The effect of radiation pressure on spatial distribution of dust inside HII regions

Shohei Ishiki*, Takashi Okamoto, Akio K. Inoue

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


We investigate the impact of radiation pressure on spatial dust distribution inside HII regions using one-dimensional radiation hydrodynamic simulations, which include absorption and reemission of photons by dust. In order to investigate grain-size effects as well, we introduce two additional fluid components describing large and small dust grains in the simulations. Relative velocity between dust and gas strongly depends on the drag force. We include collisional drag force and coulomb drag force. We find that, in a compact HII region, a dust cavity region is formed by radiation pressure. Resulting dust cavity sizes (~0.2 pc) agree with observational estimates reasonably well. Since dust inside an HII region is strongly charged, relative velocity between dust and gas is mainly determined by the coulomb drag force. Strength of the coulomb drag force is about 2 order of magnitude larger than that of the collisional drag force. In addition, in a cloud of mass 105 M, we find that the radiation pressure changes the grain-size distribution insideHII regions. Since large (0.1 μm) dust grains are accelerated more efficiently than small (0.01 μm) grains, the large-to-small grain mass ratio becomes smaller by an order of magnitude compared with the initial one. Resulting dust-size distributions depend on the luminosity of the radiation source. The large and small grain segregation becomes weaker when we assume stronger radiation source, since dust grain charges become larger under stronger radiation and hence coulomb drag force becomes stronger.

Original languageEnglish
Pages (from-to)1935-1943
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 2018 Feb 21
Externally publishedYes


  • ISM: clouds -HII regions
  • Methods: numerical
  • Radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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