Modelling of Irradiated Molecular Clouds

  • Our Team

  • PD Dr. Volker Ossenkopf-Okada (PI, PH1)
  • PD Dr. Markus Röllig (PH1)
  • Christoph Bruckmann (PH1)
  • Dr. Yoko Okada (PH1)
  • Dr. Robert Simon (PH1)
  • Prof. Jürgen Stutzki (PH1)

A short overview

Project C1 tries to understand the local chemistry and physics in photon-dominated regions (PDRs), these are molecular clouds affected by the UV radiation from young stars, by means of constructing a sophisticated PDR model that fits the observations of cooling lines and continuum radiation. The model includes all relevant chemical and microphysical processes and a flexible geometry adaptable to any star-forming region. It represents the main tool to interpret the line and continuum radiation from these regions that is typically observed at far-infrared and radio wavelengths. By iteratively improving the existing PDR model code and fitting observed data with the model output this project will help to understand all processes governing the structure and emission of the extended gas in star-forming regions.

By developing a flexible three-dimensional model based on cells of clumpy PDR ensembles we predict the line
emission from individual, UV illuminated cores up to the structure of whole galaxies. This approach will be used on the subgrid level to be combined with the dynamical models in subprojects C5 and C6. This allows us to focus in the new application period on the impact of dynamic effects. After the fitting of individual velocity structures and dust surface effects in the current period we will investigate the impact of varying initial conditions and the effects of turbulent mixing.

The project will also focus on the expected observations of the James Webb Space Telescope, which will resolve
all details of the distribution of PAHs and warm H2 across the PDRs. By comparing the spatial distribution of the PAHs and their charging state with the local heating traced by the cooling lines we will quantify the photoelectric
effect and the H2 formation at the level of individual dust and PAH structures.

The results of project C1 are used to interpret the observations taken in projects A1-A5, where PDR material is observed in Galactic regions and in external galaxies. At the same time these observations serve as calibration for the PDR model. The treatment of dust-surface chemistry is based on results obtained in C3. Project C4 accesses the PDR database in order to calibrate and refine its numerical approach to the computation of the local thermal balance in galaxy formation. The instrumental developments planned in project group D will enable heterodyne observations of the OI 63µm line, the main PDR cooling line at high densities.

Selected Publications


In 2017

Andree-Labsch, S.; Ossenkopf-Okada, V.; Röllig, M., Modelling clumpy photon-dominated regions in 3D. Understanding the Orion Bar stratification. A&A 2017, 598, A2

Glück, C.B.; Stutzki, J.; Röllig, M.; et al., SOFIA/GREAT [C ii] observations in nearby clouds near the lines of sight towards B0355+508 and B0212+735. A&A 2017, 600, A94.

Nagy, Z.; Choi, Y.;  Ossenkopf-Okada, V.; et al., Herschel/HIFI spectral line survey of the Orion Bar. Temperature
and density differentiation near the PDR surface. A&A 2017, 599, A22

Veltchev, T.V.; Ossenkopf-Okada, V.; Stanchev, O.; et al., Spatially associated clump populations in Rosette from CO and dust maps, MNRAS, 2018, 475, 2215

In 2016

Röllig, M.; Simon, R.; Güsten, R.; et al., [C II] 158 μ m and [N II] 205 μ m emission from IC 342. Disentangling the emission from ionized and photo-dissociated regions. A&A 2016, 591, A33

M. Röllig, Violent emissions of newborn stars. Nature 2016, 537, 174

In 2015

Nagy, Z.; Ossenkopf, V.; van der Tak, F.F.S, et al., C2H observations toward the Orion Bar. A&A 2015, 578, A124

Koumpia,  E.; Harvey, P.M.; Ossenkopf, V.;  et al., Temperatures of dust and gas in S 140. A&A, 2015, 580, A68

Ossenkopf, V.; Koumpia, E.; Okada, Y., et al., Fine-structure line deficit in S 140. A&A, 2015, 580, A83

Pérez-Beaupuits, J.P.; , Güsten, R.; Spaans, M., Ossenkopf, V.; et al., Disentangling the excitation conditions of the dense gas in M17 SW. A&A 2015, 583, A107

Pérez-Beaupuits, J.P.; Stutzki, J.;  Ossenkopf, V.; et al., Detection of a large fraction of atomic gas not asso-
ciated with star-forming material in M17 SW. A&A 2015, 575, A9

In 2014

Beuther, H.; Ragan, S. E.; Ossenkopf, V.; et al.; Carbon in different phases ([CII], [CI], and CO) in infrared dark clouds: Cloud formation signatures and carbon gas fractions, A&A, 2014, 571, 53

In 2013
Ossenkopf, V.; Röllig, M.; Neufeld, D.; et al., Herschel/HIFI observations of [CII] and [ 13CII] in PDRs, A&A, 2013, 550, 57.

Röllig, M.; Ossenkopf, V., Carbon Fractionation in PDRs, A&A, 2013, 550, 56

van der Tak, F. F. S.; Nagy, Z.; Ossenkopf, V.; et al., Spatially extended OH+ emission from the Orion Bar and Ridge, A&A, 2013, 560, 95-104

Nagy, Z.; Van der Tak, F. F. S.; Ossenkopf, V.; et al. The chemistry of ions in the Orion Bar I. - CH+, SH+, and CF+. The effect of high electron density and vibrationally excited H2 in a warm PDR surface, A&A, 2013, 550, 96-106

Okada, Y.; Pilleri, P.; Berné, O.; Ossenkopf, V.; et al., Probing the role of polycyclic aromatic hydrocarbons in the photoelectric heating within photodissociation regions, A&A, 2013, 553, 2