Detection of Polarized Infrared Emission by Polycyclic Aromatic Hydrocarbons in the MWC 1080 Nebula

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in astrophysical environments, as revealed by their pronounced emission features at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 $\mu$m commonly ascribed to the C--H and C--C vibrational modes. Although these features have long been predicted to be polarized, previous searches for PAH polarization led to null or, at best, tentative detections. Here we report the definite detection of polarized PAH emission at 11.3 $\mu$m in the nebula associated with the Herbig Be star MWC 1080. We measure a polarization degree of 1.9$\pm$0.2\%, which is unexpectedly high compared to models. This poses a challenge in the current understanding of the alignment of PAHs, which is required to polarize the PAH emission but thought to be substantially suppressed. PAH alignment with a magnetic field via a resonance paramagnetic relaxation process may account for such a high level of polarization.

15 pages, 3 figures, accepted by ApJ

References in corpus (6)

• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• Polycyclic Aromatic Hydrocarbon in Protoplanetary Disks around Herbig Ae/Be and T Tauri Stars
• Dense Molecular Gas In A Young Cluster Around MWC 1080 -- Rule Of The Massive Star
• Missing Fe: hydrogenated iron nanoparticles
• The Immediate Environments of Two Herbig Be Stars: MWC 1080 and HD 259431
• The Mid-Infrared Polarization of the Herbig Ae Star WL 16: An Interstellar Origin?

Cited by in corpus (7)

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• Observational Constraints on the Physical Properties of Interstellar Dust in the Post-Planck Era
• The Simons Observatory: Galactic Science Goals and Forecasts
• Two modes of carbonaceous dust alignment
• QUIJOTE Scientific results. III. Microwave spectrum of intensity and polarization in the Taurus molecular cloud Complex and L1527
• Ultraviolet Spectropolarimetry with Polstar: Interstellar Medium Science
• Modelling the mid-infrared polarization in dust around young stars