The detection of primordial gravity waves created during the Big Bang ranks among the greatest potential intellectual achievements in modern science. During the last few decades, the instrumental progress necessary to achieve this has been nothing short of breathtaking, and we are today able to measure the microwave sky with better than one-in-a-million precision. However, from the latest ultra-sensitive experiments such as BICEP2 and Planck, it is clear that instrumental sensitivity alone will not be sufficient to make a robust detection of gravitational waves. Contamination in the form of astrophysical radiation from the Milky Way, for instance thermal dust and synchrotron radiation, obscures the cosmological signal by orders of magnitude. Even more critically, though, are secondorder interactions between this radiation and the instrument characterization itself that lead to a highly non-linear and complicated problem.
In this project, we propose a ground-breaking solution to this problem that allows for joint estimation of cosmological parameters, astrophysical components, and instrument specifications. The engine of this method is called Gibbs sampling, which we have already applied extremely successfully to basic CMB component separation. The new and critical step is to apply this method to raw time-ordered observations observed directly by the instrument, as opposed to pre-processed frequency maps, thereby closing the loop between instrumental characterization, astrophysical component separation and cosmological interpretation. While representing a ~100-fold increase in input data volume, this step is unavoidable in order to break through the current foreground-induced systematics floor.
We will apply this method to observations taken by the Planck Low-Frequency Instrument (LFI) between 2009 and 2013, and deliver new state-of-the-art frequency and component maps to the cosmological community. We will also combine these new data products with similar observations from the Wilkinson Microwave Anisotropy Probe (WMAP) observations and the ground-based CBASS experiment, and demonstrate consistency and robustness across state-of-the-art experiments.
Thus, building on this base of observations, we will:
- deliver next-generation processing of Planck LFI 30, 44 and 70 GHz frequency maps.
- deliver the world’s cleanest and most sensitive full-sky estimates of polarized synchrotron emission at CMB frequencies. This new model will form a baseline for future CMB Bmode experiments searching for inflationary gravitational waves in the coming decade, as well as for scientists studying the structure and dynamics of the Milky Way.
- deliver a new likelihood code suitable for large-scale CMB polarization analysis, and use this to derive a new and robust estimate of the optical depth of reionization, one of the most critical parameters in contemporary cosmology.
- make the software necessary for time-domain analysis available to the community under an Open Science license, allowing other projects and experiments to build on and extend our work.