A study of the kinematics of the local dark clouds |
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| Authors: | B Ramesh |
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| Institution: | (1) Raman Research Institute, C. V. Raman Avenue, Sadashivanagar, 560 080 Bangalore |
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| Abstract: | Lack of reliable estimates of distances to most of the local dark clouds has, so far, prevented a quantitative study of their
kinematics. Using a statistical approach, we have been able to extract the average spatial distribution as well as the kinematical
behaviour of the local dark clouds from their measured radial velocities. For this purpose, we have obtained radial velocities
for 115 southern clouds and used the data from the literature for the northern ones. In this paper we present this new data,
analyse the combined data and compare our results with those arrived at by earlier studies.
The local clouds are found to be expanding at a speed of ∼ 4 kms-1 which is in general agreement with the estimates from optical and HI studies. However, it is found that the kinematics of
the local clouds is not described by the model proposed for the local HI gas where a ring of gas expanding from a point gets
sheared by the galactic rotation. Rather, the observed distribution of their radial velocities is best understood in terms
of a model in which the local clouds are participating in circular rotation appropriate to their present positions with a
small expansion also superimposed. This possibly implies that cloud-cloud collisions are important. The spatial distribution
of clouds derived using such a model is in good agreement with the local dust distribution obtained from measurements of reddening
and extinction towards nearby stars. In particular, a region of size ∼ 350 pc in diameter enclosing the Sun is found to be
devoid of clouds. Intriguingly, most clouds in the longitude range 100‡ to 145‡ appear to have negative radial velocities
implying that they are approaching us.
Carried out under the auspices of the Joint Astronomy Program, Department of Physics, Indian Institute of Science, Bangalore
in partial fulfillment of the requirements for the Degree of Doctor of Philosophy. |
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| Keywords: | Local ISM structure Gould’ s belt dispersion in cloud velocities |
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