Initial mass function

The initial mass function describes the number of stars formed in each mass range within a stellar population. It is typically represented as a distribution that declines toward higher stellar masses.

Salpeter initial mass function: A power-law initial mass function with logarithmic slope −1.35 for stars more massive than about one solar mass. Its high-mass power law is the classic approximation used to model this distribution.
Star formation rate: The mass of gas converted into stars per unit time in a region or galaxy. Inferring this rate from light requires assumptions about how many stars form at each mass.
Edwin Salpeter: An Austrian-American astrophysicist who derived a power-law distribution for stellar masses in 1955. His result established the classic high-mass form used to describe newly formed stars.
Universality of the initial mass function: The hypothesis that the initial mass function has the same form across different star-forming environments. Environmental variations would change the basic assumption behind many population calculations.
Kroupa initial mass function: A piecewise power-law initial mass function with a shallower slope at low stellar masses. Its changing slopes capture the distribution across both low- and high-mass stars.
Galaxy luminosity function: A distribution describing the number of galaxies as a function of their luminosity. The initial mass function affects the stellar light used to derive galaxy luminosities.
Peter Kroupa: An astronomer known for developing a piecewise power-law model of stellar masses at birth. His formulation refined the distribution, especially among low-mass stars.
Integrated galactic initial mass function theory: A theory in which a galaxy-wide mass distribution emerges from environment-dependent stellar populations. It offers one explanation for why galaxy-wide distributions may differ from a single universal form.
Chabrier initial mass function: An initial mass function commonly modeled by a lognormal form at low masses and a power law at high masses. Its lognormal low-mass form offers a widely used alternative to broken power laws.
Chemical evolution of galaxies: The changing abundances of chemical elements in galaxies as stars form, evolve, and return material. The number of massive stars controls the supply of many newly synthesized elements.

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