Abstract
We analyze the wavelength dependence of the far-infrared polarization fraction toward the OMC-1 star-forming region using observations from HAWC+/SOFIA at 53, 89, 154, and 214 μm. We find that the shape of the far-infrared polarization spectrum is variable across the cloud and that there is evidence of a correlation between the slope of the polarization spectrum and the average line-of-sight temperature. The slope of the polarization spectrum tends to be negative (falling toward longer wavelengths) in cooler regions and positive or flat in warmer regions. This is very similar to what was discovered in ρ Oph A via SOFIA polarimetry at 89 and 154 μm. Like the authors of this earlier work, we argue that the most natural explanation for our falling spectra is line-of-sight superposition of differing grain populations, with polarized emission from the warmer regions and less-polarized emission from the cooler ones. In contrast with the earlier work on ρ Oph A, we do not find a clear correlation of polarization spectrum slope with column density. This suggests that falling spectra are attributable to variations in grain alignment efficiency in a heterogeneous cloud consistent with radiative torques theory. Alternative explanations in which variations in grain alignment efficiency are caused by varying gas density rather than by varying radiation intensity are disfavored.
| Original language | English (US) |
|---|---|
| Article number | abd090 |
| Journal | Astrophysical Journal |
| Volume | 907 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 20 2021 |
Funding
This work is based on observations made with the NASA/ DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract NAS2-97001, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. Financial support for this work was provided by NASA through awards SOF 05-0038 and SOF 05-0018 issued by USRA to Villanova University and awards SOF 06-0116 and SOF 07-0147 issued by USRA to Northwestern University. Portions of this work were carried out at the Jet Propulsion Laboratory, operated by the California Institute of Technology under a contract with NASA. Parts of the analysis were performed using the Clusty Computing Facility in the Villanova University Department of Astrophysics and Planetary Science. We thank Andrej Prša for his support in leading and maintaining this resource. The authors would like to thank the anonymous referee for their very detailed and helpful comments. Facility: SOFIA (HAWC+).
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science