Interpreting Large Scale Structure Observations

The standard model of large scale structure is considered, in which the structure originates as a Gaussian adiabatic density perturbation with a nearly scale invariant spectrum. The basic theoretical tool of cosmological perturbation theory is described, as well as the possible origin of the density perturbation as a vacuum fluctuation during inflation. Then, after normalising the spectrum to fit the cosmic microwave background anisotropy measured by COBE, some versions of the standard model are compared with a variety of data coming from observations of galaxies and galaxy clusters. The recent COBE analysis of G\'{o}rski and collaborators is used, which gives a significantly higher normalization than earlier ones. The comparison with galaxy and cluster data is done using linear theory, supplemented by the Press-Schechter formula when discussing object abundances of rich clusters and of damped Lyman alpha systems. By focussing on the smoothed density contrast as a function of scale, the observational data can be conveniently illustrated on a single figure, facilitating easy comparison with theory. The spectral index is constrained to $0.6<n<1.1$, and in particle physics motivated models that predict significant gravitational waves the lower limit is tightened to $0.8$. [To appear, Proceedings of Journee Cosmologie, Paris, June 1994]