Linear Polarization Observations of Water Masers in W3 IRS 5

Abstract

We present a magnetic field mapping of water maser clouds in the star-forming region W3 IRS 5, which has been made on the basis of the linear polarization VLBI observation. Using the Very Long Baseline Array at 22.2 GHz, 16 of 61 detected water masers were found to be linearly polarized with polarization degrees up to 13%. Although 10 polarized features were widely distributed in the whole W3 IRS 5 water maser region, they had position angles similar to the magnetic field vectors (~75° east from the north). The magnetic field vectors are roughly perpendicular to the spatial alignments of the maser features. They are consistent with the hourglass model of the magnetic field, which was previously proposed to explain the magnetic field in the whole W3 Main region (r ~ 0.1 pc). They are, on the other hand, not aligned to the directions of maser feature proper motions observed previously. This implies that the W3 IRS 5 magnetic field was controlled by a collapse of the W3 Main molecular cloud rather than by the outflow originated from W3 IRS 5.