Astrophysics (index)

Luminosity Function

(function giving number of stars or galaxies at different luminosities)

A Luminosity Function is an empirical density/mass-style function that yields the number of stars or galaxies at each given Luminosity (L).

A common form is the Schechter Luminosity Function for galaxies (aka Schechter Function, an example of a Galaxy Luminosity Function), a "modified" Power Law providing a format for such functions:

n(x)dx = ΦSunxae-xdx
  • x - L/LSun (luminosity in solar luminosities).
  • ΦSun - a factor to normalize the Number Density, chosen to match observation, in units of h3/Mpc3 (parameter).
  • a - a power, chosen to match observation (parameter).
  • h - normalized Hubble Constant (H0).

Some typical values of the plug-in parameters:

  • a = -1.25
  • ΦSun = 1.2 × 10-3

Other variations of luminosity functions are Globular Cluster (GC) Luminosity Functions, Galaxy Cluster (CL) luminosity functions, and luminosity functions of particular bands, or lines, or the lines of a specific molecule (e.g., Carbon Monoxide (CO)).

Luminosity functions also are assumed to evolve, e.g., to vary with Redshift (z).


Referenced by:
Conditional Luminosity Function (CLF)
Initial Mass Function (IMF)