A Study Of Infall In Massive Clumps And Physical And Chemical Properties In I14498 Clumps

Thirty massive clumps associated with bright infrared sources were observed to detect the infall signatures and characterize infall properties in the envelope of the massive clumps by APEX telescope in CO(4-3)and C¹⁷O(3-2)lines.Eighteen objects have“blue profile”in CO(4-3)line,with the line asymmetric parameters less than–0.25 and virial parameter less than 2,,suggesting that global collapse is taking place in these massive clumps.The CO(4-3)lines were fitted by the two-layer model in order to obtain infall velocities and mass infall rates.Derived mass infall rates are from 10^-3M_?yr^-1to 10^-1M_?yr^-1.A positive relationship between clump mass and infall rate appears to indicate that gravity plays a dominant role in the collapsing process.Higher luminosity clump has larger mass infall rate,implying that the clump with higher mass infall rate has higher star formation rate.There is no correlation between luminosity-mass ratio and mass infall rate,implying that gas infall can occur at various evolutionary stage.To explore the physical and chemical properties of sources in this region,one of the col-lapse sources,I14498,has been studied by the ALMA telescope with higher spatial resolution and its physical and chemical properties have been analyzed.Derived gas mass of I14498 is29.27 M_?and the hydrogen column density is 1.41×10²⁴cm^-2,indicating that I14498 is a massive star formation region.The linear scale of the protostellar core of I14498 is 0.03 pc by continuous spectrum Gaussian fitting.It is rich in chemical property,with more than 150transition lines from 24 molecular species detected.The gas temperature is approximate 100 K.The characteristics of I14498 is high temperature,small scale and rich chemical composition,which indicates that this region is in hot core stage of star formation.According to the gas dis-tribution diagram of multiple transition lines containing nitrogen,oxygen and sulfur fractions,we found that most molecular gas distribution and dust distribution are highly coupled.This suggests that the molecules in I14498 originate from the chemical composition on the surface of the dust particles.The optical thick lines in I14498 show“blue profile”with collapse char-acteristics and wide line wings,suggesting that the collapse and outflow are taking place in this region.