The mmax-Mecl relation, the IMF and IGIMF: probabilistically sampled functions?

TL;DR

This paper introduces a new method to analyze the maximum stellar mass in clusters, showing that observed data contradicts the idea of random sampling from a universal IMF, supporting the IGIMF theory.

Contribution

It presents a novel probabilistic approach to measure mmax dispersion and provides evidence against random sampling from a universal IMF, favoring the IGIMF model.

Findings

Observed mmax data is inconsistent with random sampling from a universal IMF.

Most scatter in mmax-Mecl data is due to observational uncertainties.

Data supports the IGIMF theory over scale-free star formation.

Abstract

We introduce a new method to measure the dispersion of mmax values of star clusters and show that the observed sample of mmax is inconsistent with random sampling from an universal stellar initial mass function (IMF) at a 99.9% confidence level. The scatter seen in the mmax-Mecl data can be mainly (76%) understood as being the result of observational uncertainties only. The scatter of mmax values at a given Mecl are consistent with mostly measurement uncertainties such that the true (physical) scatter may be very small. Additionally, new data on the local star-formation regions Taurus-Auriga and L1641 in Orion make stochastically formed stellar populations rather unlikely. The data are however consistent with the local IGIMF (integrated galactic stellar initial mass function) theory according to which a stellar population is a sum of individual star-forming events each of which is described by well defined physical laws. Randomly sampled IMFs and henceforth scale-free star formation seems to be in contradiction to observed reality.