VLA H i and OH Zeeman Observations toward M17

Abstract

We have carried out high-resolution (D26A) VLA H I Zeeman and main-line OH Zeeman obser- vations toward M17. The morphology of the 26A resolution H I line-of-sight magnetic Ðeld strength (B ) images show general agreement with those presented in Paper I with D60A resolution. The similarities los include the rise of the 20 km s~1 B toward the H II region/M17 SW interface and the concentration of high 11È17 km s~1 B los to the northwest. However, the D26A H I B los stronger than those measured with D60A resolution, suggesting that there is small-scale structure in the los reported here are up to 2 times M17 SW magnetic Ðeld. H I B values as high as D[750 kG are detected toward the M17 H II region/ M17 SW interface region at 20 km s~1. OH 1665 MHz Zeeman detections (with D22A resolution) los B were also made toward Ðve D1@ regions along the M17 H II region/M17 SW interface. The average los line-of-sight magnetic Ðeld strength (B ) in the three northern OH detection regions is D]250 kG. Another of the OH condensations is positionally and kinematically coincident with the region of high H los I B Zeeman detections presented here support the Ðndings of Paper I, which indicated that the M17 SW los detected toward the M17 SW interface at 20 km s~1 and has similar B .The higher resolution H I B los molecular los cloud core is magnetically supercritical and subvirial, but is in approximate dynamic equi- librium as a whole. Assuming that the northern OH condensations are self-gravitating, we Ðnd that the critical magnetic Ðeld strength (B than the average observed B value. Our estimates also show that even including support from the S,crit ) needed to provide total support against gravity is D3 times higher magnetic wave energy (assumed equal to that of the nonthermal motions), these northern OH conden- los sations cannot support themselves against gravitational collapse.