Modelling of Irradiated Molecular Clouds

We offer free web-access to our pre-calculated PDR parameter grid that can be accessed through the KOSMA-tau Webinterface

We simulate observations of size distributions of clumps mimicking the fractal structure of the ISM.



A particular strength of the KOSMA-τ PDR-model is the simulation of full size distributions of clumps mimicking the fractal structure of the molecular gas in star-forming regions.

Understanding the physics and chemistry of PDRs

By comparing PDR observations with the model predictions we will understand the essential PDR properties:

Energy balance of PDRs

  • the gas heating efficiency
  • the origin of CII 158 µm emission
  • the role of H2O cooling
  • the role of dust heating and cooling

Photo-induced chemistry

  • abundance profiles of light hydrides
  • H3O+ as central node in the chemical network
  • the influence of X-rays
  • sources of endothermic hydride formation
  • the role of surface-reactions and time-dependent chemistry

PDR dynamics and kinematics

  • the turbulent pressure distribution from HII regions to molecular clouds
  • the impact of advection and turbulence
  • the photo-evaporation of PDRs

Work plan

The main work goes into the improved modelling of the microphysical and chemical processes in the KOSMA-tau PDR model. This means in particular:

  • to extend the dust treatment to cover arbitrary dust distributions,
  • to improve the treatment of H2 formation
  • to include surface reactions into the chemical network
  • to include time-dependent chemistry to model the impact of ice evaporation, advection flows, progressing ionization fronts, and turbulent mixing

Current activities

In this application period we:

  • perform updates to the chemistry
  • include a parametrized description of surface reaction rates in a steady-state chemical network,
  • improve the dust treatment including surface reactions,
  • add a wavelength dependent UV transfer
  • model the H2 emission
  • study the pressure and energy balance in the PDRs.

In the longer perspective we will switch to a timedependent PDR model which is able to simulate all dynamic effects that can be deduced from the observed line profiles.  By comparing this advanced model with the observational data we will be able to resolve the chemical structure and energy balance of interstellar gas in a highly inhomogeneous medium, understand the interplay between turbulent motions and radiative processes for the chemical evolution of the gas, and finally quantify the impact of UV radiation in the evolution of molecular clouds towards star formation.