PSJC #110 March 2, 2012
3D simulations of pillars formation around HII regions: the importance of shock curvature
We will discuss this paper by
P. Tremblin et al. (2012)
The abstract is:
"Aims. Radiative feedback from massive stars is a key process for
understanding how HII regions enhance or inhibit star formation in
pillars and globules at the interface with molecular clouds. We aim
to contribute by modelling the interactions between ionization and gas
clouds to better understand the processes at work. We study in detail
the impact of modulations on the cloud-HII region interface and density
modulations inside the cloud.
Methods. We ran 3D hydrodynamical simulations based on Euler equations
coupled with gravity using the HERACLES code. We implemented a method to
solve ionization/recombination equations and took into account typical
heating and cooling processes at work in the interstellar medium that
are caused by ionization/recombination physics.
Results. UV radiation creates a dense shell compressed between an
ionization front and a shock ahead. Interface modulations produce a
curved shock that collapses on itself, which leads to stable growing
pillar-like structures. The narrower the initial interface modulation,
the longer the resulting pillar. We interpret pillars resulting from
density modulations in terms of the ability of these density modulations
to curve the shock ahead of the ionization front.
Conclusions. The shock curvature is a key process for understanding
the formation of structures at the edge of HII regions. Interface and
density modulations at the edge of the cloud have a direct impact on
the morphology of the dense shell during its formation. Deeper inside
the cloud, structures have less influence because of the high densities
reached by the shell during its expansion."