2017ApJ...849..128C

We estimate the fraction of stars that form in compact clusters (bound and unbound), Γ_F, in a diverse sample of eight star-forming galaxies, including two irregulars, two dwarf starbursts, two spirals, and two mergers. The average value for our sample is Γ_F~24 % ±9 % . We also calculate the fraction of stars in clusters that survive to ages between τ₁ and τ₂, denoted by Γ_S(τ₁,τ₂), and find Γ_S(10,100)=4.6 % ±2.5 % and Γ_S(100,400)=2.4 % ±1.1 % , significantly lower than Γ_F for the same galaxies. We do not find any systematic trends in Γ_F or Γ_S with the star formation rate (SFR), the SFR per unit area (Σ_SFR), or the surface density of molecular gas (Σ_H2_) within the host galaxy. Our results are consistent with those found previously from the CMF/SFR statistic (where CMF is the cluster mass function), and with the quasi-universal model in which clusters in different galaxies form and disrupt in similar ways. Our results, however, contradict many previous claims that the fraction of stars in bound clusters increases strongly with Σ_SFR and Σ_H2_. We find that the previously reported trends are largely driven by comparisons that mixed Γ_F~Γ_S(0,10) and Γ_S(10,100), where Γ_S(0,10) was systematically used for galaxies with higher Σ_SFR and Σ_H2_, and Γ_S(10,100) for galaxies with lower Σ_SFR and Σ_H2_.