2019ApJ...872...93M

We test claims that the power-law mass functions of young star clusters (ages <= few x 10⁸ yr) have physical upper cutoffs at M_*∼10⁵M_☉. Specifically, we perform maximum likelihood fits of the Schechter function, ψ(M)=dN/dM∝M^βexp(-M/M_*), to the observed cluster masses in eight well-studied galaxies (LMC, SMC, NGC 4214, NGC 4449, M83, M51, Antennae, and NGC 3256). In most cases, we find that a wide range of cutoff masses is permitted (10⁵M_☉≲M_*< ∞). We find a weak detection at M_*∼10⁵M_☉ in one case (M51) and strong evidence against this value in two cases. However, when we include realistic errors in cluster masses in our analysis, the constraints on M_* become weaker and there are no significant detections (even for M51). Our data are generally consistent with much larger cutoffs, at M_*∼few×10⁶M_☉. This is the predicted cutoff from dynamical models in which old globular clusters and young clusters observed today formed by similar physical processes with similar initial mass functions.