An Arecibo Survey for Zeeman Splitting in OH Megamaser Galaxies

TL;DR

This survey using the Arecibo Observatory detected Zeeman splitting in OH megamasers, revealing magnetic fields that are likely dynamically significant, with new detections expanding understanding of magnetic influence in extragalactic maser regions.

Contribution

First comprehensive Arecibo survey detecting Zeeman splitting in OH megamasers, identifying new magnetic field measurements and suggesting their dynamic importance.

Findings

Magnetic fields in OHMs range from 6.1 to 27.6 mG.

Most detected magnetic fields are larger than in Galactic OH masers.

Magnetic fields likely play a significant role in OH masing clouds.

Abstract

We present the results of a comprehensive survey using the Arecibo Observatory for Zeeman splitting of OH lines in OH megamasers (OHMs). A total of seventy-seven sources were observed with the Arecibo telescope. Of these, maser emission could not be detected for eight sources, and two sources were only ambiguously detected. Another twenty-seven sources were detected at low signal-to-noise ratios or with interference that prevented placing any useful limits on the presence of magnetic fields. In twenty-six sources, it was possible to place upper limits on the magnitude of magnetic fields, typically between 10-30 mG. For fourteen sources, the Stokes V spectra exhibit features consistent with Zeeman splitting. Eleven of these fourteen are new detections, and the remaining three are re-detections of Stokes V detections in Robishaw et al. (2008). Among confident new detections, we derive magnetic fields associated with maser regions with magnitudes ranging from 6.1-27.6 mG. The distribution of magnetic field strengths suggests the magnetic fields in OH masing clouds in OHMs are larger than those in Galactic OH masers. The results are consistent with magnetic fields playing a dynamically important role in OH masing clouds in OHMs.