Chemical chronology of the Southern Coalsack

TL;DR

This study uses water ice measurements to estimate the ages of dense globules in the Southern Coalsack, aligning with dynamical data, and models their chemical evolution to predict molecular abundances for future testing.

Contribution

It provides a chemical chronometer for globules based on ice column densities and models their chemical evolution to predict molecular abundances.

Findings

Ages of globules are approximately 10^5 years.

Chemical abundances depend on gas density and initial conditions.

Predicted molecular column densities can be tested with observations.

Abstract

We demonstrate how the observed H2O ice column densities toward three dense globules in the Southern Coalsack could be used to constrain the ages of these sources. We derive ages of ~10^5 yr, in agreement with dynamical studies of these objects. We have modelled the chemical evolution of the globules, and show how the molecular abundances are controlled by both the gas density and the initial chemical conditions as the globules formed. Based on our derived ages, we predict the column densities of several species of interest. These predictions should be straightforward to test by performing molecular line observations