Characterization of foreground emission on degree angular scales for CMB B-mode observations

Thermal dust and synchrotron signal from Planck and WMAP data

¹ Dipartimento di FisicaUniversità degli Studi di Milano, via Celoria, 16, 20133 Milano, Italy
e-mail: nicoletta.krachmalnicoff@unimi.it
² INAF/IASF Milano, via E. Bassini, 15, 20133 Milano, Italy
³ SISSA, Astrophysics Sector, via Bonomea 265, 34136 Trieste, Italy
⁴ INFN, via Valerio 2, 34127 Trieste, Italy
⁵ Institut d’Astrophysique Spatiale, CNRS (UMR 8617) Université Paris-Sud 11, Bâtiment 121, 91405 Orsay, France

Received: 2 November 2015
Accepted: 28 January 2016

Abstract

We quantify the contamination from polarized diffuse Galactic synchrotron and thermal dust emissions to the B modes of the cosmic microwave background (CMB) anisotropies on the degree angular scale, using data from the Planck and Wilkinson Microwave Anisotropy Probe (WMAP) satellites. We compute power spectra of foreground polarized emissions in 352 circular sky patches located at Galactic latitude | b | > 20°, each of which covers about 1.5% of the sky. We make use of the spectral properties derived from Planck and WMAP data to extrapolate, in frequency, the amplitude of synchrotron and thermal dust B-mode spectra in the multipole bin centered at ℓ ≃ 80. In this way we estimate the amplitude and frequency of the foreground minimum for each analyzed region. We detect both dust and synchrotron signal on degree angular scales and at a 3σ confidence level in 28 regions. Here the minimum of the foreground emission is found at frequencies between 60 and 100 GHz with an amplitude expressed in terms of the equivalent tensor-to-scalar ratio, r_FG,min, between ~0.06 and ~1. Some of these regions are located at high Galactic latitudes in areas close to the ones that are being observed by suborbital experiments. In all the other sky patches where synchrotron or dust B modes are not detectable with the required confidence, we put upper limits on the minimum foreground contamination and find values of r_FG,min between ~0.05 and ~1.5 in the frequency range 60–90 GHz. Our results indicate that, with the current sensitivity at low frequency, it is not possible to exclude the presence of synchrotron contamination to CMB cosmological B modes at the level requested to measure a gravitational waves signal with r ≃ 0.01 at frequency ≲100 GHz anywhere. Therefore, more accurate data are essential in order to better characterize the synchrotron polarized component and, eventually, to remove its contamination to CMB signal through foreground cleaning.