An analysis of star formation with Herschel in the Hi-GAL Survey. II.
  The tips of the Galactic bar
  We present the physical and evolutionary properties of prestellar and
protostellar clumps in the Herschel Infrared GALactic plane survey (Hi-GAL) in
two large areas centered in the Galactic plane and covering the tips of the
long Galactic bar at the intersection with the spiral arms. The areas fall in
the longitude ranges 19 < l < 33 and 340 < l < 350, while latitude is -1 < b <
1. Newly formed high mass stars and prestellar objects are identified and their
properties derived and compared. A study is also presented on five giant
molecular complexes at the further edge of the bar. The star-formation rate was
estimated from the quantity of proto-stars expected to form during the collapse
of massive turbulent clumps into star clusters. This new method was developed
by applying a Monte Carlo procedure to an evolutionary model of turbulent cores
and takes into account the wide multiplicity of sources produced during the
collapse. The star-formation rate density values at the tips are 1.2 +- 0.3
10-3 Msol/yr/kpc2 and 1.5+-0.3 10-3 Msol/yr/kpc2 in the first and fourth
quadrant, respectively. The same values estimated on the entire field of view,
that is including the tips of the bar and background and foreground regions,
are 0.9+-0.2 10-3 Msol/yr/kpc2 and 0.8+-0.2 10-3 Msol/yr/kpc2. The conversion
efficiency is approximately 0.8% in the first quadrant and 0.5% in the fourth
quadrant, and does not show a significant difference in proximity of the bar.
The star forming regions identified through CO contours at the further edge of
the bar show star-formation rate densities larger than the surrounding regions
but their conversion efficiencies are comparable. Our results suggest that the
star-formation activity at the bar is due to a large amount of dust and
molecular material rather than being due to a triggering process.
