The effect of metallicity on the abundances of molecules in protoplanetary disks

TL;DR

This study investigates how varying metallicity levels in protoplanetary disks affect their physical, thermal, and chemical properties, especially focusing on the formation, destruction, and distribution of key molecules.

Contribution

The paper introduces a detailed analysis of metallicity's impact on disk chemistry using the ProoDIMO code, highlighting changes in radiation penetration, temperature, and snowline positions.

Findings

Lower metallicity increases radiation penetration and disk heating.

Chemical abundances generally increase with decreasing metallicity.

Snowlines move outward as metallicity decreases.

Abstract

We study the influence of different metallicities on the physical, thermal, and chemical properties of protoplanetary disks, and in particular on the formation and destruction of carbon-based molecules. With the thermo-chemical code ProoDIMO we investigate the impact of lower metallicities on the radiation field, disk temperature, and the abundance of different molecules (H$_2$O, CH$_4$, CO, CO$_2$, HCN, CN, HCO$^+$ and N$_2$H$^+$). We use a fiducial disk model as a reference model and produce two models with lower metallicity. The resulting influence on different chemical species is studied by analyzing their abundance distribution throughout the disk and their vertical column density. Furthermore, the formation and destruction reactions of the chemical species are studied. The results show a relation between the metallicity of the disk and the strength of the stellar radiation field inside the disk. As the metallicity decreases the radiation field is able to penetrate deeper regions of the disk. As a result, there is a stronger radiation field overall in the disk with lower metallicity which also heats up the disk. This triggers a series of changes in the chemical formation and destruction efficiencies for different chemical species. In most cases, the available species abundances change and have greater values compared to scaled-down abundances by constant factors. Metallicity has a clear impact on the snowline of the molecules studied here as well. As metallicity decreases the snowlines are pushed further out and existing snow rings shrink in size.