Limits on the detectability of the CMB B-mode polarization imposed by foregrounds

Abstract

We investigate which practical constraints are imposed by foregrounds to the detection of the B-mode polarization generated by gravitational waves in the case of experiments of the type currently being planned. Because the B-mode signal is probably dominated by foregrounds at all frequencies, the detection of the cosmological component depends drastically on our ability for removing foregrounds. We provide an analytical expression to estimate the level of the residual polarization for Galactic foregrounds, according to the method employed for their subtraction. We interpret this result in terms of the lower limit of the tensor-to-scalar ratio r that allows to disentangle the cosmological B-mode polarization from the foregrounds contribution. Polarized emission from extragalactic radio sources and gravitational lensing is also taken into account. As a first approach, we consider the ideal limit of a noise--free experiment: for a full--sky coverage and a degree resolution, we obtain a limit of r~10^(-4). This value can be improved by high--resolution experiments and, in principle, no clear fundamental limit on the detectability of gravitational waves polarization is found. Our analysis is also applied to planned or hypothetical future polarization experiments, taking into account expected noise levels

A cryogenic waveplate rotator for polarimetry at mm and submm wavelengths

“…Therefore, an accurate knowledge of the polarization of these sources is necessary to perform a precise measurement of the polarized cosmological signal. This is made difficult by the small amplitude of the polarized signal of these sources and by its strong angular and wavelength dependence (Tucci et al 2005).…”

The QUIJOTE CMB Experiment

“…This is illustrated in the left panel of Fig. 2, where we present the amplitude of the expected synchrotron and radio-source contribution at 30 GHz, computed according to the models described in [14].…”

“…This information is extremely important given that B-modes are known to be sub-dominant in amplitude as compared to the Galactic emission (see e.g. [14]). This is illustrated in the left panel of Fig.…”

“…In order to achieve these scientific objectives, we need to cover a total sky area of the order of 3,000 -10,000 square degrees, and to reach sensitivities of ∼ 3 − 4 µK per one degree beam after one year of operation with the low frequency instrument (11)(12)(13)(14)(15)(16)(17)(18)(19), and 1 µK per beam with the second instrument at 30 GHz. Although the final observing strategy is still under discussion, a possible solution is presented in Fig.…”

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