Mapping the Magnetic Interstellar Medium in Three Dimensions over the Full Sky with Neutral Hydrogen

Clark, Susan; Hensley, Brandon

doi:10.3847/1538-4357/ab5803

Cited by 93 publications

(170 citation statements)

References 125 publications

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“…This approach differs from previous work where dust polarization maps are computed from a phenomenological model and ancillary observations (Planck Collaboration Int. XLII 2016; Ghosh et al 2017;Vansyngel et al 2017;Levrier et al 2018;Adak et al 2020;Clark & Hensley 2019) or directly from numerical simulations (Kim et al 2019). It follows what has been done for dust total intensity by Allys et al (2019) using the RWST, and Aylor et al (2019) using a Generative Adversarial Network.…”

Section: Random Syntheses Ofq + Iũ Polarization Mapsmentioning

confidence: 81%

Statistical description of dust polarized emission from the diffuse interstellar medium

Blancard

Levrier

Allys

et al. 2020

A&A

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The statistical characterization of the diffuse magnetized interstellar medium (ISM) and Galactic foregrounds to the cosmic microwave background (CMB) poses a major challenge. To account for their non-Gaussian statistics, we need a data analysis approach capable of efficiently quantifying statistical couplings across scales. This information is encoded in the data, but most of it is lost when using conventional tools, such as one-point statistics and power spectra. The wavelet scattering transform (WST), a low-variance statistical descriptor of non-Gaussian processes introduced in data science, opens a path towards this goal. To establish the methodology, we applied the WST to noise-free maps of dust polarized thermal emission computed from a numerical simulation of magnetohydrodynamical turbulence in the diffuse ISM. We analyzed normalized complex Stokes maps and maps of the polarization fraction and polarization angle. The WST yields a few thousand coefficients; some of them measure the amplitude of the signal at a given scale, and the others characterize the couplings between scales and orientations. The dependence on orientation can be fitted with the reduced wavelet scattering transform (RWST), an angular model introduced in previous works for total intensity maps. The RWST provides a statistical description of the polarization maps, quantifying their multiscale properties in terms of isotropic and anisotropic contributions. It allowed us to exhibit the dependence of the map structure on the orientation of the mean magnetic field and to quantify the non-Gaussianity of the data. We also used RWST coefficients, complemented by additional constraints, to generate random synthetic maps with similar statistics. Their agreement with the original maps demonstrates the comprehensiveness of the statistical description provided by the RWST. This work is a step forward in the analysis of observational data and the modeling of CMB foregrounds. We also release PyWST, a public Python package to perform WST and RWST analyses of two-dimensional data.

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Section: Random Syntheses Ofq + Iũ Polarization Mapsmentioning

confidence: 81%

Statistical description of dust polarized emission from the diffuse interstellar medium

Blancard

Levrier

Allys

et al. 2020

A&A

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“…The distribution of the magnetic fields is complex but again related to the morphology of matter distribution in our galaxy. It has been shown that the integrated intensity maps processed with a rolling Hough transform [30] correlate significantly with the dust polarization angle [13,16]. However, the use of Hough transform in that work was purely phenomenological.…”

Section: Discussionmentioning

confidence: 99%

“…Hence, a natural extension of Refs. [13,16] would be to replace the integrated intensity maps with the full velocity cube and the Hough transform with a neural network in order to learn the necessary transformation. We leave this for future work.…”

Section: Discussionmentioning

confidence: 99%

“…However, the 21 cm dataset is considerably richer: the line is well resolved by modern surveys giving the full velocity structure of the hydrogen along the line-of-sight -at each spatial position one can measure the full profile of the velocity line. It is entirely plausible that the full information about the velocity structure along the line-of-sight encodes information about the physical environment in which the neutral hydrogen exists and can therefore be useful in inferring the dust polarization angle [14][15][16]. In this paper we explore this possibility in a way that does not assume any concrete physical model but uses existing data to see if dust can be predicted from many maps corresponding to velocity slices in 21 cm measurement using modern machine-learning techniques.…”

Section: Introductionmentioning

confidence: 99%

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Predicting dust emission using galactic 21 cm data

Zhang¹,

Chiang²,

Sheehy³

et al. 2019

J. Cosmol. Astropart. Phys.

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Understanding large-angular-scale galactic foregrounds is crucial for future CMB experiments aiming to detect B-mode polarization from primordial gravitational waves. Traditionally, the dust component has been separated using its different frequency dependence. However, using non-CMB observations has potential to increase fidelity and decrease the reconstruction noise. In this exploratory paper we investigate the capability of galactic 21 cm observations to predict the dust foreground in intensity. We train a neural network to predict the dust foreground as measured by the Planck Satellite from the full velocity data-cube of galactic 21 cm emission as measured by the HI4PI survey. We demonstrate that information in the velocity structure clearly improves the predictive power over both a simple integrated emission model and a simple linear model. The improvement is significant at arc-minute scales but more modest at degree scales. This proof of principle on temperature data indicates that it might also be possible to improve foreground polarization templates from the same input data.

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“…Specifically, we use HI emission data to identify sightlines that are potentially most susceptible to this effect. We combine information on the discrete number of HI clouds on each sightline (Panopoulou & Lenz 2020) with an estimate of the magnetic field orientation in each cloud inferred from the morphology of linear HI structures (Clark & Hensley 2019). This entirely HI-based sample selection is "agnostic" to the Planck dust polarization data.…”

Section: Introductionmentioning

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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Mapping the Magnetic Interstellar Medium in Three Dimensions over the Full Sky with Neutral Hydrogen

Cited by 93 publications

References 125 publications

Statistical description of dust polarized emission from the diffuse interstellar medium

Statistical description of dust polarized emission from the diffuse interstellar medium

Predicting dust emission using galactic 21 cm data

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

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