Infrared Emission and the Destruction of Dust in HII regions

TL;DR

This paper models infrared emission in HII regions, focusing on dust destruction, and compares results with observations to explain IR intensity distributions around young stars.

Contribution

It introduces a self-consistent model including dust destruction and stochastic heating, explaining IR observations of HII regions more accurately.

Findings

Homogeneous PAH models fail to reproduce IR ring structures.

PAH destruction in ionized regions explains observed IR distributions.

Model aligns with observations using realistic PAH destruction times.

Abstract

The generation of infrared (IR) radiation and the observed IR intensity distribution at wavelengths of 8, 24, and 100 micron in the ionized hydrogen region around a young, massive star is investigated. The evolution of the HII region is treated using a self-consistent chemical-dynamical model in which three dust populations are included -- large silicate grains, small graphite grains, and polycyclic, aromatic hydrocarbons (PAHs). A radiative transfer model taking into account stochastic heating of small grains and macromolecules is used to model the IR spectral energy distribution. The computational results are compared with Spitzer and Herschel observations of the RCW 120 nebula. The contributions of collisions with gas particles and the radiation field of the star to stochastic heating of small grains are investigated. It is shown that a model with a homogeneous PAH content cannot reproduce the ring-like IR-intensity distribution at 8 micron. A model in which PAHs are destroyed in the ionized region provides a means to explain this intensity distribution. This model is in agreement with observations for realistic characteristic destruction times for the PAHs.