Large-scale Correlation of Mass and Galaxies with the Lyα Forest Transmitted Flux

We present predictions of the correlation between the Lyα forest absorption in quasar spectra and the mass within ∼ 5h Mpc (comoving) of the line of sight, using fully hydrodynamic and hydro-PM numerical simulations of the cold dark matter model supported by present observations. The observed correlation based on galaxies and the Lyα forest can be directly compared to our theoretical results, assuming that galaxies are linearly biased on large scales. Specifically, we predict the average value of the mass fluctuation, < δm >, conditioned to a fixed value of the Lyα forest transmitted flux δF , after they have been smoothed over a 10h −1 Mpc cube and line of sight interval, respectively. We find that < δm > /σm as a function of δF /σF has a slope of 0.6 at this smoothing scale, where σm and σF are the rms dispersions (this slope should decrease with the smoothing scale). We show that this value is largely insensitive to the cosmological model and other Lyα forest parameters. Comparison of our predictions to observations should provide a fundamental test of our ideas on the nature of the Lyα forest and the distribution of galaxies, and can yield a measurement of the bias factor of any type of galaxies that are observed in the vicinity of Lyα forest lines of sight. Subject headings: cosmology: theory—intergalactic medium—large-scale structure of universe—quasars: absorption lines Department of Physics, Princeton University, Princeton, NJ 08544; [email protected] Department of Astronomy, The Ohio State University, Columbus, OH 43210; [email protected] Princeton University Observatory, Princeton University, Princeton, NJ 08544; [email protected]