Polarized Foregrounds and the Cosmic Microwave Background

Abstract

The past year has been an exciting time for CMB cosmology, with observational efforts coming closer to a detection of primordial gravitational waves. As the upper bound on the tensor-to-scalar ratio is lowered more and more, one of the greatest challenges of cosmology is related to the efficient removal of contaminations from the Galactic foreground. In order to investigate the levels of foreground emissions, we used WMAP and Planck polarized maps, and studied the likelihood distributions of the spectral index between 100 and 150 GHz. We found that the spectral index provides a very powerful method of distinguishing between the polarized foregrounds and a potential primordial B-mode signal. However, for the relatively large fraction of the sky included in our data set, we find that the synchrotron and dust levels are too high to be able to identify with high confidence a CMB signal corresponding to r = 0.1. Choosing a cleaner test patch of the sky confirmed that a reduction in the foreground levels by a factor of ~20 can greatly improve our chances of detecting primordial gravitational waves. Nevertheless, for tensor-to-scalar ratios r << 0.1, the detection of a primordial B-mode signal will require measurements at additional frequencies.