We present the first interferometric polarization map of the W3 ( OH ) massive star-forming region observed with the Submillimeter Array ( SMA ) at 878 \mu \mathrm { m } with an angular resolution of 1 \farcs 5 ( about 3 \times 10 ^ { 3 } \mathrm { AU } ) .
Polarization is detected in the W3 ( H _ { 2 } O ) hot core , an extended emission structure in the north-west of W3 ( H _ { 2 } O ) , and part of the W3 ( OH ) ultracompact H ii region .
The W3 ( H _ { 2 } O ) hot core is known to be associated with a synchrotron jet along the east-west direction .
In this core , the inferred magnetic field orientation is well aligned with the synchrotron jet and close to the plane of sky .
Using the Chandrasekhar-Fermi method with the observed dispersion in polarization angle , we estimate a plane-of-sky magnetic field strength of 17.0 \mathrm { mG } .
Combined with water maser Zeeman measurements , the total magnetic field strength is estimated to be 17.1 \mathrm { mG } , comparable to the field strength estimated from the synchrotron model .
The magnetic field energy dominates over turbulence in this core .
In addition , the depolarization effect is discerned in both SMA and JCMT measurements .
Despite the great difference in angular resolutions and map extents , the polarization percentage shows a similar power-law dependence with the beam averaged column density .
We suggest that the column density may be an important factor to consider when interpreting the depolarization effect .