lowZ

LowZ, often written as low-z, is a term used in astronomy to refer to objects with small cosmological redshift, z, indicating that they lie in the nearby universe. In practice, low-z means z much less than 1, with commonly used thresholds around z ≤ 0.3 or z ≤ 0.1 depending on context. In this regime, cosmological expansion is a modest contributor to observed redshifts and peculiar velocities can be a substantial factor.

Redshift z measures the fractional change in wavelength of light from an object. For small z, the relation between recession velocity and redshift is approximately v ≈ cz, and distances can be estimated with Hubble's law, though local motions introduce scatter and complicate interpretation.

Low-z samples are widely used to study the properties of nearby galaxies, star formation, active galactic nuclei, and the local large-scale structure, and to calibrate distance indicators such as Cepheid variables, Type Ia supernovae, and the Tully-Fisher relation. These surveys enable detailed mapping of the local cosmos and serve as a foundation for understanding cosmic evolution.

Challenges include selection biases, extinction due to dust, K-corrections, and the influence of peculiar velocities which can mimic or obscure genuine cosmological redshift, especially at the very lowest z. Careful treatment of these effects is required to derive accurate distances and intrinsic properties.

In practice, many galaxy redshift surveys and imaging programs target the low-z universe to build a detailed picture of the nearby cosmos. See also redshift, Hubble's law, standard candles, and local universe studies.