6 Summary

In this paper we present IRAS co-added images and large-scale CO(1-0), ¹³CO(1-0), and C¹⁸O(1-0) millimeter molecular line observations of the globular filaments GF 17 and GF 20 in the Lupus complex of dark clouds. The IRAS images have revealed that these clouds have extended emission at 60 and $100~\mu$m. We have used a simple uniform dust excitation model to derive opacities, color temperatures, and visual extinctions for the dust emitting at 60 and 100 $\mu$m. We derived gas column densities, have searched for correlations between gas and dust, and analysed the velocity structure of GF 17 and GF 20. We summarize our findings below:

$\bullet$ We find a good agreement between the $100~\mu$m optical depth images and the ¹³CO integrated emission maps. The dust opacity is well correlated with ¹³CO integrated intensity within the filamentary regions of GF 17 and GF 20. However, no correlation between these two quantities is found within the denser main core region of GF 17, probably due to saturation of the ¹³CO emission therein. Comparison of the $100~\mu$m optical depth with C¹⁸O integrated intensity in GF 17 and GF 20 indicates that the dust optical depth and the gas column density are well correlated.

$\bullet$ The variation of the dust color temperature with position in GF 17 and GF 20 clearly requires the presence of an external dust heating mechanism capable of penetrating these clouds to a reasonable depth. The best candidate for the external source heating the dust in GF 17 and GF 20 is the ISRF due to the nearby Sco OB2 association.

$\bullet$ We find a correlation between the measured dispersion in our extinction determinations and the extinction toward both clouds, which is very similar to that found for the L977 and IC 5146 clouds, and interpret this as evidence that the edges of GF 17 and GF 20 are characterized by a smooth density gradient.

$\bullet$ Analysis of the gas velocity structure within GF 17 and GF 20 reveals evidence for smooth large-scale streaming motions along the filamentary structures with magnitude ${\sim}0.5$ km s^-1 pc^-1. These velocity gradients cannot be interpreted easily as large-scale rotation or shear. Instead, we argue that the smooth velocity gradients observed over the full extents of GF 17 and GF 20 are the best evidence that the gas kinematics in these clouds is likely due to a propagating shock front. Both the dynamical time scales (a few million years) and the spatial orientation of these velocity gradients provide observational evidence for interactions of the GF 17 and GF 20 globular filaments with the Upper-Scorpius and Upper-Centaurus-Lupus HI expanding shells.

Acknowledgements

The authors would like to thank Dr. Dan Clemens for providing the co-added IRAS images, and the SEST operators Felipe McAuliffe and Francisco Azagra for assistance with the observations. This work has been partially supported by a grant from Fundação para a Ciência e Tecnologia (FCT, Portugal) to J.L.Y. Support from FCT to M.C.M. in the form of a scholarship is gratefully acknowledged.