Searching for Inflow Towards Massive Starless Clump Candidates
  Identified in the Bolocam Galactic Plane Survey
  Recent Galactic plane surveys of dust continuum emission at long wavelengths
have identified a population of dense, massive clumps with no evidence for
on-going star formation. These massive starless clump candidates are excellent
sites to search for the initial phases of massive star formation before the
feedback from massive star formation effects the clump. In this study, we
search for the spectroscopic signature of inflowing gas toward starless clumps,
some of which are massive enough to form a massive star. We observed 101
starless clump candidates identified in the Bolocam Galactic Plane Survey
(BGPS) in HCO+ J = 1-0 using the 12m Arizona Radio Observatory telescope. We
find a small blue excess of E = (Nblue - Nred)/Ntotal = 0.03 for the complete
survey. We identified 6 clumps that are good candidates for inflow motion and
used a radiative transfer model to calculate mass inflow rates that range from
500 - 2000 M /Myr. If the observed line profiles are indeed due to large-scale
inflow motions, then these clumps will typically double their mass on a free
fall time. Our survey finds that massive BGPS starless clump candidates with
inflow signatures in HCO+ J = 1-0 are rare throughout our Galaxy.
