Gaseous CO Abundance---An Evolutionary Tracer for Molecular Clouds

TL;DR

This study investigates the CO abundance, depletion, and conversion factor in cold molecular cloud cores, revealing their potential as indicators of cloud evolution through combined dust and molecular line data analysis.

Contribution

It provides the first comprehensive analysis of CO properties in a large sample of cold cores, linking CO abundance to cloud evolutionary stages.

Findings

Median CO abundance is 0.89×10^{-4}

CO depletion factor averages 1.7

CO-to-H2 conversion factor median is 2.8×10^{20} cm^{-2}K^{-1}km^{-1}s

Abstract

Planck cold clumps are among the most promising objects to investigate the initial conditions of the evolution of molecular clouds. In this work, by combing the dust emission data from the survey of Planck satellite with the molecular data of $^{12}$CO/$^{13}$CO (1-0) lines from observations with the Purple Mountain Observatory (PMO) 13.7 m telescope, we investigate the CO abundance, CO depletion and CO-to-H$_{2}$ conversion factor of 674 clumps in the early cold cores (ECC) sample. The median and mean values of the CO abundance are 0.89$\times10^{-4}$ and 1.28$\times10^{-4}$, respectively. The mean and median of CO depletion factor are 1.7 and 0.9, respectively. The median value of $X_{CO-to-H_{2}}$ for the whole sample is $2.8\times10^{20}$ cm$^{-2}$K$^{-1}$km$^{-1}$ s. The CO abundance, CO depletion factor and CO-to-H$_{2}$ conversion factor are strongly (anti-)correlated to other physical parameters (e.g. dust temperature, dust emissivity spectral index, column density, volume density and luminosity-to-mass ratio). To conclude, the gaseous CO abundance can be used as an evolutionary tracer for molecular clouds.