Phosphorus-bearing molecules in massive dense cores
  Phosphorus is a crucial element for the development of life, but so far
P-bearing molecules have been detected only in a few astrophysical objects,
hence its interstellar chemistry is almost totally unknown. Here we show new
detections of phosphorus nitride in a sample of dense cores in different
evolutionary stages of the intermediate- and high-mass star formation process:
starless, with protostellar objects, and with ultracompact HII regions. All
detected PN line widths are smaller than ~5 km/s , and they arise from regions
associated with kinetic temperatures smaller than 100 K. Because the few
previous detections reported in the literature are associated with warmer and
more turbulent sources, the results of this work show that PN can arise from
relatively quiescent and cold gas. This information is challenging for
theoretical models that invoke either high desorption temperatures or grain
sputtering from shocks to release phosphorus into the gas phase. Derived column
densities are of the order of 10^{11-12} cm^{-2}, marginally lower than the
values derived in the few high-mass star forming regions detected so far. New
constraints on the column density upper limit of phosphorus monoxide, the
fundamental unit of biologically relevant molecules, are also given.
