The OH ground-state masers in W3(OH) - II. Polarization and multifrequency results

Abstract

We present observational data on OH masers in W3(OH) with the emphasis on the three ground-state lines, other than 1665 MHz, and on the polarization of the masers. Polarization studies indicate that the magnetic field orientation varies systematically over the field of view, and the large number of Zeeman pairs detected has allowed us to construct a map of the magnetic field in the source. In several parts of the region, the masers lie in arcs where the major axis of the maser usually lies parallel to the arc; these may delineate propagating shocks. A spectacular arc of maser emission occurs in the far south of the region at both 1665 and 1667 MHz. Such co-propagation of maser frequencies is very rare and exists only for pairs of lines where one line is 1665 MHz.