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Abstract Utilizing Planck polarized dust emission maps at 353 GHz and large-area maps of the neutral hydrogen (Hi) cold neutral medium (CNM) fraction (fCNM), we investigate the relationship between dust polarization fraction (p353) andfCNMin the diffuse high latitude ( ) sky. We find that the correlation betweenp353andfCNMis qualitatively distinct from thep353–Hicolumn density (NHi) relationship. At low column densities (NHi< 4 × 1020cm−2) wherep353andNHiare uncorrelated, there is a strong positivep353–fCNMcorrelation. We fit thep353–fCNMcorrelation with data-driven models to constrain the degree of magnetic field disorder between phases along the line of sight. We argue that an increased magnetic field disorder in the warm neutral medium (WNM) relative to the CNM best explains the positivep353–fCNMcorrelation in diffuse regions. Modeling the CNM-associated dust column as being maximally polarized, with a polarization fractionpCNM∼ 0.2, we find that the best-fit mean polarization fraction in the WNM-associated dust column is 0.22pCNM. The model further suggests that a significantfCNM-correlated fraction of the non-CNM column (an additional 18.4% of the Himass on average) is also more magnetically ordered, and we speculate that the additional column is associated with the unstable medium. Our results constitute a new large-area constraint on the average relative disorder of magnetic fields between the neutral phases of the interstellar medium, and are consistent with the physical picture of a more magnetically aligned CNM column forming out of a disordered WNM.
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Mid-infrared Polarization of the Diffuse Interstellar Medium toward CygOB2-12
Abstract We present the first mid-IR detection of the linear polarization toward the star CygOB2-12, a luminous blue hypergiant that, withAV≈ 10 mag of foreground extinction, is a benchmark in the study of the properties of dust in the diffuse interstellar medium. The 8–13μm spectropolarimetry, obtained with the CanariCam multimode camera at the Gran Telescopio CANARIAS shows clear trends with wavelength characteristic of silicate grains aligned in the interstellar magnetic field. The maximum polarization, detected with 7.8σstatistical significance near 10.2μm, is (1.24 ± 0.28)% with position angle 126° ± 8°. We comment on these measurements in the context of recent models for the dust composition in the diffuse interstellar medium.
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- Award ID(s):
- 1908625
- PAR ID:
- 10381334
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 940
- Issue:
- 1
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L26
- Size(s):
- Article No. L26
- Sponsoring Org:
- National Science Foundation
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