MALT90 molecular content on high-mass IR-dark clumps
  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.
