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date: 28 February 2024

selection function 

The Oxford Companion to Cosmology

Andrew Liddle,

Jon Loveday

Most astronomical surveys select objects by their observed flux (or equivalently, apparent magnitude). Since observed flux decreases as the square of distance, only the most intrinsically luminous objects will appear at large distance in such a survey, and, since such luminous objects are rare, the overall space density of objects decreases with distance. The selection function of a survey gives the probability that an object within a given luminosity range will be included in the survey, as a function of distance or redshift. The selection function generally decreases smoothly from one at low redshift, where all objects in the luminosity range will be included, to zero at large redshift, where there are no objects of sufficiently high luminosity to be included.... ...

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