EPoS Contribution
EPoS Contribution
Dust and PAH evolution in HII regions

Dmitri Wiebe
INASAN, Moscow, RU
The infrared bubbles identified in Spitzer and WISE observations are mostly associated with HII regions around young massive stars. The IR intensity distributions in these sources show distinct morphologies depending on the wavelength. At 8~micron the IR bubbles usually look like relatively narrow rings or ring segments, while an extended emission toward the inner region is seen at 24 micron. At wavelengths longer than 70 micron these objects are also seen as ring-like structures. The goal of our study is to explain the formation of such IR distributions taking the well-studied RCW 120 nebula. We use a 1D chemo-dynamical model to calculate dynamical, chemical, and thermal evolution of an HII region, accounting for the evolution of dust during the expansion of the HII region. Four discrete dust populations are included in the model, namely, large silicate grains (LG), very small graphite grains (VSG), intermediate size grains (ISG), and polycyclic aromatic hydrocarbons (PAH). We consider both grain drift due to radiation pressure and grain destruction by UV radiation. IR intensity distributions are calculated using the radiative transfer model that takes into account stochastic heating of small grains and PAHs. We show that PAHs responsible for 8 micron emission are not subject to radiative drift and thus must be destroyed inside ionized zone by UV radiation. At the same time, 24 micron emission could be associated with both VSG or ISG grains. In the latter case compact 24 micron rings around centers of HII regions are naturally explained due to weak radial drift of ISG grains. The 100 micron emission can be associated with ISG or LG.
Caption: (left) An three-color infrared image of the HII region RCW 120, with green showing 8 micron emission and red showing 24 micron emission. (right) A theoretical image of an HII region having parameters approximately matching those of RCW 120. Stochastic heating of small grains and PAH destruction are taken into account.
Collaborators:
Y. Pavlyuchenkov, INASAN, Russia
M. Kirsanova, INASAN, Russia
Key publication

Suggested Sessions: Massive Star Formation and Feedback