Is there a left-handed magnetic field in the solar neighborhood? Exploring helical magnetic fields in the interstellar medium through dust polarization power spectra

Abstract

The full-sky Planck polarization data at 850um revealed unexpected properties of the E and B mode power spectra of dust emission in the interstellar medium (ISM). The positive cross-correlation between the total dust intensity, T, with the B modes has raised new questions about the physical mechanisms that affect dust polarization, such as the Galactic magnetic-field structure. This is key both to better understanding ISM dynamics and to accurately describing Galactic foregrounds to the polarization of the Cosmic Microwave Background (CMB). In this theoretical paper we investigate the possibility that the observed cross-correlations in the dust polarization power spectra, and specifically between T and B, can be related to a parity-odd quantity in the ISM such as the magnetic helicity. We produce synthetic dust polarization data, derived from 3D analytical toy models of density structures and helical magnetic fields, to compare with the E and B modes of observations. Focusing on the observed T-B correlation, we propose a new line of interpretation of the Planck observations based on a large-scale helical component of the Galactic magnetic field in the solar neighborhood. Our analysis shows that: I) the sign of magnetic helicity does not affect E and B modes for isotropic magnetic-field configurations; II) helical magnetic fields threading interstellar filaments cannot reproduce the Planck results; III) a weak helical left-handed magnetic field structure in the solar neighborhood may explain the T-B correlation seen in the Planck data. This work suggests a new perspective for the interpretation of the dust polarization power spectra, which strongly supports the imprint of a large-scale structure of the Galactic magnetic field in the solar neighborhood.

arXiv commentAccepted by Astronomy & Astrophysics on November 24, 2018

References in corpus (39)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• An All-Sky Analysis of Polarization in the Microwave Background
• A Joint Analysis of BICEP2/Keck Array and Planck Data
• Signature of Gravity Waves in Polarization of the Microwave Background
• A Probe of Primordial Gravity Waves and Vorticity
• The LOFAR Two-metre Sky Survey - II. First data release
• Radiative torques: Analytical Model and Basic Properties
• Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust
• Extending Big Power Law in the Sky with Turbulence Spectra from WHAM data
• Magnetic Helicity Conservation and Astrophysical Dynamos
• Planck intermediate results. XXX. The angular power spectrum of polarized dust emission at intermediate and high Galactic latitudes
• Planck 2018 results. XI. Polarized dust foregrounds
• Planck intermediate results. XX. Comparison of polarized thermal emission from Galactic dust with simulations of MHD turbulence
• A unified model of grain alignment: radiative alignment of interstellar grains with magnetic inclusions
• Galactic dynamo and helicity losses through fountain flow
• Astrophysical hydromagnetic turbulence
• Neutral hydrogen structures trace dust polarization angle: Implications for cosmic microwave background foregrounds
• Polarized Sub-Millimetre Emission from Filamentary Molecular Clouds
• Tracing magnetic fields with spectroscopic channel maps
• Galactic dynamos supported by magnetic helicity fluxes
• Alignment of Irregular Grains by Mechanical Torques
• The nature of the E-B decomposition of CMB polarization
• Search for CP Violating Signature of Intergalactic Magnetic Helicity in the Gamma Ray Sky
• Strong mean field dynamos require supercritical helicity fluxes
• The Local Bubble: a magnetic veil to our Galaxy
• Helical Magnetic Fields in Molecular Clouds? A New Method to Determine the Line-of-Sight Magnetic Field Structure in Molecular Clouds
• Dust-polarization maps for local interstellar turbulence
• Dust polarization and ISM turbulence
• Primordial Magnetic Helicity Constraints from WMAP Nine-Year Data
• PASIPHAE: A high-Galactic-latitude, high-accuracy optopolarimetric survey
• Can the observed E/B ratio for dust galactic foreground be explained by sub-Alfvenic turbulence?
• Statistical properties of galactic CMB foregrounds: dust and synchrotron
• CMB EB and TB cross-spectrum estimation via pseudo-spectrum techniques
• Tensor Anisotropies in an Open Universe
• Magnetic Fields in Star-Forming Molecular Clouds IV. Polarimetry of the Filamentary NGC 2068 Cloud in Orion B
• Polytropic models of filamentary interstellar clouds -II. Helical magnetic fields
• POKER: Estimating the power spectrum of diffuse emission with complex masks and at high angular resolution
• A new perspective on turbulent Galactic magnetic fields through comparison of linear polarisation decomposition techniques
• Multi-Scale Analysis of Magnetic Fields in Filamentary Molecular Clouds in Orion A

Cited by in corpus (17)

• The Origin of Parity Violation in Polarized Dust Emission and Implications for Cosmic Birefringence
• The Galactic Faraday depth sky revisited
• The Power Spectra of Polarized, Dusty Filaments
• Compressed magnetized shells of atomic gas and the formation of the Corona Australis molecular cloud
• Frequency dependence of the thermal dust $E/B$ ratio and $EB$ correlation: insights from the spin-moment expansion
• Magnetic Misalignment of Interstellar Dust Filaments
• A Unified Model for the Fan Region and the North Polar Spur: A bundle of filaments in the Local Galaxy
• hammurabi X: Simulating Galactic Synchrotron Emission with Random Magnetic Fields
• The link between E-B polarization modes and gas column density from interstellar dust emission
• Modeling parity-violating spectra in Galactic dust polarization with filaments and its applications to cosmic birefringence searches
• Batchelor, Saffman, and Kazantsev spectra in galactic small-scale dynamos
• A global two-scale helicity proxy from $\pi$-ambiguous solar magnetic fields
• Polarization power spectra and dust cloud morphology
• The effect of cosmic variance on the characteristics of dust polarization power spectra
• Application of a helicity proxy to edge-on galaxies
• The Galactic interstellar medium has a preferred handedness of magnetic misalignment
• Hemispheric handedness in the Galactic synchrotron polarization foreground