Chemical and Physical Conditions in Molecular Cloud Core DC 000.4-19.5 (SL42) in Corona Australis

TL;DR

This study investigates the chemical and physical properties of the starless molecular cloud core DC 000.4-19.5 in Corona Australis, revealing gas depletion, core structure, and chemical model consistency through observations and analysis.

Contribution

It provides detailed observational data and analysis of the core's structure, temperature, and chemical composition, comparing models and observations to understand core evolution.

Findings

Gas phase depletion of CO at high extinctions.

Core structure deviates from Bonnor-Ebert sphere, indicating gravitational binding.

Steady-state depletion model matches observed molecular profiles.

Abstract

Chemical reactions in starless molecular clouds are heavily dependent on interactions between gas phase material and solid phase dust and ices. We have observed the abundance and distribution of molecular gases in the cold, starless core DC 000.4-19.5 (SL42) in Corona Australis using data from the Swedish ESO Submillimeter Telescope. We present column density maps determined from measurements of C18O(J=2-1,1-0) and N2H+(J=1-0) emission features. Herschel data of the same region allow a direct comparison to the dust component of the cloud core and provide evidence for gas phase depletion of CO at the highest extinctions. The dust color emperature in the core calculated from Herschel maps ranges from roughly 10.7 to 14.0 K. This range agrees with the previous determinations from Infrared Space Observatory and Planck observations. The column density profile of the core can be fitted with a Plummer-like density distribution approaching n(r) ~ r^{-2} at large distances. The core structure deviates clearly from a critical Bonnor-Ebert sphere. Instead, the core appears to be gravitationally bound and to lack thermal and turbulent support against the pressure of the surrounding low-density material: it may therefore be in the process of slow contraction. We test two chemical models and find that a steady-state depletion model agrees with the observed C18O column density profile and the observed N(C18O) versus AV relationship.