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 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 H ^13 CO ^+ 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 H ^13 CO ^+ maps. Using the RADEX radiative transfer code, we estimate the column density of H ^13 CO ^+ , and we determine the abundance ratio [H ^13 CO ^+ ]/[H _2 ] 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.

Keywords

• Star formation
• Interstellar medium
• Molecular clouds
• Collapsing clouds