Link between E–B polarization modes and gas column density from interstellar dust emission

Abstract

Context. The analysis of the Planck polarization E and B mode power spectra of interstellar dust emission at 353 GHz recently raised new questions on the impact of Galactic foregrounds to the detection of the polarization of the Cosmic Microwave Background (CMB) and on the physical properties of the interstellar medium (ISM). In the diffuse ISM at high-latitude a clear E − B asymmetry is observed, with twice as much power in E modes than in B modes; as well as a positive correlation between the total power, T , and both E and B modes, presently interpreted in terms of the link between the structure of interstellar matter and that of the Galactic magnetic field. Aims. In this paper we aim at extending the Planck analysis of the high-latitude sky to low Galactic latitude, investigating the correlation between the T -E-B auto-and cross-correlation power spectra with the gas column density from the diffuse ISM to molecular clouds. Methods. We divide the sky between Galactic latitude |b| > 5 • and |b| < 60 • in 552 circular patches, with an area of ∼400 •2 , and we study the cross-correlations between the T -E-B power spectra and the column density of each patch using the latest release of the Planck polarization data. Results. We find that the B-to-E power ratio (D BB /D EE ) and the T E correlation ratio (r T E ) depend on column density. While the former increases going from the diffuse ISM to molecular clouds in the Gould Belt, the latter decreases. This systematic variation must be related to actual changes in ISM properties. The data show significant scatter about this mean trend. The variations of D BB /D EE and r T E are observed to be anti-correlated for all column densities. In the diffuse ISM, the variance of these two ratios is consistent with a stochastic non-Gaussian model in which the values of D BB /D EE and r T E are fixed. We finally discuss the dependencies of T B and EB with column density, which are however hampered by instrumental noise. Conclusions. For the first time, this work shows significant variations of the T -E-B power spectra of dust polarized emission across a large fraction of the Galaxy. Their dependence on multipole and gas column density is key for accurate forecasts of next generation CMB experiments and for constraining present models of ISM physics (i.e., dust properties and interstellar turbulence) that are considered responsible for the observed T -E-B signals.

CMB as thermal radiation from cosmic dust grains in equilibrium with the redshifted starlight

“…It is clearly shown in the map of Figure 14 and it is fully independent on the spatial origin of the CMB, as the radiation can only reach the WMAP satellite position (across the Lagrangian point L2 in the Earth proximity) by crossing the Milky Way. On the contrary, as support of the previous statement, the B-Mode nature found in the polarization, unequivocally associates the polarization map to our galaxy [53]. By folding back the map into a spherical shape, the meaning of the orientation of the polarization takes shape.…”

The Origin of Parity Violation in Polarized Dust Emission and Implications for Cosmic Birefringence

“…To investigate these correlations in Planck data, we tile the sky with 12 • radius circular regions centered on N side =8 HealPix pixels (Górski et al 2005), additionally applying our fiducial mask, and apodize each region with a 2 • cosine taper (similar to analyses in Planck Collaboration Int. XXX 2016; Krachmalnicoff et al 2018;Bracco et al 2019b). We compute cross-correlations between T 857 , E 353 , and B 353 , using splits of the NPIPE data as in the preceding analysis.…”

“…A magnetic field oriented orthogonally to the main axis of a filament would produce polarized emission with a negative T E correlation (Zaldarriaga 2001;Huffenberger et al 2020). It is thus reasonable to expect that high column density regions of sky might have negative T E (Bracco et al 2019b). This could be tested in measurements of dust emission at higher angular resolution, with ∼arcminute-resolution dust polarization maps made by ground-based CMB experiments like the Atacama Cosmology Telescope (Aiola et al 2020;Naess et al 2020) and the South Pole Telescope (Benson et al 2014), as well as next-generation or proposed experiments like the Simons Observatory (Ade et al 2019), CMB-S4 (Abazajian et al 2016(Abazajian et al , 2019, CCAT-prime (Choi et al 2020a), and PICO (Hanany et al 2019).…”

“…Based on our findings, one well-motivated strategy for searches for an isotropic cosmic birefringence angle is to build masks that restrict the Galactic emission to a single sign of T E and T B, in order to simplify the expectation for the foreground EB. Because T E is generally positive in the diffuse ISM, this approach motivates the exclusion of high-column density sightlines that carry a reasonable astrophysical expectation of a negative T E signal (e.g., Bracco et al 2019b). Otherwise, the anticorrelation between T B and EB in regions where T E < 0 will complicate estimation of the global EB signal that relies on T B and T E.…”

Dust Polarization Maps from TIGRESS: E/B Power Asymmetry and TE Correlation

“…In the same analysis, E-mode polarization shows a positive correlation with temperature anisotropy (T E correlation). EB correlations are statistically insignificant but there are recent claims of a weak positive T B correlation (Planck Collaboration et al 2018;Bracco et al 2019).…”