Fingerprint of Galactic Loop I on polarized microwave foregrounds

Abstract

Context. Currently, detection of the primordial gravitational waves using the B-mode of cosmic microwave background (CMB) is primarily limited by our knowledge of the polarized microwave foreground emissions. Improvements of the foreground analysis are therefore necessary. As we revealed in an earlier paper, the E-mode and B-mode of the polarized foreground have noticeably different properties, both in morphology and frequency spectrum, suggesting that they arise from different physicalprocesses, and need to be studied separately. Aims. I study the polarized emission from Galactic loops, especially Loop I, and mainly focus on the following questions: Does the polarized loop emission contribute predominantly to the E-mode or B-mode? In which frequency bands and in which sky regions can the polarized loop emission be identified? Methods. Based on a well known result concerning the magnetic field alignment in supernova explosions, a theoretical expectation is established that the loop polarizations should be predominantly E-mode. In particular, the expected polarization angles of Loop I are compared with those from the real microwave band data of WMAP and Planck. Results and conclusions. The comparison between model and data shows remarkable consistency between the data and our expectations at all bands and for a large area of the sky. This result suggests that the polarized emission of Galactic Loop I is a major polarized component in all microwave bands from 23 to 353 GHz, and a considerable part of the polarized foreground likely originates from a local bubble associated with Loop I, instead of the far more distant Galactic emission. This result also provides a possible way to explain the E-to-B excess problem by contribution of the loops. Finally, this work may also provide the first geometrical evidence that the Earth was hit by a supernova explosion.