This paper presents maps of the J=2-1 transition of CO toward the Draco Nebula Intermediate Velocity Cloud (IVC). The maps cover 8500 square arcmin with a velocity resolution of 0.33 km~s−1 and angular resolution of 38", or 0.11 pc at the cloud distance of 600 pc. The mapped area includes all the emission detected by the {\it Herschel} satellite with 250 μm intensity >5 MJy/sr. Previously published observations of the far-IR emission and the 21 cm line of HI are used to derive the column density distribution of H2 and the abundance ratio CO/H2, as well as the distribution of the molecular fraction of hydrogen, which approaches 90\% over much of the brighter parts of the nebula. The CO emission is highly clumpy and closely resembles the structures seen in far-IR images. The kinematics of the CO show supersonic motions between clumps but near-thermal to trans-sonic motions within clumps, consistent with model predictions that the scale length for dissipation of supersonic turbulence should be ∼0.1 pc, mediated by kinematic viscosity and/or ambipolar diffusion. Different parts of the nebula show evidence for a spread of molecular formation timescales of a few 105 years, comparable to the dynamical timescale of the infalling gas. The IVC will likely merge with the Galactic interstellar medium in ∼107 years, and the densest clumps may form an unbound cluster of low-mass stars.
@article{arxiv.2406.01542,
title = {CO in the Draco Nebula: The Atomic-Molecular Transition},
author = {John H. Bieging and Shuo Kong},
journal= {arXiv preprint arXiv:2406.01542},
year = {2024}
}