Squeezed between shells? On the origin of the Lupus I molecular cloud.
  APEX/LABOCA, Herschel, and Planck observations
  The Lupus I cloud is found between the Upper-Scorpius (USco) and the
Upper-Centaurus-Lupus (UCL) sub-groups of the Sco-Cen OB-association, where the
expanding USco H I shell appears to interact with a bubble currently driven by
the winds of the remaining B-stars of UCL.We want to study how collisions of
large-scale interstellar gas flows form and influence new dense clouds in the
ISM.We performed LABOCA continuum sub-mm observations of Lupus I that provide
for the first time a direct view of the densest, coldest cloud clumps and cores
at high angular resolution.We complemented those by Herschel and Planck data
from which we constructed column density and temperature maps.We calculated
PDFs to characterize the density structure of the cloud.The northern part of
Lupus I is found to have on average lower densities and higher temperatures as
well as no active star formation.The center-south part harbors dozens of
pre-stellar cores where density and temperature reach their maximum and
minimum, respectively.Our analysis of the column density PDFs from the Herschel
data show double peak profiles for all parts of the cloud which we attribute to
an external compression.In those parts with active star formation, the PDF
shows a power-law tail at high densities.The PDFs we calculated from our LABOCA
data trace the denser parts of the cloud showing one peak and a power-law
tail.With LABOCA we find 15 cores with masses between 0.07 and 1.71 Msun and a
total mass of ~8 Msun.The total gas and dust mass of the cloud is ~164 Msun and
hence 5% of the mass is in cores.From the Herschel and Planck data we find a
total mass of ~174 Msun and ~171 Msun, respectively.The position, orientation
and elongated shape of Lupus I, the double peak PDFs and the population of
pre-stellar and protostellar cores could be explained by the large-scale
compression from the advancing USco H I shell and the UCL wind bubble.
