# The effects of dust evolution on disks in the mid-IR

## TL;DR

This study models how dust evolution in protoplanetary disks affects mid-infrared gas emission lines, revealing significant increases in line fluxes for most species as dust grains grow and settle over millions of years.

## Contribution

It couples dust evolution modeling with thermochemical disk simulations to analyze the impact on observable mid-infrared spectral lines, a novel integrated approach.

## Key findings

- Line fluxes of most species increase with dust evolution.
- C2H2 line fluxes remain low despite detection, indicating complex chemistry.
- CO2 flux increases faster than other species during disk evolution.

## Abstract

In this paper, we couple together the dust evolution code two-pop-py with the thermochemical disk modelling code ProDiMo. We create a series of thermochemical disk models that simulate the evolution of dust over time from 0.018 Myr to 10 Myr, including the radial drift, growth, and settling of dust grains. We examine the effects of this dust evolution on the mid-infrared gas emission, focussing on the mid-infrared spectral lines of C2H2, CO2, HCN, NH3, OH, and H2O that are readily observable with Spitzer and the upcoming E-ELT and JWST. The addition of dust evolution acts to increase line fluxes by reducing the population of small dust grains. We find that the spectral lines of all species except C2H2 respond strongly to dust evolution, with line fluxes increasing by more than an order of magnitude across the model series as the density of small dust grains decreases over time. The C2H2 line fluxes are extremely low due to a lack of abundance in the infrared line-emitting regions, despite C2H2 being commonly detected with Spitzer, suggesting that warm chemistry in the inner disk may need further investigation. Finally, we find that the CO2 flux densities increase more rapidly than the other species as the dust disk evolves. This suggests that the flux ratios of CO2 to other species may be lower in disks with less-evolved dust populations.