Redshift survey

These observations are used to measure detailed statistical properties of the large-scale structure of the universe.

In conjunction with observations of early structure in the cosmic microwave background, these results can place strong constraints on cosmological parameters such as the average matter density[1][2] and the Hubble constant.

[3] Generally the construction of a redshift survey involves two phases: first the selected area of the sky is imaged with a wide-field telescope, then galaxies brighter than a defined limit are selected from the resulting images as non-pointlike objects; optionally, colour selection may also be used to assist discrimination between stars and galaxies.

The Great Wall, a vast conglomeration of galaxies over 500 million light-years wide, provides a dramatic example of a large-scale structure that redshift surveys can detect.

These early redshift surveys were limited in size by taking a spectrum for one galaxy at a time; from the 1990s, the development of fibre-optic spectrographs and multi-slit spectrographs enabled spectra for several hundred galaxies to be observed simultaneously, and much larger redshift surveys became feasible.