Nowadays the exploration of the Universe can be performed by a variety of observational probes and methods over a wide range of the wavelengths: the temperature anisotropy map of the cosmic microwave background (CMB), the Hubble diagrams of nearby galaxies and distant Type Ia supernovae, wide-field photometric and spectroscopic surveys of galaxies, the power spectrum and abundances of galaxy clusters in optical and X-ray bands combined with the radio observation through the Sunyaev–Zel’dovich effect, deep surveys of galaxies in sub-mm, infrared, and optical bands, quasar surveys in radio and optical, strong and weak lensing of distant galaxies and quasars, high-energy cosmic rays, and so on. Undoubtedly gamma-rays, neutrinos, and gravitational radiation will join the above already crowded list.
Among those, optical galaxy redshift surveys are the most classical. Indeed one may phrase that the
modern observational cosmology started with a sort of galaxy redshift survey by Edwin Hubble. Still galaxy
redshift surveys are of vital importance in cosmology in the 21st century for various reasons:
With the above in mind, we will attempt to summarize what we have learned so far from galaxy redshift surveys, and then describe what will be done with future data. The review is organized as follows. We first present a brief overview of the Friedmann model and gravitational instability theory in Section 2. Then we describe the non-Gaussian nature of density fluctuations generated by the nonlinear gravitational evolution of the primordial Gaussian field in Section 3. Next we discuss the spatial biasing of galaxies relative to the underlying dark matter distribution in Section 4. Our understanding of biasing is still far from complete, and its description is necessarily empirical and very approximate. Nevertheless this is one of the most important ingredients for proper interpretation of galaxy redshift surveys. Section 5 introduces general relativistic effects which become important especially for galaxies at high redshifts. We present the latest results from the two currently largest galaxy redshift surveys, 2dF (Two Degree Field) and SDSS (Sloan Digital Sky Survey), in Section 6. Finally, Section 7 is devoted to a summary of the present knowledge of our Universe and our personal view of the future direction of cosmological researche in the new millennium.
© Max Planck Society and the author(s)