The Far-infrared Polarization Spectrum of ρ Ophiuchi A from HAWC+/SOFIA Observations

Fabio P. Santos, David T. Chuss, C. Darren Dowell, Martin Houde, Leslie W. Looney, Enrique Lopez Rodriguez, Giles Novak, Derek Ward-Thompson, Marc Berthoud, Daniel A. Dale, Jordan A. Guerra, Ryan T. Hamilton, Shaul Hanany, Doyal A. Harper, Thomas K. Henning, Terry Jay Jones, Alex Lazarian, Joseph M. Michail, Mark R. Morris, Johannes StaguhnIan W. Stephens, Konstantinos Tassis, Christopher Q. Trinh, Eric Van Camp, C. G. Volpert, Edward J. Wollack

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


We report on polarimetric maps made with HAWC+/SOFIA toward ρ Oph A, the densest portion of the ρ Ophiuchi molecular complex. We employed HAWC+ bands C (89 μm) and D (154 μm). The slope of the polarization spectrum was investigated by defining the quantity , where p C and p D represent polarization degrees in bands C and D, respectively. We find a clear correlation between and the molecular hydrogen column density across the cloud. A positive slope ( > 1) dominates the lower-density and well-illuminated portions of the cloud, which are heated by the high-mass star Oph S1, whereas a transition to a negative slope ( < 1) is observed toward the denser and less evenly illuminated cloud core. We interpret the trends as due to a combination of (1) warm grains at the cloud outskirts, which are efficiently aligned by the abundant exposure to radiation from Oph S1, as proposed in the radiative torques theory; and (2) cold grains deep in the cloud core, which are poorly aligned owing to shielding from external radiation. To assess this interpretation, we developed a very simple toy model using a spherically symmetric cloud core based on Herschel data and verified that the predicted variation of is consistent with the observations. This result introduces a new method that can be used to probe the grain alignment efficiency in molecular clouds, based on the analysis of trends in the far-infrared polarization spectrum.

Original languageEnglish (US)
Article number113
JournalAstrophysical Journal
Issue number2
StatePublished - Sep 10 2019

Bibliographical note

Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved..


  • Dust
  • Extinction-ism: Magnetic fields-ism: Individual objects (rho ophiuchi molecular cloud)-techniques: Polarimetric


Dive into the research topics of 'The Far-infrared Polarization Spectrum of ρ Ophiuchi A from HAWC+/SOFIA Observations'. Together they form a unique fingerprint.

Cite this