Age, size, and position of H ii regions in the Galaxy. Expansion of
  ionized gas in turbulent molecular clouds
  This work aims at improving the current understanding of the interaction
between H ii regions and turbulent molecular clouds. We propose a new method to
determine the age of a large sample of OB associations by investigating the
development of their associated H ii regions in the surrounding turbulent
medium. Using analytical solutions, one-dimensional (1D), and three-dimensional
(3D) simulations, we constrained the expansion of the ionized bubble depending
on the turbulent level of the parent molecular cloud. A grid of 1D simulations
was then computed in order to build isochrone curves for H ii regions in a
pressure-size diagram. This grid of models allowed to date large sample of OB
associations and was used on the H ii Region Discovery Survey (HRDS).
Analytical solutions and numerical simulations showed that the expansion of H
ii regions is slowed down by the turbulence up to the point where the pressure
of the ionized gas is in a quasi-equilibrium with the turbulent ram pressure.
Based on this result, we built a grid of 1D models of the expansion of H ii
regions in a profile based on Larson laws. The 3D turbulence is taken into
account by an effective 1D temperature profile. The ages estimated by the
isochrones of this grid agree well with literature values of well-known regions
such as Rosette, RCW 36, RCW 79, and M16. We thus propose that this method can
be used to give ages of young OB associations through the Galaxy such as the
HRDS survey and also in nearby extra-galactic sources.
