Chemical Tracers of Pre-Brown Dwarf Cores Formed Through Turbulent Fragmentation

TL;DR

This study uses chemical modeling to identify molecular tracers that distinguish pre-brown dwarf cores formed via turbulent fragmentation from those formed by freefall collapse, aiding understanding of brown dwarf formation mechanisms.

Contribution

It introduces a chemical tracer-based method to differentiate formation mechanisms of brown dwarf cores, focusing on turbulence-induced fragmentation.

Findings

Cores formed by turbulence are bright in CO and NH₃ but not in HCO⁺.

Pure freefall collapse models show detectable transitions in all three molecules.

Chemical signatures can serve as diagnostics for formation processes.

Abstract

A gas-grain time dependent chemical code, UCL\_CHEM, has been used to investigate the possibility of using chemical tracers to differentiate between the possible formation mechanisms of brown dwarfs. In this work, we model the formation of a pre-brown dwarf core through turbulent fragmentation by following the depth-dependent chemistry in a molecular cloud through the step change in density associated with an isothermal shock and the subsequent freefall collapse once a bound core is produced. Trends in the fractional abundance of molecules commonly observed in star forming cores are then explored to find a diagnostic for identifying brown dwarf mass cores formed through turbulence. We find that the cores produced by our models would be bright in CO and NH$_3$ but not in HCO$^+$. This differentiates them from models using purely freefall collapse as such models produce cores that would have detectable transitions from all three molecules.