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 H13CO+ (1–0) lines in order to search for evidence of gas infall in clumps. In this paper, we report the mapping results for 13 targets. All of these targets show HCO+ emissions, while H13CO+ emissions are observed in 10 of them. The HCO+ integrated intensity maps of 10 targets show clear clumpy structures, and nine targets show clumpy structures in the H13CO+ maps. Using the RADEX radiative transfer code, we estimate the column density of H13CO+, and we determine the abundance ratio [H13CO+]/[H2] to be approximately 10−12–10−10. Based on the asymmetry of the HCO+ line profiles, we identify 11 targets that show blue profiles, while six clumps have evidence of global infall. 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 ⊙ yr−1, which suggests that intermediate- or high-mass stars may be forming in the target regions.