On the origin of the Schechter-like mass function of young star clusters in disk galaxies

TL;DR

This paper explains why the galaxy-wide mass function of young star clusters appears as a Schechter function, despite local cluster mass functions being power laws, by modeling the radial variation of cluster formation in disk galaxies.

Contribution

It introduces a model linking local power-law cluster mass functions with a galaxy-wide Schechter function through radial integration in disk galaxies.

Findings

Galaxy-wide cluster mass function has a Schechter shape due to radial integration.

Massive clusters form predominantly near galaxy centers.

Local cluster mass functions are power laws with an upper mass limit.

Abstract

The mass function of freshly formed star clusters is empirically often described as a power law. However the cluster mass function of populations of young clusters over the scale of a galaxy has been found to be described by a Schechter-function. Here we address this apparent discrepancy. We assume that in an annulus of an isolated self- regulated radially-exponential axially-symmetric disk galaxy, the local mass function of very young (embedded) clusters is a power law with an upper mass limit which depends on the local star formation rate density. Radial integration of this mass function yields a galaxy-wide embedded cluster mass function. This integrated embedded cluster mass function has a Schechter-type form, which results from the addition of many low mass clusters forming at all galactocentric distances and rarer massive clusters only forming close to the center of the galaxy.