The gas kinematics in 70 {\mu}m dark molecular clumps with ammonia
We present the investigation of the gas kinematics and assess the evolutionary stages of dense cores embedded in four infrared dark clouds (IRDCs) using the NH$_3$(1,1) and NH$_3$(2,2) lines obtained from the VLA and GBT observations. There is no 1.3 cm continuum emission counterpart in 1.3 mm continuum emission revealed by the SMA toward these IRDCs. The low production rate $N_{\rm uv} \sim 10^{44}$ s$^{-1}$ of Lyman continuum photons, indicates that the four IRDCs are in very early evolutionary stages, in which free--free emission is still absent. We have identified 61 dense cores at the size scale of $\sim$0.1 pc using the inner satellite groups of NH$_3$(1,1) line. Among them, 38 dense cores exhibit a single velocity component, while 23 dense cores show multiple velocity components. We find that the nonthermal velocity dispersion ($\sigma_{\mathrm{non}}$) increases with increasing radial distance from the center of dense core within the inner 0.1 pc toward eight dense cores, indicating that the turbulence is likely dissipated toward the center of these dense cores. In addition, two dense cores in AGAL031.024+00.262 and one core in AGAL024.314+00.086 exhibit nearly sonic motions on a small scale of 0.01 pc. The weakening of nonthermal support against gravity suggests that these dense cores are close to gravitational collapse or are already collapsing. Conversely, there are seven dense cores in AGAL031.024+00.262 showing a decrease in $\sigma_{\mathrm{non}}$ with increasing radial distance from the center. By comparing this trends with the outflow revealed by CO J=2-1 line, we find that these cores are likely associated with embedded star formation activities. Higher angular resolution observations on sub-parsec scales are essential to reveal the transition from thermal to nonthermal-dominated regions, especially in dense cores associated with multiple velocity components.