Gas and dust emission in the Lupus globular filaments GF 17 and GF 20

Abstract

We present large-scale millimeter molecular line observations as well as IRAS co-added images of the globular filaments GF 17 and GF 20 in the southern constellation of Lupus. A comparison is made of the extended far-infrared emission detected by IRAS at 60 and 100 μ m and the CO($1{-}0$), 13 CO($1{-}0$), and C 18 O($1{-}0$) emission in GF 17 and GF 20. Based on the far-infrared emission estimates of the dust temperature, optical depth and visual extinction are derived. We find a correlation between the measured dispersion in our extinction determinations and the extinction toward the clouds, which is very similar to that found for other clouds, and interpret this as evidence that the cloud edges are characterized by a smooth density gradient. We find a remarkably good agreement between our $100~\mu$m optical depth images and the 13 CO integrated emission maps. The dust $100~\mu$m optical depth is well correlated with the gas column density suggesting that the far-infrared emission must originate from a substantial depth in the clouds. The dust temperature is found to be anticorrelated with the gas column density indicating that these clouds are heated externally. Our calculated far-infrared luminosities of GF 17 and GF 20 imply that the dominant source of dust heating is the ISRF due to the nearby Sco OB2 association. 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 . Our results indicate that the velocity gradients are likely due to the interaction of GF 17 and GF 20 with the Upper-Scorpius and Upper-Centaurus-Lupus HI expanding shells, via propagating shock fronts.