Non-Zeeman circular polarization of CO rotational lines in SNR IC 443
Abstract
Context. We study interstellar magnetic fields by measuring the polarization in molecular spectral lines and thermal emission of dust. Aims. We report detection of non-Zeeman circular polarization and linear polarization levels of up to 1% in the ^(12)CO spectral line emission in a shocked molecular clump around the supernova remnant (SNR) IC 443. We examine our polarization results to confirm that the circular polarization signal in CO lines is caused by a conversion of linear to circular polarization, consistent with anisotropic resonant scattering. In this process background, linearly polarized CO emission interacts with similar foreground molecules aligned with the ambient magnetic field and scatters at a transition frequency. The difference in phase shift between the orthogonally polarized components of this scattered emission can cause a transformation of linear to circular polarization. Methods. We compared linear polarization maps from the dust continuum, which were obtained with PolKa at APEX, and ^(12)CO (J = 2 → 1) and (J = 1 → 0) from the IRAM 30-m telescope. We found no consistency between the two sets of polarization maps. We then reinserted the measured circular polarization signal in the CO lines across the source to the corresponding linear polarization signal to test whether the linear polarization vectors of the CO maps were aligned with those of the dust before this linear to circular polarization conversion. Results. After the flux correction for the two transitions of the CO spectral lines, the new polarization vectors for both CO transitions aligned with the dust polarization vectors, establishing that the non-Zeeman CO circular polarization is due to a linear to circular polarization conversion.
Additional Information
© 2013 ESO. Article published by EDP Sciences. Received 15 May 2013. Accepted 8 August 2013. Published online 01 October 2013. The authors are grateful to C. Thum for very helpful and constructive comments and discussion. T. Hezareh's research was funded by the Alexander von Humboldt foundation. M. Houde's research is funded through the NSERC Discovery Grant, Canada Research Chair, Canada Foundation for Innovation, and Western's Academic Development Fund programs. A. Gusdorf acknowledges support by the grant ANR-09-BLAN-0231-01 from the French Agence Nationale de la Recherche as part of the SCHISM project.Attached Files
Published - aa21900-13.pdf
Submitted - 1308.3683v1.pdf
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Additional details
- Eprint ID
- 43269
- Resolver ID
- CaltechAUTHORS:20140108-130917649
- Alexander von Humboldt foundation
- NSERC Discovery Grant
- Canada Research Chair
- Canada Foundation for Innovation
- Western's Academic Development Fund programs
- ANR-09-BLAN-0231-01
- Agence Nationale de la Recherche (ANR) SCHISM Project
- Created
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2014-01-08Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field