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Abstract We present a joint analysis of HIabsorption Zeeman measurements and the morphology of filamentary HIemission to investigate the 3D structure of the magnetic field in the diffuse neutral interstellar medium. Our analysis is based on the Arecibo Millennium Survey and new data from the Five-hundred-meter Aperture Spherical radio Telescope toward radio sources 3C 75, 3C 207, and 3C 409. Toward 3C 409, we make a 4σZeeman detection and inferBLOS = 9.1 ± 1.9μG, in agreement with Arecibo results. We quantify the dispersion of HIfilaments at the locations and velocities of Zeeman components using GALFA-HInarrow-channel emission maps. Focusing on a subsample of 42 spectrally distinct components, we find a weak but statistically significant positive correlation (Spearmanρ= 0.3,p= 0.01) between ∣BLOS∣ and the circular variance of HIfilament orientation angles. To examine its origin, we characterize the environments probed by HIabsorption using dust emission, 3D dust maps, OH absorption, and CO emission. We find evidence that existing HIabsorption Zeeman measurements trace magnetic fields that are coherent on parsec scales, probe primarily local gas (100–500 pc, often at distances consistent with the Local Bubble wall), and exhibit systematic differences in the magnitude ofBLOS. We attribute the correlation between Zeeman measurements and filamentary HImorphology to large-scale variations in magnetic field strength and/or inclination angle across different Galactic environments, which could arise due to the Local Bubble geometry or enhanced total field strength in denser regions.
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Filamentary Dust Polarization and the Morphology of Neutral Hydrogen Structures
Filamentary structures in neutral hydrogen (Hi) emission are well aligned with the interstellar magnetic field, so Hiemission morphology can be used to construct templates that strongly correlate with measurements of polarized thermal dust emission. We explore how the quantification of filament morphology affects this correlation. We introduce a new implementation of the Rolling Hough Transform (RHT) using spherical harmonic convolutions, which enables efficient quantification of filamentary structure on the sphere. We use this Spherical RHT algorithm along with a Hessian-based method to construct Hi-based polarization templates. We discuss improvements to each algorithm relative to similar implementations in the literature and compare their outputs. By exploring the parameter space of filament morphologies with the Spherical RHT, we find that the most informative Histructures for modeling the magnetic field structure are the thinnest resolved filaments. For this reason, we find a ∼10% enhancement in theB-mode correlation with polarized dust emission with higher-resolution Hiobservations. We demonstrate that certain interstellar morphologies can produce parity-violating signatures, i.e., nonzeroTBandEB, even under the assumption that filaments are locally aligned with the magnetic field. Finally, we demonstrate thatBmodes from interstellar dust filaments are mostly affected by the topology of the filaments with respect to one another and their relative polarized intensities, whereasEmodes are mostly sensitive to the shapes of individual filaments.
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- Award ID(s):
- 2106607
- PAR ID:
- 10562542
- Publisher / Repository:
- The Astrophysical Journal
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 961
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 29
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/1538-4357/ad06aa
