An Imprint of the Galactic Magnetic Field in the Diffuse Unpolarized Dust Emission

Hensley, Brandon; Zhang, Cheng; Bock, J. J.

doi:10.3847/1538-4357/ab5183

Cited by 22 publications

(17 citation statements)

References 61 publications

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“…This correlation is true for a given column density. The correlation is therefore not driven by the fitting degeneracy between T d and dust amplitude at low signal-to-noise ratio regions that was discussed in Hensley et al (2019).…”

Section: Are Ivcs Important For Polarized Cmb Foregroundmentioning

confidence: 80%

“…The morphological patterns that appear on the maps under investigation typically cover sky areas much larger than the pixel size at any of these resolutions. Averaging model parameters in this way is only used here for investigating such large-scale spatial correlations (see also Hensley et al 2019).…”

Section: Signatures Of Ivcs In Planck Dust Emissionmentioning

confidence: 99%

“…A simple correlation of T d and N H IVC Iyields the very small Pearson correlation coefficient of 0.2. However, we need to take into account that T d is also found to correlate with the total N H I , as discussed byHensley et al (2019). If IVC intrinsic properties are responsible for the change in T d , then we should expect that sight lines with stronger IVC emission show a…”

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confidence: 99%

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Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Panopoulou

Lenz

2020

ApJ

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Characterizing the structure of the Galactic interstellar medium (ISM) in three dimensions is of high importance for accurate modeling of dust emission as a foreground to the cosmic microwave background (CMB). At high Galactic latitude, where the total dust content is low, accurate maps of the 3D structure of the ISM are lacking. We develop a method to quantify the complexity of the distribution of dust along the line of sight with the use of H I line emission. The method relies on a Gaussian decomposition of the H I spectra to disentangle the emission from overlapping components in velocity. We use this information to create maps of the number of clouds along the line of sight. We apply the method to (a) the high Galactic latitude sky and (b) the region targeted by the BICEP/Keck experiment. In the north Galactic cap we find on average three clouds per 0.2 square degree pixel, while in the south the number falls to 2.5. The statistics of the number of clouds are affected by intermediate-velocity clouds (IVCs), primarily in the north. IVCs produce detectable features in the dust emission measured by Planck. We investigate the complexity of H I spectra in the BICEP/Keck region and find evidence for the existence of multiple components along the line of sight. The data (doi: 10.7910/DVN/8DA5LH) and software are made publicly available and can be used to inform CMB foreground modeling and 3D dust mapping.Unified Astronomy Thesaurus concepts: Interstellar medium (847); Neutral hydrogen clouds (1099); Interstellar atomic gas (833)

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Section: Are Ivcs Important For Polarized Cmb Foregroundmentioning

confidence: 80%

Section: Signatures Of Ivcs In Planck Dust Emissionmentioning

confidence: 99%

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confidence: 99%

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Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Panopoulou

Lenz

2020

ApJ

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“…Let us divide the LOS into N clouds such that the ith cloud has column density N i HI . Then the observed Stokes parameters of the polarized dust emission at a frequency ν are given by (e.g., Hensley et al 2019):…”

Section: Estimation Of Required Sed Variationmentioning

confidence: 99%

Evidence for line-of-sight frequency decorrelation of polarized dust emission in Planck data

Pelgrims

Clark

Hensley

et al. 2021

A&A

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If a single line of sight (LOS) intercepts multiple dust clouds with different spectral energy distributions and magnetic field orientations, then the frequency scaling of each of the Stokes Q and U parameters of the thermal dust emission may be different, a phenomenon we refer to as LOS frequency decorrelation. We present first evidence for LOS frequency decorrelation in Planck data using independent measurements of neutral-hydrogen (HI) emission to probe the 3D structure of the magnetized interstellar medium (ISM). We use HI-based measurements of the number of clouds per LOS and the magnetic field orientation in each cloud to select two sets of sightlines: (i) a target sample of pixels that are likely to exhibit LOS frequency decorrelation and (ii) a control sample of pixels that lack complex LOS structure. We test the null hypothesis that LOS frequency decorrelation is not detectable in Planck 353 and 217 GHz polarization data at high Galactic latitudes. We reject the null hypothesis at high significance based on data that show that the combined effect of polarization angle variation with frequency and depolarization are detected in the target sample. This detection is robust against the choice of cosmic microwave background (CMB) map and map-making pipeline. The observed change in polarization angle due to LOS frequency decorrelation is detectable above the Planck noise level. The probability that the detected effect is due to noise alone ranges from 5 × 10−2 to 4 × 10−7, depending on the CMB subtraction algorithm and treatment of residual systematic errors; correcting for residual systematic errors consistently increases the significance of the effect. Within the target sample, the LOS decorrelation effect is stronger for sightlines with more misaligned magnetic fields, as expected. With our sample, we estimate that an intrinsic variation of ~15% in the ratio of 353 to 217 GHz polarized emission between clouds is sufficient to reproduce the measured effect. Our finding underlines the importance of ongoing studies to map the three-dimensional structure of the magnetized and dusty ISM that could ultimately help component separation methods to account for frequency decorrelation effects in CMB polarization studies.

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“…Computing the polarized emission properties of dust grains is a complex and computationally challenging problem. Therefore, models of polarized dust emission either focus on a limited number of alignment mechanisms and/or make strong assumptions about the degree of alignment (e.g., perfect alignment) and the type and shape of aligned grains (e.g., Pelkonen et al 2007Pelkonen et al , 2009Siebenmorgen et al 2014;Reissl et al 2016;Hensley et al 2019). However, new planned observational facilities offer a prospect of a much larger volume of polarimetric data on various scales, and this prompts the development of more advanced tools that can provide the material properties that are required to accurately model polarization within forward radiation transfer (RT) modeling.…”

Section: Introductionmentioning

confidence: 99%

CosTuuM: Polarized Thermal Dust Emission by Magnetically Oriented Spheroidal Grains

Vandenbroucke

Baes

Camps

2020

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We present the new open-source C++-based Python library COSTUUM that can be used to generate infrared absorption and emission coefficients for arbitrary mixtures of spheroidal dust grains that are (partially) aligned with a magnetic field. We outline the algorithms underlying the software, demonstrate the accuracy of our results using benchmarks from literature, and use our tool to investigate some commonly used approximative recipes. We find that the linear polarization fraction for a partially aligned dust grain mixture can be accurately represented by an appropriate linear combination of perfectly aligned grains and grains that are randomly oriented, but that the commonly used picket fence alignment breaks down for short wavelengths. We also find that for a fixed dust grain size, the absorption coefficients and linear polarization fraction for a realistic mixture of grains with various shapes cannot both be accurately represented by a single representative grain with a fixed shape, but that instead an average over an appropriate shape distribution should be used. Insufficient knowledge of an appropriate shape distribution is the main obstacle in obtaining accurate optical properties. COSTUUM is available as a standalone Python library and can be used to generate optical properties to be used in radiative transfer applications.

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An Imprint of the Galactic Magnetic Field in the Diffuse Unpolarized Dust Emission

Cited by 22 publications

References 61 publications

Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Evidence for line-of-sight frequency decorrelation of polarized dust emission in Planck data

CosTuuM: Polarized Thermal Dust Emission by Magnetically Oriented Spheroidal Grains

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