Power correlations in cosmology: limits on primordial non-Gaussian density fields
We probe the statistical nature of the primordial density field by measuring correlations between the power in adjacent Fourier modes. For certain types of non-Gaussian field, these k-space correlations would be expected to be more extended than for a Gaussian field, providing a useful discriminatory test for Gaussian fields. We apply this test to the combined QDOT and 1.2-Jy IRAS galaxy survey and find the observed density field to be in good agreement with having Gaussian density fluctuations for modes with k < 0.1 h/Mpc. From this result we are able to set quantitative limits on a class of possible non-Gaussian distributions -- the product of a Gaussian field with an independent stochastic field. The maximum sensitivity is to modulations of a Gaussian field with coherence scales of 30 Mpc/h and the rms modulation on this scale cannot greatly exceed unity. We discuss the improvements to this limit likely to be set by future surveys.