Particle-Mesh Simulations of the Lyman-Alpha Forest.pdf

a r X i v : a s t r o - p h / 0 0 0 8 2 1 4 v 1 1 5 A u g 2 0 0 0 Preprint-00 Particle-Mesh Simulations of the Lyman-Alpha Forest Avery Meiksin1, Martin White2 1Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK 2Astronomy Department, Harvard University 60 Garden Street, Cambridge, MA 02138 , USA 1 February 2008 ABSTRACT Numerical hydrodynamical simulations have proven a successful means of reproducing many of the statistical properties of the Lyman-Alpha forest as measured in high redshift quasar spectra. Pseudo-hydrodynamical methods based only on simulating the dark matter component have been claimed to yield a comparable level of success. We investigate the degree to which two pseudo-methods, with and without allowing for a pseudo-gas pressure, are able to match the predictions of fully hydrodynamical plus dark matter simulations. We also address the requirements for convergence to the statistics of the spectra and the inferred properties of the Lyman-Alpha forest as a function of resolution and box size. Generally we find it is possible to reach agreement with full hydrodynamic simulations at the 10% level in the cumulative distributions of the flux and absorption line parameter statistics for readily achievable particle and grid numbers, but difficult to do much better. Key words: methods: numerical – intergalactic medium – quasars: absorption lines 1 INTRODUCTION Numerical simulations of structure formation in the universe incorporating hydrodynamics in Cold Dark Matter (CDM) dominated cosmologies have proven very successful in repro- ducing the statistical properties of the Lyα forest as mea- sured in high redshift Quasi-Stellar Object (QSO) spectra (Cen et al. 1994; Zhang, Anninos Norman 1995; Hern- quist et al. 1996; Zhang et al. 1997; Bond Wadsley 1997; Theuns, Leonard Efstathiou 1998a). The high level of statistical agreement suggests that the models are cap- turing the essential physical nature of the absorbi