Numerical simulations of Quasar Absorbers

1. Tom Theuns Institute for Computational Cosmology, Durham, UK Department of Physics, Antwerp, Belgium Numerical simulations of Quasar Absorbers IAU 199, Shangai 2005

2. Contents: 1. Lyman-a forest in a CDM universe 2. Numerical simulations a. basics b. initial conditions c. photo-ionisation and all that d. simulation codes 3. Results: successes, problems 4. Future Tom Theuns: Absorber simulations

3. Bi and Davidsen 1997; Bi, Boerner & Chu 1992 Mildly non-linear fluctuations modelled using log-normal model produce absorption lines that look like the observations. Tom Theuns: Absorber simulations

4. Cen & Ostriker 1992: Eulerian hydro + particle PM simulation: filamentary pattern in dark matter + photo-ionised gas produces absorption lines Hubble Volume simulation Tom Theuns: Absorber simulations

5. 2. Numerical simulations: a) Basics 1) Assume Gaussian fluctuations 2) Set-up initial conditions using Zel’dovich approximation 3) Use simulation code to evolve particles/gas distribution into non-linear regime Tom Theuns: Absorber simulations

6. 2. Numerical simulations: b) Initial Conditions Generate such Gaussian field on a grid, and use Zel’dovich approximation to generate particle distribution which represents this density field. Tom Theuns: Absorber simulations

7. 2. Numerical simulations: b) Initial Conditions Using this procedure in a small simulation box may dramatically affect the amount of power represented (Sirko 2005) Tom Theuns: Absorber simulations

8. 2. Numerical simulations: b) Initial Conditions Grafic II Ed Bertschinger implemented the idea by Penn to try to resolve part of the problem by generating the Gaussian field in real space, and imposing the correlation function with convolution Tom Theuns: Absorber simulations

9. 2. Numerical simulations: b) Initial Conditions Craig Booth: implemented Grafic II In nice idl widget. Tom Theuns: Absorber simulations

10. 2. Numerical simulations: b) Initial Conditions Tom Theuns: Absorber simulations

11. 2. Numerical simulations: c) photo-ionisation Tom Theuns: Absorber simulations

12. 2. Numerical simulations: c) photo-ionisation Reionisation heats the Universe to T=104K Tom Theuns: Absorber simulations

13. 2. Numerical simulations: c) photo-ionisation Photo-ionisation heating produces a well-defined r-T relation in the low-density IGM that produces the Lya-forest. (Hui & Gnedin 1997) Tom Theuns: Absorber simulations

14. 2. Numerical simulations: c) photo-ionisation unshocked, photo-ionised gas shocked gas Tom Theuns: Absorber simulations

15. 2. Numerical simulations: d) simulation codes SPH versus Grid based hydro Moving mesh, Hydro-PM Painting gas on top of dark matter distribution Tom Theuns: Absorber simulations

16. 2. Numerical simulations: d) simulation codes SPH: Gadget* (Springel, Yoshida & White) Tree+PM, MPI, Multi-timestep Hydra* (Couchman, Pierrce, Thomas) AP3M, (OpenMP, single timestep) GCD+ (Kawata & Gibson) Tree, “MPI”, Multiple-timestep Steinmetz Grape-SPH, Multiple-timestep Carraro & Lia Tree, MPI, Multiple-timestep Gasoline: Wadsley, Quinn Tree, MPI, Multiple-timestep TreeSPH: Katz & Hernquist A Lava lamp … *: publically available Tom Theuns: Absorber simulations

17. 2. Numerical simulations: d) simulation codes Mesh codes: Flash* (ASC) AMR+MPI, single Enzo* (Bryan & Norman) AMR+MPI, multiple timestep Single grid: Cen & Ostriker, Kravtsov et al (ART) *: publically available Tom Theuns: Absorber simulations

18. 2. Numerical simulations: d) simulation codes Tom Theuns: Absorber simulations

19. 2. Numerical simulations: d) simulation codes Tom Theuns: Absorber simulations

20. 3. Results: successes Mock versus Keck spectrum: which is which? Which statistics to use? Line fitting ,Wavelets Pixel statistics Power-spectrum Tom Theuns: Absorber simulations

21. 3. Results: successes One possible statistic: ‘Voigt profile fitting’ Tom Theuns: Absorber simulations

22. 3. Results: successes Simulated and observed P(NH) look very similar. (Theuns et al ’98, Muecket et al, Dave et al, Cen et al) Tom Theuns: Absorber simulations

23. 3. Results: successes Redshift evolution as function of column density (Theuns et al ’98, Dave et al ’99) Tom Theuns: Absorber simulations

24. 3. Results: successes Line-width (b) and temperature are related Column-density (NH) and density are related Hence can determine r-T relation Schaye et al, Ricotti et al, McDonald et al Tom Theuns: Absorber simulations

25. 3. Results: successes T(z) as expected, but only if reionisation happenend late? Other heating mechanisms? Tom Theuns: Absorber simulations

26. 3. Results: successes Effect of T increase on optical depth evolution Tom Theuns: Absorber simulations

27. 3. Results: successes A wavelet analysis finds no evidence for T fluctuations, but does confirms evidence for T change at z=3.4: He+ reionisation? Theuns et al 2001 Tom Theuns: Absorber simulations

28. 3. Results: successes Fraction of pixels with given flux. McDonald et al ‘99 Tom Theuns: Absorber simulations

29. 3. Results: successes Cowie & Songaila Schaye & Aguirre Pixel Optical Depth method Tom Theuns: Absorber simulations

30. 3. Results: successes Tom Theuns: Absorber simulations

31. 3. Results: successes Flux power spectrum Croft et al, McDonald et al, Viel et al Tom Theuns: Absorber simulations

32. 3. Results: successes Simulations look very realistic: use them to estimate contamination in interpreting metal optical depths, and to compute other sources of bias. Schaye et al, Aguirre et al. Tom Theuns: Absorber simulations

33. 3. Results: successes The inferred Carbon abundance is very sensitive to the assumed shape of the ionising background. There is no clear evidence for evolution with redshift. Schaye et al 2003 Tom Theuns: Absorber simulations

34. 3. Results: successes Simulation with metal enrichment due to galactic winds appears to reproduce the observed CIV-HI scatter Theuns et al 2001 Tom Theuns: Absorber simulations

35. M82 Mori, Ferrara & Madau Springel & Hernquist Tom Theuns: Absorber simulations

36. 3. Results: problems High precision cosmology:the HII recombination rate. Tom Theuns: Absorber simulations

37. 3. Results: problems Estimate of G from simulations (diamonds) and inferrred from sources (triangles, squares) Bolton et al ’04 Jena et al ‘04 Tom Theuns: Absorber simulations

38. 3. Results: problems Bernardi et al ‘02 Evolution of the optical depth: high vs low resolution. Tom Theuns: Absorber simulations

39. 3. Results: problems Power-spectrum may be strongly affected by few strong lines Viel et al 2004 Tom Theuns: Absorber simulations

40. 3. Results: problems Are the metals in the simulations too hot? Aguirre et al ‘05 Tom Theuns: Absorber simulations

41. 3. Results: problems How much feedback will destroy the Ly a forest? Theuns et al ‘02 Tom Theuns: Absorber simulations

42. 4. The future Better control of numerical limitations (box size, resolution) Metal pollution: where, when, how UV-background in space and time. Properly include rapid evolution of optical depth. Observations: high vs low resolution? Which statistics to use? Tom Theuns: Absorber simulations