The Astrophysical Journal | 2019
Constraints on Upper Cutoffs in the Mass Functions of Young Star Clusters
Abstract
We test claims that the power-law mass functions of young star clusters (ages $<\\mbox{few}\\times10^8~$yr) have physical upper cutoffs at $M_*\\sim10^5~M_{\\odot}$. Specifically, we perform maximum likelihood fits of the Schechter function, $\\psi(M)=dN/dM\\propto M^{-\\beta}\\mbox{exp}(-M/M_*)$, to the observed cluster mass functions in eight well-studied galaxies (LMC, SMC, NGC 4214, NGC 4449, M83, M51, Antennae, and NGC 3256). In most cases, the value of $M_*$ is indeterminant, and the maximum cluster mass $M_{\\rm max}$ is consistent with a statistical cutoff linked to sample size rather than a physical cutoff. We find weak evidence for $M_*\\sim10^5~M_{\\odot}$ in only one case (M51, at $\\sim3\\sigma$ significance) and strong evidence against this value in several cases. Our data are generally consistent with much larger cutoffs, at $M_*\\sim\\mbox{few}\\times10^6~M_{\\odot}$. This is the predicted cutoff from dynamical models in which old globular clusters and young clusters observed today formed by similar processes with similar initial mass functions.