Dust coagulation in star formation with different metallicities

TL;DR

This study investigates dust grain coagulation in star-forming regions across different metallicities, finding that coagulation occurs even at very low metallicities but has limited impact on thermal evolution.

Contribution

It demonstrates that dust coagulation can be neglected in thermal evolution models of pre-stellar cores regardless of metallicity when grain motions are thermal.

Findings

Dust coagulation occurs at metallicities as low as 10^{-6} Z_sun.

H2 formation rate is only affected after most H2 is formed.

Dust opacity changes only when the core becomes optically thick.

Abstract

Dust grains coagulate into larger aggregates in dense gas. This changes their size distribution and possibly affects the thermal evolution of star-forming clouds. We here investigate dust coagulation in collapsing pre-stellar cores with different metallicities by considering the thermal motions of grains. We show that coagulation does occur even at low metallicity $\sim 10^{-6} \Zsun$. However, we also find (i) that the H$_2$ formation rate on dust grains is reduced only after the majority of H$_2$ is formed; and (ii) that the dust opacity is modified only after the core becomes optically thick. Therefore, we conclude that the effects of dust coagulation can safely be neglected in discussing the temperature evolution of the pre-stellar cores for any metallicity as long as the grain motions are thermal.