 Press–Schechter formalism

The Press-Schechter formalism estimates the halo abundance from the Gaussian probability that a smoothed linear overdensity crosses the spherical-collapse threshold, with a factor of two enforcing total mass conservation.

The Press–Schechter formalism is a theoretical framework used in cosmology to describe the formation of structure in the universe, particularly the statistical properties of dark matter halos and galaxy formation. Developed by SLAC physicists William H. Press and Paul Schechter in 1974, this formalism provides a way to estimate the number density and mass distribution of bound systems, like galaxies and clusters of galaxies, from the primordial density fluctuations in the universe.