Linear Polarization Observations of Water Masers in W3 IRS 5

We present a magnetic field mapping of water maser clouds in the star-formingregion W3 IRS5, which has been made on the basis of the linear polarizationVLBI observation. Using the Very Long Baseline Array (VLBA) at 22.2 GHz, 16 of61 detected water masers were found to be linearly polarized with polarizationdegrees up to 13%. Although 10 polarized features were widely distributed inthe whole W3 IRS5 water maser region, they had similar position angles of themagnetic field vectors (~75 deg from the north). The magnetic field vectors areroughly perpendicular to the spatial alignments of the maser features. They areconsistent with the hourglass model of the magnetic field, which was previouslyproposed 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 featureproper motions observed previously. This implies that the W3 IRS5 magneticfield was controlled by a collapse of the W3 Main molecular cloud rather thanthe outflow originated from W3 IRS5.Comment: 19 pages, 5 files, 1 table, accepted for publication in the Astrophysical Journal vol. 595, No.1 (2003 September 20 issue