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 ~5 h-1 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 10 h-1 Mpc cube and line-of-sight interval, respectively. We find that the relation between δF/σF and ⟨δm⟩/σm (where σm and σF are the rms dispersions) has a predicted slope of ~0.6 at δF = 0 that 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 galaxy that is observed in the vicinity of Lyα forest lines of sight.