A New Optical Polarization Catalog for the Small Magellanic Cloud: The Magnetic Field Structure
Abstract
We present a new optical polarimetric catalog for the Small Magellanic Cloud (SMC). It contains a total of 7207 stars, located in the northeast (NE) and Wing sections of the SMC and part of the Magellanic Bridge. This new catalog is a significant improvement compared to previous polarimetric catalogs for the SMC. We used it to study the sky-projected interstellar magnetic field structure of the SMC. Three trends were observed for the ordered magnetic field direction at position angles (PAs) of (65° ± 10°), (115° ± 10°), and (150° ± 10°). Our results suggest the existence of an ordered magnetic field aligned with the Magellanic Bridge direction and SMC’s Bar in the NE region, which have PAs roughly at 115.°4 and 45°, respectively. However, the overall magnetic field structure is fairly complex. The trends at 115° and 150° may be correlated with the SMC’s bimodal structure, observed in Cepheids’ distances and HI velocities. We derived a value of {{B}sky}=(0.947+/- 0.079) μG for the ordered sky-projected magnetic field, and δ B=(1.465+/- 0.069) μG for the turbulent magnetic field. This estimate of {{B}sky} is significantly larger (by a factor of ∼10) than the line of sight field derived from Faraday rotation observations, suggesting that most of the ordered field component is on the plane of the sky. A turbulent magnetic field stronger than the ordered field agrees with observed estimates for other irregular and spiral galaxies. For the SMC the {{B}sky}/δ B ratio is closer to what is observed for our Galaxy than other irregular dwarf galaxies.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2015
- DOI:
- 10.1088/0004-637X/806/1/94
- arXiv:
- arXiv:1504.02104
- Bibcode:
- 2015ApJ...806...94L
- Keywords:
-
- galaxies: ISM;
- Magellanic Clouds;
- magnetic fields;
- techniques: polarimetric;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Updated to match published version (includes extra online figures)