| dc.description.abstract | Submillimetre molecular line observations of molecular clouds in
our galaxy are presented, and the data analysed using various alternative
cloud models.
A critical review is given of the methods commonly used to
interpret molecular line data, including both theoretical considerations
and issues relating to calibration and comparability of results
obtained with different telescopes. A detailed comparison is made
between results predicted from large velocity gradient (LVG) models,
including the generalisation to non-monotonic velocity flows, and
those given by "microturbulent" clouds.
An LVG model is employed in an investigation of conditions in the
molecular outflows frequently found in star formation regions, for
which observations in the CO J=3-2 rotational transition at 345 GHz
are presented. These are combined with lower frequency data from the
literature to derive various properties of the outflows for a sample
of 13 sources. The most important result is that local H2 densities
exist in the outflows which are higher, typically by an order of magnitude,
than previously derived average values obtained using only
lower frequency data.
Observations are presented of the S255 and DR21 clouds in the
transitions CO J=2-1, CO J=3-2, CS J=7-6, HCN J=4-3, HCO+ J=4-3 and
-3-
H13CO+ J=4-3 and are supplemented by continuum data at 350 s. n and
(for DR21) at 20 pm. It is shown that, although some features
of the data can be understood in terms of an LVG model, there is compelling
evidence for fragmentation of the clouds on length scales
much smaller than the cloud sizes. The data are used to constrain
the local H2 densities and relative molecular abundances in the
clumpy cloud cores, and compared with lower frequency results from
the literature.
The implications of these results for the star formation environment
are discussed, and an assessment made of possible strategies
for their further investigation. | en_US |
