NCSA Astronomy Digital Image Library
Project Abstract and Description
Kinematics of the Ursa Major Molecular Clouds
M. Pound and A. Goodman
Contact: Marc Pound
Email: pound@teddi.berkeley.edu
Number of images in project: 7
References: 1996BAAS..188.4203P
Abstract
We present a kinematic analysis of the atomic and molecular gas in
the Ursa Major molecular clouds. The analysis is based on a new CO survey of
the complex made with linear resolution of 0.05 pc and existing H I
observations.
The clouds lie in projection on an expanding shell of material known as the
North Celestial Pole loop. The molecular structure of complex is dominated by
several long (> 5 pc) filaments, some of which are both extremely straight
and extremely narrow (< 0.2 pc across). These filaments are enclosed in a
sheath of neutral atomic hydrogen that has a kinematic signature distinct from
the surrounding atomic gas. The tips of the filaments are regions of enhanced
IRAS 12 micron and 25 micron emission. We find an offset of up to 4
km/s between the centroid velocities of the CO and H I, a large-scale velocity
gradient in the gas of 0.3 km/s/pc, and a similar large-scale
gradient in the H I line width. The CO velocity field follows a trend similar
to the H I, but is much more chaotic. A weak line width gradient in the CO may
also be present.
We present a model in which the clouds lie near the surface of the expanding
bubble and, after having interacted with the bubble's wind, are now slowly
``sliding'' down the bubble towards the Galactic plane. This model adequately
accounts for the atomic-molecular velocity offset, the velocity gradients, the
line width gradient, and the IRAS colors.
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