Issue |
A&A
Volume 503, Number 3, September I 2009
|
|
---|---|---|
Page(s) | 691 - 706 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361/200911624 | |
Published online | 27 May 2009 |
Measuring the tensor to scalar ratio from CMB B-modes in the presence of foregrounds
1
AstroParticule et Cosmologie (APC), CNRS: UMR 7164, Université Denis Diderot, Paris 7, Observatoire de Paris, France e-mail: betoule@apc.univ-paris7.fr
2
University of Southern California, Los Angeles, CA 90089-0484, USA
Received:
7
January
2009
Accepted:
7
May
2009
Aims. We investigate the impact of polarised foreground emission on the performances of future CMB experiments aiming to detect primordial tensor fluctuations in the early universe. In particular, we study the accuracy that can be achieved in measuring the tensor-to-scalar ratio r in the presence of foregrounds.
Methods. We designed a component separation pipeline, based on the Smica method, aimed at estimating r and the foreground contamination from the data with no prior assumption on the frequency dependence or spatial distribution of the foregrounds. We derived error bars accounting for the uncertainty on foreground contribution. We used the current knowledge of galactic and extra-galactic foregrounds as implemented in the Planck sky model (PSM) to build simulations of the sky emission. We applied the method to simulated observations of this modelled sky emission, for various experimental setups. Instrumental systematics are not considered in this study.
Results. Our method, with Planck data, permits us to detect from
B-modes only at more than 3σ. With a future dedicated space
experiment, such as EPIC, we can measure
at ∼
for
the most ambitious mission designs. Most of the sensitivity to r
comes from scales
for high r values,
shifting to lower
's for progressively smaller r. This shows
that large-scale foreground emission does not prevent proper
measurement of the reionisation bump for full sky experiments. We
also investigate the observation of a small but clean part of the
sky. We show that diffuse foregrounds remain a concern for a
sensitive ground-based experiment with a limited frequency coverage
when measuring
. Using the Planck data as additional
frequency channels to constrain the foregrounds in such
ground–based observations reduces the error by a factor two but
does not allow detection of
. An alternate strategy, based on
a deep field space mission with a wide frequency coverage, would
allow us to deal with diffuse foregrounds efficiently, but is in
return quite sensitive to lensing contamination. In contrast,
we show that all-sky missions are nearly insensitive to small-scale
contamination (point sources and lensing) if the statistical
contribution of such foregrounds can be modelled accurately. Our
results do not significantly depend on the overall level and
frequency dependence of the diffused foreground model, when varied
within the limits allowed by current observations.
Key words: cosmology: cosmic microwave background / cosmology: cosmological parameters / cosmology: observations
© ESO, 2009
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