Correlations in the Lyman alpha forest: testing the gravitational instability paradigm

We investigate correlations between the long wavelength fluctuations and the small scale power in the Lyman alpha forest. We show that such correlations can be used to discriminate between fluctuations induced by large scale structure and those produced by non-gravitational processes such as fluctuations in the continuum of the quasar or in the temperature of the gas. The correlations observed in Q1422+231 are in agreement with the predictions of numerical simulations, indicating that non-gravitational fluctuations on large scales have to be small compared 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.