Squeezed between shells? On the origin of the Lupus I molecular cloud. -
  II. APEX CO and GASS HI observations
  [Abridged] The Lupus I cloud is found between the Upper-Scorpius and the
Upper-Centaurus-Lupus sub-groups, where the expanding USco HI shell appears to
interact with a bubble currently driven by the winds of the remaining B-stars
of UCL. We investigate if the Lupus I molecular could have formed in a
colliding flow, and how the kinematics of the cloud might have been influenced
by the larger scale gas dynamics. We performed APEX 13CO and C18O observations
of three parts of Lupus. We compare these results to the atomic hydrogen data
from the GASS HI survey and our dust emission results presented in the previous
paper. Based on the velocity information, we present a geometric model for the
interaction zone between the USco shell and the UCL wind bubble. We present
evidence that the molecular gas of Lupus I is tightly linked to the atomic
material of the USco shell. The CO emission in Lupus I is found mainly at
velocities in the same range as the HI velocities. Thus, the molecular cloud is
co-moving with the expanding USco atomic Hi shell. The gas in the cloud shows a
complex kinematic structure with several line-of-sight components that overlay
each other. The non-thermal velocity dispersion is in the transonic regime in
all parts of the cloud and could be injected by external compression. Our
observations and the derived geometric model agree with a scenario where Lupus
I is located in the interaction zone between the USco shell and the UCL wind
bubble. The kinematics observations are consistent with a scenario where the
Lupus I cloud formed via shell instabilities. The particular location of Lupus
I between USco and UCL suggests that counter-pressure from the UCL wind bubble
and pre-existing density enhancements, perhaps left over from the gas stream
that formed the stellar subgroups, may have played a role in its formation.
