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Carbon monoxide line emission from clumpy molecular clouds: The case of Orion
Abstract
It is generally believed that molecular clouds are clumpy. In clumpy molecular clouds the large scale spatial distribution of the emission from the ionized, neutral, and molecular carbon species is significantly different than it would be in a cloud with a smooth density distribution. Thus it should be possible to derive some general properties of the clumps (i.e. size, volume filling factor, kinematics, etc.) by observing these species, even if individual clumps are not spatially resolved. We have built a receiver capable of observing both the J = 3 $\to$ 2 transition of $\sp{12}$CO and $\sp{13}$CO and the $\sp3$P$\sb1$ $\to$ $\sp3$P$\sb0$ transition of neutral atomic carbon, and a filterbank of novel design that acts as its backend. We have used this instrument to obtain a map of $\sp{12}$CO J = 3 $\to$ 2 in the Orion A region. The observed line shapes, and a comparison of the intensity of this line to that of the J = 1 $\to$ 0 transition, strongly suggests that this region is clumpy, that a kinetic temperature gradient exists within each clump, and that the source of the heating is situated on the surface of the cloud. Furthermore, an analysis of the smoothness of very high signal-to-noise $\sp{12}$CO and $\sp{13}$CO J = 1 $\to$ 0 spectra in the region indicates that the volume filling factor of the clumps increases from the surface to the core of the cloud. We develop a model of an edge-heated clumpy molecular cloud that takes into account the chemical and thermal effects of the UV photons on the density and temperature structure of the clumps. We show that this model can reproduce the observed $\sp{12}$CO intensities and line ratios in the region, and is in qualitative agreement with other characteristic features observed in this and other similar regions (i.e. widespread presence of warm CO, of neutral carbon, and of high dipole moment species). We discuss the implications of these results on the general properties of the clumps in the Orion region.
Subject Area
Physics|Electrical engineering|Astrophysics
Recommended Citation
Tauber, Jan Alejandro, "Carbon monoxide line emission from clumpy molecular clouds: The case of Orion" (1990). Doctoral Dissertations Available from Proquest. AAI9022750.
https://scholarworks.umass.edu/dissertations/AAI9022750