Correlations in the Lyα forest:: Testing the gravitational instability paradigm

We investigate correlations between the long wavelength fluctuations and the small-scale power in the Ly alpha forest. We show that such correlations can be used to discriminate between fluctuations induced by large-scale structure and those produced by nongravitational processes such as fluctuations in the continuum of the quasar. The correlations observed in Q1422+231 are in agreement with the predictions of numerical simulations, indicating that nongravitational fluctuations on large scales have to be small compared to those induced by the large-scale structure of the universe, contributing less than 10% (95% confidence) of the observed power. We also show the sensitivity of such statistics to the equation of state of the gas and its mean temperature.