions allow us to access information, from the present to the very early Universe, that cannot be extracted in any other way.
High-precision spectroscopy of the CMB is one of the three themes that have been selected by the ESA Voyage 2050 programme. Several dedicated space missions such as PIXIE, PRISTINE, and FOSSIL have been proposed since 2011. Additionally, balloon-borne missions, such as BISOU, have also been considered as a pathfinder of a future space mission dedicated to CMB spectral distortions.\
I will present an effort undertaken to define future missions and instruments dedicated to the measurement of the CMB spectral distortions. It combines two models allowing for sensitivity estimates that could be reached by such projects. The first is an versatile photometric model based on key instrument subsystem choices together with their parameters. The second is a sky emission model taking into account spatially varying foregrounds at frequencies relevant to CMB spectral distortions.
Combining outputs of those models, optimizing both instrument concept and mission parameters (mission duration, scanning strategy, ...) can be achieved. This would be apply here in the case of FOSSIL, a space mission propose to answer the recent ESA M7 proposal and BISOU, a CNES Phase 0 study for a balloon-borne mission.
