Magnetic Misalignment of Interstellar Dust Filaments

Abstract

Abstract We present evidence for scale-independent misalignment of interstellar dust filaments and magnetic fields. We estimate the misalignment by comparing millimeter-wave dust-polarization measurements from Planck with filamentary structures identified in neutral-hydrogen (H i ) measurements from H i 4PI. We find that the misalignment angle displays a scale independence (harmonic coherence) for features larger than the H i 4PI beamwidth (16.′2). We additionally find a spatial coherence on angular scales of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic"></mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>°</mml:mo> <mml:mo stretchy="false">)</mml:mo> </mml:math> . We present several misalignment estimators formed from the auto- and cross-spectra of dust-polarization and H i -based maps, and we also introduce a map-space estimator. Applied to large regions of the high-Galactic-latitude sky, we find a global misalignment angle of ∼2°, which is robust to a variety of masking choices. By dividing the sky into small regions, we show that the misalignment angle correlates with the parity-violating TB cross-spectrum measured in the Planck dust maps. The misalignment paradigm also predicts a dust EB signal, which is of relevance in the search for cosmic birefringence but as yet undetected; the measurements of EB are noisier than those of TB , and our correlations of EB with misalignment angle are found to be weaker and less robust to masking choices. We also introduce an H i -based dust-polarization template constructed from the Hessian matrix of the H i intensity, which is found to correlate more strongly than previous templates with Planck dust B modes.

Topics & Concepts