High-Resolution Observations of H i Zeeman Absorption toward DR 21

Details High-Resolution Observations of H i Zeeman Absorption toward DR 21 High-Resolution Observations of H i Zeeman Absorption toward DR 21

Feb 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...476..209r&link_type=abstract

Astrophysical Journal v.476, p.209

Astronomy and Astrophysics

Astronomy

15

Ism: H Ii Regions, Ism: Individual Alphanumeric: Dr 21, Ism: Kinematics And Dynamics, Ism: Magnetic Fields, Infrared: Ism: Lines And Bands, Radio Lines: Ism

Scientific paper

DR 21 has been imaged in H I at high resolution (~5") in both l( and right circular polarization with the VLA. The continuum emission is nearly totally absorbed with opacities > 5 over about 20 km s-1; the FWHM line width is unusually large (~35 km s-1). At least three components are present: two narrow ones at VLSR = -5 km s-1 and +10 km s-1 and a negative-velocity wing whose opacity can be measured out to VLSR = -30 km s-1 in some places. No positive-velocity wing is detected. The midpoint of the negative-velocity wing varies between -25 and -10 km s-1, and the full extent is typically >~20 km s-1. The wing is detected over most of the H II region core except in the very southwest corner, near H II region C and in the northern region around H II region D. The opacity in the wing is ~0.5 toward the eastern diffuse continuum emission and rises to ~2 toward the H II core. This negative-velocity H I 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 H II region with lower negative velocities near the edge of the tube. The H I gas appears to be accelerating away from the southwest of the core, from a position close to H II 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 DR 21 compact H II region core. No magnetic field (|B| < 50 mu G) is detected in the narrow-line component at VLSR = +10 km s-1; a strong magnetic field of a few hundred microgauss is observed at a position near the H II core in the H I gas at negative velocities.

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