Physical characterization of S169: A prototypical IR bubble associated
  with the massive star-forming region IRAS12326-6245
  With the aim of studying the properties of Galactic IR bubbles and their
impact in massive star formation, we present a study of the IR bubble S169,
associated with the massive star forming region IRAS12326-6245. We used
CO(2-1),$^{13}$CO(2-1), C$^{18}$O(2-1), HCN(3-2), and HCO+(3-2) line data
obtained with the APEX telescope to study the properties of the molecular gas
in the nebula and the IRAS source . To analyze the properties and distribution
of the dust, we used IRAC-GLIMPSE, Herschel, and ATLASGAL data. The properties
of the ionized gas were studied using images obtained from the SUMSS survey and
SuperCOSMOS database. In our search for stellar and protostellar objects in the
region, we used IR and optical point source calalogs. The new APEX observations
allowed us to identify three molecular components associated with the nebula,
namely: at $-$39 km/s (component A), $-$25 km/s (component B), and $-$17 km/s
(component C). Six molecular condensations (MC1 to MC6) were identified in
component A, with MC3 (the densest and more massive one) being the molecular
counterpart of IRAS12326-6245. For this source, we estimated an H$_2$ column
density up to 8$\times$10$^{23}$ cm$^{-2}$. To explain the morphology and
velocity of components A, B, and C, we propose a simple model consisting of a
partially complete semisphere-like structure expanding at ~ 12 km/s. The
introduction of this model has led to a discussion about the distance to both
S169 and IRAS12326-6245, which was estimated to be ~ 2 kpc. Several candidate
YSOs were identified, projected mostly onto the molecular condensations MC3,
MC4, and MC5, which indicates that the star-formation process is very active at
the borders of the nebula. A comparison between observable and modeled
parameters was not enough to discern whether the collect-and-collapse mechanism
is acting at the edge of S169.
