The universality hypothesis: binary and stellar populations in star clusters and galaxies

TL;DR

This paper discusses the invariance of initial binary populations across different star-forming environments and introduces a mathematical formulation to synthesize stellar populations in galaxies.

Contribution

It provides a compact mathematical formulation of the initial binary population applicable across various stellar mass regimes, enabling galaxy-wide stellar population synthesis.

Findings

Initial binary populations are invariant to star formation conditions.

A three-part IBP model covers different stellar mass regimes.

The formulation allows synthesis of entire galaxy stellar populations.

Abstract

It is possible to extract, from the observations, distribution functions of the birth dynamical properties of a stellar population, and to also infer that these are quite invariant to the physical conditions of star formation. The most famous example is the stellar IMF, and the initial binary population (IBP) seems to follow suit. A compact mathematical formulation of the IBP can be derived from the data. It has three broad parts: the IBP of the dominant stellar population (0.08-2 M_sol), the IBP of the more-massive stars and the IBP of brown dwarfs. These three mass regimes correspond to different physical regimes of star formation but not to structure in the IMF. With this formulation of the IBP it becomes possible to synthesise the stellar-population of whole galaxies.