An Etymological Dictionary of Astronomy and Astrophysics
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The high redshift of a quasar which is seemingly physically associated with a galaxy of low redshift.

→ anomalous; → redshift.

The → redshift of a remote object (galaxy, quasar, supenova) due to the expansion of the Universe.

→ cosmological; → redshift.

The change in the wavelength or frequency of electromagnetic radiation in a gravitational field predicted by general relativity.

→ gravitational; → redshift.

A galaxy or quasar having a → redshift larger than about 0.8, corresponding to a → look-back time half the present age of the Universe. The qualifier "high" is, however, relative and depends on context and authors' assessment.

→ high; → redshift; → object.

A redshift characterizing a near-by receding object.

→ low; → redshift.

A shift in the lines of an object's spectrum toward longer wavelengths. Redshift indicates that an object is moving away from the observer. The larger the redshift, the faster the object is moving. Redshift is expressed by z = Δλ/λ = v/c, where λ is the wavelength, Δλ the wavelength shift, v the velocity of the source relative to the observer, and c the → speed of light. When v approaches c, redshift is expressed by the → relativistic formula z = ((1 +v/c)/(1 - v/c))^½ - 1.

→ red; → shift.

The space corresponding to → redshift measurements, as contrasted with real space. See also → redshift space distortion

→ redshift; → space.

The distortion observed in → redshift space of → galaxy clusters caused by peculiar velocities of the members (→ peculiar velocity). In a perfectly homogeneous → Friedmann-Lemaitre Universe the redshifts would accurately measure radial distances from the observer, and the mapping from real space to redshift space would simply be an identity. In an inhomogeneous Universe the peculiar velocities associated with any inhomogeneous structure will introduce a distortion in this mapping (N. Kaiser, 1987, MNRAS 227, 1). See also: → fingers of God, → Kaiser effect.

→ redshift; → space; → distortion;.

A survey of a large region of the sky to measure the redshifts of all the galaxies down to a certain limiting magnitude.

→ redshift; → survey.

The correlation, first established by E. Hubble, between the cosmological recession velocities of galaxies and their distances.

→ redshift; → distance; → relation.

A spectral line whose wavelength does not coincide with its theoretical value and is shifted toward longer wavelengths.

→ red; → shift; → line.

A redshift caused by the → relativistic Doppler effect. → gravitational redshift.

→ relativistic; → redshift.