Gas kinematics in 70 μm dark molecular clumps with ammonia

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Abstract
We present an investigation of the gas kinematics and an assessment of 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 of N_ ̊m uv ∼ 10^ 44 s -1 for the Lyman continuum photons indicates that the four IRDCs are in very early evolutionary stages, where free-free emission is still absent. We identified 61 dense cores at the size scale of ∼0.1 pc using the inner satellite groups of ) increases with an 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 AGAL 031.024+00.262 and one core in AGAL 024.314+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 undergoing collapse. Conversely, there are seven dense cores in AGAL031.024+00.262 displaying a decrease in 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 (σ_ non non with increasing radial distance from the center. By comparing this trend 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 subparsec scales are essential to reveal the transition from thermal- to nonthermal-dominated regions, especially in dense cores associated with multiple velocity components.
Funding Information
  • National Key Research and Development Program of China (2023YFA1608204)
  • National Natural Science Foundation of China (12550003)
  • Guangxi Talent Programme
  • National SKA Program of China (2025SKA0140100)
  • Double First-Class (14912217)
  • National Natural Science Foundation of China (13004007)

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