In Search of Infall Motion in Molecular Clumps. IV. Mapping of the Global Infall Sources

Abstract

We have used the IRAM 30-m telescope to map some targets with HCO${}^{+}$ (1-0) and H${}^{13}$CO${}^{+}$ (1-0) lines in order to search for gas infall evidence in the clumps. In this paper, we report the mapping results for 13 targets. All of these targets show HCO${}^{+}$ emissions, while H${}^{13}$CO${}^{+}$ emissions are observed in ten of them. The HCO${}^{+}$ integrated intensity maps of ten targets show clear clumpy structures, and nine targets show clumpy structures in the H${}^{13}$CO${}^{+}$ maps. Using the RADEX radiative transfer code, we estimate the column density of H${}^{13}$CO${}^{+}$, and determine the abundance ratio [H${}^{13}$CO${}^{+}$]/[H${}_2$] to be approximately 10${}^{-12}$ to 10${}^{-10}$. Based on the asymmetry of the HCO${}^{+}$ line profiles, we identify 11 targets show blue profiles, while six clumps have global infall evidence. We use the RATRAN and two-layer models to fit the HCO${}^{+}$ line profiles of these infall sources, and analyze their spatial distribution of the infall velocity. The average infall velocities estimated by these two models are 0.24 -- 1.85 km s${}^{-1}$ and 0.28 -- 1.45 km s${}^{-1}$, respectively. The mass infall rate ranges from approximately 10${}^{-5}$ to 10${}^{-2}$ M${}_{\odot }$ yr${}^{-1}$, which suggests that intermediate- or high-mass stars may be forming in the target regions.