1. Ilian T. Iliev Canadian Institute for Theoretical Astrophysics/University of Zurich with Garrelt Mellema (Stockholm), Jane Arthur, Will Henney (UNAM, Morelia), Paul Shapiro (Austin), Andrea Ferrara (SISSA) and Hiroyuki Hirashita (Tsukuba) Dynamical Radiative Feedback in Turbulent Molecular Clouds and DLAs

2. Dynamical HII Region Evolution in Turbulent Molecular Clouds (Mellema, Arthur, Henney, Iliev, Shapiro, ApJ, 647, 397) Tryfid nebula Eagle nebula Problem: massive star forms in a turbulent medium – what is the subsequent dynamical evolution and can it match observed structures?

3. Method and problem setup ➢ Radiative transfer: C2-Ray ray-tracing method (Mellema, Iliev et al. 2006). ➢ Explicitly photon-conserving in time and space. ➢ Non-equilibrium chemistry, heating and cooling. ➢ Fast, precise and efficient. Fully-parallel. ➢ Used for simulating large-scale Cosmic Reionization and radiative feedback on smaller scales. ➢ Hydrodynamics: Riemann solver (Eulderink & Mellema 1995). ➢ ICs: density and velocity fields from 3D simulations of driven turbulence (E. Vasquez-Semadeni et al. 2005). ➢ Star assumed to form at densest point.

4. Dynamical HII Region Evolution in Turbulent Molecular Clouds: Results (Mellema, Arthur, Henney, Iliev, Shapiro, ApJ, 647, 397) Tryfid nebula Eagle nebula simulated images SII (red), H  (green), SIII (blue) RGB movie EL movie

5. Molecular hydrogen in DLA disks (Hirashita et al. 2003, MNRAS) log(n H ) log(T) H 2 distribution in DLA disks is highly inhomogeneous – multiple cold and dense clumps form. Q: What is the effect of UV ionizing radiation on such clumps?

6. Radiative feedback in DLAs (Iliev, Hirashita & Ferrara 2006, MNRAS, 368, 1885) ➢ 2D axisymmetric AMR radiative transfer and gasdynamic simulations. ➢ Non-equilibrium chemistry + cooling of H, He, C, N, O, S,Ne (here all at 0.1 Z solar ). ➢ Propagating I-front encounters a dense gas clump. ➢ H 2 molecule formation on dust grains, including self- shielding effects.

7. Radiative feedback in DLAs (Iliev, Hirashita & Ferrara 2006, MNRAS, 368, 1885) ➢ For soft (stellar) spectrum (e.g. local stellar sources) the I-front triggers collapse through metal cooling instability. I-front is D-type, preceded by a shock. ➢ For high initial column densities the clump becomes extremely dense and cold, self-shields and forms molecules (N H2 ~10 19 ) - all conditions for star formation are satisfied triggered SF.

8. Radiative feedback in DLAs (Iliev, Hirashita & Ferrara 2006, MNRAS, 368, 1885) ➢ For lower initial column densities the clump still becomes very dense and cold, but relatively less dense and only partially self-shielded: conditions for star formation are not met. ➢ Clearer rocket effect is seen, due to smaller mass and stronger photoevaporative outflow back towards source.

9. Radiative feedback in DLAs (Iliev, Hirashita & Ferrara 2006, MNRAS, 368, 1885) ➢ For hard external source spectrum (power-law, e.g. intergalactic background) no collapse is triggered. ➢ Hard photons pre-heat and disperse the clump before the arrival of the I- front. The interplay between the two effects possibly provides a mechanism for regulated star formation?