Influence of H2 formation on PDR model results

1. Influence of H2 formation on PDR model results M. Röllig V. Ossenkopf, C. Glück Universität zu Köln, Germany CO Ladder Workshop - Leiden 2012

2. Outline • H2formation on grain surfaces • chemisorption vs. physisorption • H2 formation efficiencies on different dust sorts • chemical H2 heating & cooling • effects on clump structure CO Ladder Workshop - Leiden 2012

3. Introduction Numerical PDR models of proved to be a valuable tools in analyzing and understanding the local conditions in massive star forming regions. Hollenbach & Tielens, 1999, R.o.m.P., 71 Ossenkopf et al, 2010, A&A 518, L79v CO Ladder Workshop - Leiden 2012

4. Introduction Yet, here be dragons... • complex physics / chemistry • complex/unknown local conditions Röllig et al. 2007, A&A, 467 θ1Ori C (O6) CO Ladder Workshop - Leiden 2012

5. Introduction and unfortunately, deficient input data • missing experimental data • inter/extrapolation CO Ladder Workshop - Leiden 2012

6. H2 formation on grain surfaces CO Ladder Workshop - Leiden 2012

7. H2 formation on grain surfaces • H atoms hitting grain surfaces can stick weakly (physisorption) or strongly (chemisorption) bound. • Td>100 K desorption overcomes binding and H2 formation efficiency →0 • Chemisorbed H atoms can effectively form H2 up to Td>500K • we implemented the formalism presented by Cazaux & Tielens (2002,2004) in the KOSMA- chemistry. CO Ladder Workshop - Leiden 2012

8. H2 formation efficiency Cazaux & Tielens 2004, ApJ 604 CO Ladder Workshop - Leiden 2012

9. H2 formation efficiency Cazaux & Tielens 2004, ApJ 604 CO Ladder Workshop - Leiden 2012

10. H2 formation efficiency Cazaux & Tielens 2004, ApJ 604 CO Ladder Workshop - Leiden 2012

11. H2 formation efficiency Cazaux & Tielens 2004, ApJ 604 CO Ladder Workshop - Leiden 2012

12. H2 formation rate total formation rate depends on total dust surface CO Ladder Workshop - Leiden 2012

13. H2 formation rate Weingartner andDraine, 2001, ApJ 548 CO Ladder Workshop - Leiden 2012

14. H2 formation rate CO Ladder Workshop - Leiden 2012

15. H2 heating/cooling • H2 binding energy 4.5 eV → H2 formation heating • kinetic H2 dissociation cooling (Lepp & Shull, 1983, ApJ 270, 578) H2 + H → H + H + H - 4.5eV H2 + H2 → H2 + H + H - 4.5eV Alternatively: sticking coeff. CO Ladder Workshop - Leiden 2012

16. H2 heating/cooling Le Bourlot et al. 2012 CO Ladder Workshop - Leiden 2012

17. H2 heating/cooling Le Bourlot et al. 2012 CO Ladder Workshop - Leiden 2012

18. H2 heating/cooling A: R=const, B: only LH, C=LH+ER Le Bourlot et al. 2012 CO Ladder Workshop - Leiden 2012

19. H2 heating/cooling Le Bourlot et al. 2012 A: R=const, B: only LH, C=LH+ER CO Ladder Workshop - Leiden 2012

20. Dust influence CO Ladder Workshop - Leiden 2012

21. Dust influence radiativetransfereffect H2chemistryeffect CO Ladder Workshop - Leiden 2012

22. Dust influence • H2 binding energy 4.5 eV → H2 formation heating • kinetic H2 dissociation cooling (Lepp & Shull, 1983, ApJ 270, 578) H2 + H → H + H + H - 4.5eV H2 + H2 → H2 + H + H - 4.5eV • large effect on H-H2 transition region chemistry CO Ladder Workshop - Leiden 2012

23. Dust influence • H2 binding energy 4.5 eV → H2 formation heating • kinetic H2 dissociation cooling (Lepp & Shull, 1983, ApJ 270, 578) H2 + H → H + H + H H2 + H2 → H2 + H + H • large effect on H-H2 transition region chemistry • chemistry  physics CO Ladder Workshop - Leiden 2012

24. Summary • Great need for reliable (astrochemistry) data • Lab results need to be robust against different modeling applications • Growing understanding of dust properties and H2 formation process dramatically influences model results • chemistry and physics strongly connected to each other CO Ladder Workshop - Leiden 2012