High Resolution HI Zeeman Absorption Observations of DR21

Details High Resolution HI Zeeman Absorption Observations of DR21 High Resolution HI Zeeman Absorption Observations of DR21

Feb 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996adil...dr...01r&link_type=abstract

NCSA Astronomy Digital Image Library

Astronomy and Astrophysics

Astronomy

Scientific paper

DR21 has been imaged in HI at high resolution (about 5 arcsec) in both left and right circular polarization with the VLA. The continuum emission is nearly totally absorbed with opacities greater than 5 over about 20 km/s; the line is unusually wide with FWHM about 35 km/s. At least three components are present: two narrow ones at LSR velocity = --5 km/s and 10 km/s and a negative-velocity wing whose opacity can be measured out to an LSR velocity = --30 km/s in some places. No positive velocity wing is detected. The midpoint of the negative-velocity wing varies between --25 and --10 km/s with a typical FWHM of about 20 km/s. The wing is detected over most of the HII region core except in the very southwest corner and in the northern region around HII region D. The opacity in the wing is about 0.5 toward the eastern diffuse continuum emission and rises to about 2 toward the HII core. This negative-velocity HI absorption is probably associated with the high-velocity outflow seen in CO. The velocity field of this outflow gas shows a high negative velocity tube through the center of the HII region with lower velocities near the edge of the tube. The HI gas appears to be accelerating from the above-mentioned southwest position, close to HII region C. This location for the origin of the outflow is consistent with that inferred from the CO observations. Zeeman measurements were made toward the DR21 compact HII region core. No magnetic field (B less than 50 microgauss) is detected in the narrow line component at an LSR velocity = 10 km/s; a strong magnetic field of a few hundred microgauss is observed at a position near the HII core in the HI gas at negative velocities.

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