Excited-state hydroxyl maser polarimetry: Who ate all the {\pi}s?

• Published in: arXiv.org
• Main Authors: Green, James A, Caswell, James L, McClure-Griffiths, Naomi M
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 27.04.2015
• Subjects: Broadband; Emission; Faraday effect; Low level; Masers; Methanol; Physics - Astrophysics of Galaxies; Polarimetry; Polarization; Star & galaxy formation; Star formation
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1504.07062

We present polarimetric maser observations with the Australia Telescope Compact Array (ATCA) of excited-state hydroxyl (OH) masers. We observed 30 fields of OH masers in full Stokes polarization with the Compact Array Broadband Backend (CABB) at both the 6030 and 6035 MHz excited-state OH transitions, and the 6668-MHz methanol maser transition, detecting 70 sites of maser emission. Amongst the OH we found 112 Zeeman pairs, of which 18 exhibited candidate {\pi} components. This is the largest single full polarimetric study of multiple sites of star formation for these frequencies, and the rate of 16% {\pi} components clearly indicates the {\pi} component exists, and is comparable to the percentage recently found for ground-state transitions. This significant percentage of {\pi} components, with consistent proportions at both ground- and excited-state transitions, argues against Faraday rotation suppressing the {\pi} component emission. Our simultaneous observations of methanol found the expected low level of polarisation, with no circular detected, and linear only found at the less than or equal to 10% level for the brightest sources.