MALT90 molecular content on high-mass IR-dark clumps

Abstract: High mass stars form in groups or clusters within massive cores in dense molecular clumps with sizes of 1pc and masses of 200Msun which are important laboratories for high-mass star formation in order to study the initial conditions. We investigate the physical and chemical properties of high-mass clumps in order to better understand the early evolutionary stages and find targets that show star formation signs. We selected the high-mass clumps from ATLASGAL survey that were identified as dark at 8/24$\mu$m wavelengths and used MALT90 data which provides a molecular line set to investigate the physical and chemical conditions in early evolutionary stages. Eleven sources have significant SiO detection (over 3$\sigma$) which usually indicates outflow activities. Thirteen sources are found with blue profiles in both or either HCO$^+$ and/or HNC lines and clump mass infall rates are estimated to be in the range of 0.2E+3 Msunyr$^{-1}$ $-$ 1.8E-2 Msunyr$^{-1}$. The excitation temperature is obtained as <24K for all sources. The column densities for optically thin lines of H$^{13}$CO$^{+}$ and HN$^{13}$C are in the range of 0.4-8.8(E+12) cm$^{-2}$, and 0.9-11.9(E+12) cm$^{-2}$, respectively, while it is in the range of 0.1-7.5(E+14) cm$^{-2}$ for HCO$^{+}$ and HNC lines. The column densities for N${2}$H$^{+}$ were ranging between 4.4-275.7(E+12) cm$^{-2}$ as expected from cold dense regions. Large line widths of N${2}$H$^{+}$ might indicate turbulence and large line widths of HCO$^{+}$, HNC, and SiO indicate outflow activities. Mean optical depths are 20.32, and 23.19 for optically thick HCO$^{+}$ and HCN lines, and 0.39 and 0.45 for their optically thin isotopologues H$^{13}$CO$^{+}$ and HN$^{13}$C, respectively. This study reveals the physical and chemical properties of 30 high-mass IR-dark clumps and the interesting targets among them based on their emission line morphology and kinematics.