Surveys of clumps, cores, and condensations in Cygnus X

Abstract

Context. 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. Aims. We aim to characterize the temperature, velocity dispersion, and fragmentation of the MDCs in the Cygnus X giant molecular cloud and to investigate the stability and dynamics of these cores. Methods. We present the Karl G. Jansky Very Large Array (VLA) observations of the NH3 (J, K) = (1,1) and (2,2) inversion lines towards 35 MDCs in Cygnus X, from which we calculated the temperature and velocity dispersion. We extracted 202 fragments (~0.02 pc) from the NH3 (1,1) moment-0 maps with the GAUSSCLUMPS algorithm. We analyzed the stability of the MDCs and their NH3 fragments through evaluating the corresponding kinetic, gravitational potential, and magnetic energies and the virial parameters. Results. The MDCs in Cygnus X have a typical mean kinetic temperature TK 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 NH3 fragments, with TK ~19 K, their nonthermal velocity dispersions are mostly trans-sonic to subsonic. Unless there is a strong magnetic field, most NH3 fragments are probably not in virialized states. We also find that most of the NH3 fragments are dynamically quiescent, while only a few are active due to star formation activity.