Galaxy redshift survey

A systematic catalog of galaxy positions and redshifts used to map the three-dimensional distribution of galaxies and large-scale cosmic structure.

Redshift: The increase in a wave’s wavelength as its source moves away or as space expands. Galaxy redshifts provide the distance coordinate that converts angular positions into a three-dimensional map.
Baryon acoustic oscillations: A preferred clustering scale imprinted by sound waves in the early universe and preserved in the distribution of matter. The scale in galaxy clustering acts as a standard ruler for cosmic distances.
Sloan Digital Sky Survey: A major astronomical survey combining imaging and spectroscopy to map galaxies, quasars, and other celestial objects. Its large spectroscopic galaxy sample transformed studies of nearby large-scale structure.
Cosmological redshift: The wavelength stretching of light caused by the expansion of the universe during its journey to Earth. It supplies the dominant distance signal for most galaxies in cosmological surveys.
Photometric redshift: An estimate of an astronomical object’s redshift based on its brightness in multiple broad wavelength bands. Photometric surveys cover many more objects, but their distance estimates are less precise than spectroscopy.
Hubble's law: The relation between a galaxy’s recessional velocity and its distance in the expanding universe. At relatively small cosmological distances, it translates redshift into an approximate distance.
Galaxy clustering: The statistical tendency of galaxies to occur in groups and structures rather than as a uniform distribution. Survey positions quantify clustering across cosmic scales.
2dF Galaxy Redshift Survey: A spectroscopic survey that measured redshifts for about 220,000 galaxies in two wide sky strips. Its map enabled precise measurements of galaxy clustering and the matter power spectrum.
Luminosity distance: The distance defined by the inverse-square relation between an object’s luminosity and its observed flux. It illustrates why cosmological distances inferred from observations depend on the expansion model.
Narrowband imaging: Imaging through a restricted wavelength band that isolates selected emission lines or spectral features. It finds targeted galaxy populations without obtaining a full spectrum for each object.

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