Kinematics of the Ursa Major Molecular Clouds
M. W. Pound, A. A. Goodman;
ApJ, 1997, 482, 334
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 the 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 and 25 mu m emission.
We find an offset of up to 4 km s-1
between the centroid velocities of the CO and H I, a large-scale velocity
gradient in the gas of ~0.3 km s-1 pc-1, 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 less organized.
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 toward the Galactic plane.
This model adequately
accounts for the atomic-molecular velocity offset, the velocity gradients,
the line width gradient, and the IRAS colors.
KEYWORDS: ism: clouds, ism: individual name: ursa major, ism: kinematics and dynamics, radio lines: ism
PERSOKEY:ursa major, co, h2, cirrus, ,
CODE: pound97