Simulations of the Lyman Alpha Forest

Gregory Novak, University of California, Santa Cruz

We are adding a parallel fixed grid Eulerian hydrodynamics component to an existing particle-mesh N-body code for self-gravitating matter in an expanding universe. The code will be used to simulate intergalactic gas in the distant past (redshift 2-4) with the goal of reproducing the observed properties of the Lyman alpha forest (LAF). The LAF is a dense set of absorption lines seen in the spectra of distant quasars due to clouds of neutral hydrogen along the line of sight. The detailed structure of the LAF gives information about both the spectrum and the amplitude of density fluctuations in the early universe that gave rise to all present-day structure (Croft et al. 1998, Gnedin and Hamilton 2002).

This information can be combined with cosmic microwave background anisotropy (CMBA) measurements to break degeneracies that exist between cosmological parameters when one considers the CMBA data in isolation. Meiksin and White (2001) showed that it is possible to reproduce the observed properties of the LAF to an accuracy of ten percent using a simple prescription for the behavior of the intergalactic gas rather than outright simulation. However, in light of the recent exquisitely accurate CMBA measurements reported by the Wilkinson Microwave Anisotropy Probe team (Spergel et al. 2003), it is highly desirable to refine the LAF measurements beyond the level of ten percent accuracy through detailed simulation.

Croft, Weinberg, Katz and Hernquist, Astrophysical Journal 495:44 (1998).

Gnedin and Hamilton, Monthly Notices of the Royal Astronomical Society, 334:107 (2002).

Meiksin and White, Monthly Notices of the Royal Astronomical Society, 324:141 (2001).

Spergel et al.,

http://arxiv.org/abs/astro-ph/0302218, Submitted to the Astrophysical Journal, (2003).

Abstract Author(s): G. S. Novak, M. White, and S. M. Faber