Foreground component separation with generalised ILC

The 'Internal Linear Combination' (ILC) component separation method has been extensively used to extract a single component, the CMB, from the WMAP multifrequency data. We generalise the ILC approach for separating other millimetre astrophysical emissions. We construct in particular a multidimensional ILC filter, which can be used, for instance, to estimate the diffuse emission of a complex component originating from multiple correlated emissions, such as the total emission of the Galactic interstellar medium. The performance of such generalised ILC methods, implemented on a needlet frame, is tested on simulations of Planck mission observations, for which we successfully reconstruct a low noise estimate of emission from astrophysical foregrounds with vanishing CMB and SZ contamination.Comment: 11 pages, 6 figures (2 figures added), 1 reference added, introduction expanded, V2: version accepted by MNRA

A needlet ILC analysis of WMAP 9-year polarisation data: CMB polarisation power spectra

We estimate Cosmic Microwave Background (CMB) polarisation power spectra, and temperature-polarisation cross-spectra, from the 9-year data of the Wilkinson Microwave Anisotropy Probe (WMAP). Foreground cleaning is implemented using minimum variance linear combinations of the coefficients of needlet decompositions of sky maps for all WMAP channels, to produce maps for CMB temperature anisotropies (T-mode) and polarisation (E-mode and B-mode), for 9 different years of observation. The final power spectra are computed from averages of all possible cross-year power spectra obtained using foreground-cleaned maps for the different years. Our analysis technique yields a measurement of the EE spectrum that is in excellent agreement with theoretical expectations from the current cosmological model. By comparison, the publicly available WMAP EE power spectrum is higher on average (and significantly higher than the predicted EE spectrum from the current best fit) at scales larger than about a degree, an excess that is not confirmed by our analysis.Comment: 13 pages, 7 figures, Significantly changed version accepted for publication in MNRA

Measuring CMB polarisation with the Planck HFI

We describe the Planck HFI design and expected performances for measuring CMB polarisation.Comment: Proceedings of the Pol2001 "Astrophysical Polarised Backgrounds" conference, Bologna, 9-12 october 200

CMB and SZ effect separation with Constrained Internal Linear Combinations

The `Internal Linear Combination' (ILC) component separation method has been extensively used on the data of the WMAP space mission, to extract a single component, the CMB, from the WMAP multifrequency data. We extend the ILC approach for reconstructing millimeter astrophysical emissions beyond the CMB alone. In particular, we construct a Constrained ILC to extract clean maps of both the CMB or the thermal Sunyaev Zeldovich (SZ) effect, with vanishing contamination from the other. The performance of the Constrained ILC is tested on simulations of Planck mission observations, for which we successfully reconstruct independent estimates of the CMB and of the thermal SZ.Comment: 7 pages, 3 figures, submitted to MNRA

Circular scans for CMB anisotropy observation and analysis

A number of experiments for measuring anisotropies of the Cosmic Microwave Background use scanning strategies in which temperature fluctuations are measured along circular scans on the sky. It is possible, from a large number of such intersecting circular scans, to build two-dimensional sky maps for subsequent analysis. However, since instrumental effects --- especially the excess low-frequency 1/f noise --- project onto such two-dimensional maps in a non-trivial way, we discuss the analysis approach which focuses on information contained in the individual circular scans. This natural way of looking at CMB data from experiments scanning on the circles combines the advantages of elegant simplicity of Fourier series for the computation of statistics useful for constraining cosmological scenarios,and superior efficiency in analysing and quantifying most of the crucial instrumental effects.Comment: 10 pages, 5 figures (.ps), submitted to MNRA