VLA H I and OH Zeeman Observations toward M17

Details VLA H I and OH Zeeman Observations toward M17 VLA H I and OH Zeeman Observations toward M17

Oct 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...560..821b&link_type=abstract

The Astrophysical Journal, Volume 560, Issue 2, pp. 821-840.

Astronomy and Astrophysics

Astronomy

42

Ism: H Ii Regions, Ism: Clouds, Ism: Individual: Messier Number: M17, Ism: Magnetic Fields, Radio Lines: Ism

Scientific paper

We have carried out high-resolution (~26") VLA H I Zeeman and main-line OH Zeeman observations toward M17. The morphology of the 26" resolution H I line-of-sight magnetic field strength (Blos) images show general agreement with those presented in Paper I with ~60" resolution. The similarities include the rise of the 20 km s-1 Blos toward the H II region/M17 SW interface and the concentration of high 11-17 km s-1 Blos to the northwest. However, the ~26" H I Blos reported here are up to 2 times stronger than those measured with ~60" resolution, suggesting that there is small-scale structure in the M17 SW magnetic field. H I Blos values as high as ~-750 μG are detected toward the M17 H II region/M17 SW interface region at 20 km s-1. OH 1665 MHz Blos Zeeman detections (with ~22" resolution) were also made toward five ~1' regions along the M17 H II region/M17 SW interface. The average line-of-sight magnetic field strength (Blos) in the three northern OH detection regions is ~+250 μG. Another of the OH condensations is positionally and kinematically coincident with the region of high H I Blos detected toward the M17 SW interface at 20 km s-1 and has similar Blos.The higher resolution H I Zeeman Blos detections presented here support the findings of Paper I, which indicated that the M17 SW molecular cloud core is magnetically supercritical and subvirial, but is in approximate dynamic equilibrium as a whole. Assuming that the northern OH condensations are self-gravitating, we find that the critical magnetic field strength (BS,crit) needed to provide total support against gravity is ~3 times higher than the average observed Blos value. Our estimates also show that even including support from the magnetic wave energy (assumed equal to that of the nonthermal motions), these northern OH condensations cannot support themselves against gravitational collapse.

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