Surveys of clumps, cores, and condensations in Cygnus X. Temperature and nonthermal velocity dispersion revealed by VLA NH3 observations

Abstract

The physical properties, evolution, and fragmentation of massive dense cores (MDCs 0.1 pc) are fundamental pieces in our understanding of high-mass star formation. We aim to characterize the temperature, velocity dispersion, and fragmentation of the MDCs in the giant molecular cloud and to investigate the stability and dynamics of these cores. We present the Karl G. Jansky Very Large Array (VLA) observations of the ($J,K$) = and inversion lines towards 35 MDCs in from which we calculated the temperature and velocity dispersion. We extracted 202 fragments ( 0.02 pc) from the moment-0 maps with the GAUSSCLUMPS algorithm. We analyzed the stability of the MDCs and their fragments through evaluating the corresponding kinetic, gravitational potential, and magnetic energies and the virial parameters. The MDCs in Cygnus X have a typical mean kinetic temperature of 20 K. Our virial analysis shows that many MDCs are in subvirialized states, indicating that the kinetic energy is insufficient to support these MDCs against their gravity. The calculated nonthermal velocity dispersions of most MDCs are at transonic to mildly supersonic levels, and the bulk motions make only a minor contribution to the velocity dispersion. Regarding the fragments, with 19 K, their nonthermal velocity dispersions are mostly trans-sonic to subsonic. Unless there is a strong magnetic field, most fragments are probably not in virialized states. We also find that most of the fragments are dynamically quiescent, while only a few are active due to star formation activity.