Foregrounds and CMB Experiments: I. Semi-analytical estimates of contamination

As Cosmic Microwave Background (CMB) measurements are becoming more ambitious, the issue of foreground contamination is becoming more pressing. This is especially true at the level of sensitivity, angular resolution and for the sky coverage of the planned space experiments MAP and PLANCK. We present in this paper an indicator of the accuracy of the separation of the CMB anisotropies from those induced by foregrounds. Of course, the outcome will depend on the spectral and spatial characteristics of the sources of anisotropies. We thus start by summarising present knowledge on the spectral and spatial properties of Galactic foregrounds, point sources, and clusters of galaxies. This information comes in support of a modelling of the microwave sky including the relevant components. The accuracy indicator we introduce is based on a generalisation of the Wiener filtering method to multi-frequency, multi-resolution data. While the development and use of this indicator was prompted by the preparation of the scientific case for the \plancks satellite, it has broader application since it allows assessing the effective capabilities of an instrumental set-up once foregrounds are fully accounted for, with a view to enabling comparisons between different experimental arrangements. The real sky might well be different from the one assumed here, and the analysis method might not be in the end Wiener filtering, but this work still allow meaningful {\em comparative} studies. As a matter of examples, we compare the CMB reconstruction errors for the \maps and \plancks space missions, as well as the robustness of the \plancks outcome to possible failures of specific spectral channels or global variations of the detectors noise level across spectral channels.Comment: 56 pages, 21 figures made of 60 panels (files), submitted to New Astronomy, Available with all figures, at full resolution, at ftp://ftp.iap.fr/pub/from_users/bouchet/wiener7.ps.gz (1.56 Mo

The COBRAS/SAMBA CMB Project

COBRAS/SAMBA is a second generation satelitte dedicated to mapping at high resolution and sensitivity the anisotropies of the Cosmic Microwave Background (CMB). This mission is in the assessment study phase (A) at ESA, with a decision expected mid 1996, for a launch around 2003.Comment: PostScript, 4 pages, 4 figures in text, to appear in the Proceedings of the 1995 Moriond Meeting on ``Clustering in the Universe'

Simulations of the Microwave Sky and of its ``Observations''

Here follows a preliminary report on the construction of fake millimeter and sub-millimeter skies, as observed by virtual instruments, e.g. the COBRA/SAMBA mission, using theoretical modeling and data extrapolations. Our goal is to create maps as realistic as possible of the relevant physical contributions which may contribute to the detected signals. This astrophysical modeling is followed by simulations of the measurement process itself by a given instrumental configuration. This will enable a precise determination of what can and cannot be achieved with a particular experimental configuration, and provide a feedback on how to improve the overall design. It is a key step on the way to define procedures for the separation of the different physical processes in the future observed maps. Note that this tool will also prove useful in preparing and analyzing current (\eg\ balloon borne) Microwave Background experiments. Keywords: Cosmology -- Microwave Background Anisotropies.Comment: 6 pages of uuencoded compressed postscript (1.2 Mb uncompressed), to appear in the proceedings of the meeting "Far Infrared and Sub-millimeter Space Missions in the Next Decade'', Paris, France, Eds. M. Sauvage, Space Science Revie