Physical processes in the ISM

3D Modelling of Clumpy PDRs: the Structure of the ISM in Star Forming Regions

Not scheduled

5h

MPE

Poster

Speaker

Silke Andree (1. Physikalisches Institut, Universität zu Köln)

Description

Photon-dominated regions (PDRs), in which the interstellar far-UV radiation field determines the energy balance and the chemistry of the ISM, form the interface between HII regions and molecular clouds. PDR emission dominates the infrared and sub-millimetre spectra in star forming regions. To understand the interplay between far-UV radiation and star formation in molecular clouds it is necessary to constrain the physical conditions and the intrinsic structure of molecular clouds and PDRs. The KOSMA-tau PDR model has been developed to simulate the line emission from spherical "clumps" in the ISM. Furthermore, it has been shown that a superposition of such clumps, a "clumpy ensemble", embedded in a thin and homogeneous inter-clump medium, can be used to mimic the structure of the ISM. We show that by assembling a 3-dimensional compound from different clumpy ensembles, we can construct a 3-dimensional model to simulate the velocity dependent emission of clumpy PDRs in arbitrary geometric setups. The model supports the analysis of the spatial structure of star forming regions and can simulate the effect of variations in the total mass, the density of the individual components and the ambient far-UV field strength for the different clumpy ensembles within one star forming region. Furthermore, the effect of the opacity of the clumpy structures is discussed theoretically and the resulting line absorption is included into the simulations. This step refines the fit of observational maps and improves the simulation of line profiles. Far-UV absorption in the clouds is dominated by absorptions due to dust grains. Inclusion of these, based on realistic grain-size distributions, will be investigated aiming for the reproduction of the observed ?chemical stratification?, i.e. the occurrence of different line emission at different optical depth. For testing purposes the new model is used to simulate the main cooling lines and other diagnostics of a well known PDR, namely the Orion Bar. Through the fit of observational maps and line profiles we are able to constrain the spatial variation of the PDR parameters. In addition we can test our understanding of the clumpy structure of the ISM and perform a major step towards a fully self-consistent model of typically highly inhomogeneous PDRs.