The influence of the cloud virial parameter on the initial mass function

Abstract

Crucial for star formation is the interplay between gravity and turbulence. The observed cloud virial parameter, $\alpha_{\mathrm{vir}}$, which is the ratio of twice the turbulent kinetic energy to the gravitational energy, is found to vary significantly in different environments, where the scatter among individual star-forming clouds can exceed an order of magnitude. Therefore, a strong dependence of the initial mass function (IMF) on $\alpha_{\mathrm{vir}}$ may challenge the notion of a universal IMF. To determine the role of $\alpha_{\mathrm{vir}}$ on the IMF, we compare the star-particle mass functions obtained in high-resolution magnetohydrodynamical simulations including jet and heating feedback, with $\alpha_{\mathrm{vir}}=0.0625$, $0.125$, and $0.5$. We find that varying $\alpha_{\mathrm{vir}}$ from $\alpha_{\mathrm{vir}}\sim0.5$ to $\alpha_{\mathrm{vir}}<0.1$ shifts the peak of the IMF to lower masses by a factor of $\sim2$ and increases the star formation rate by a similar factor. The dependence of the IMF and star formation rate on $\alpha_{\mathrm{vir}}$ is non-linear, with the dependence subsiding at $\alpha_{\mathrm{vir}}<0.1$. Our study shows a systematic dependence of the IMF on $\alpha_{\mathrm{vir}}$. Yet, it may not be measurable easily in observations, considering the uncertainties, and the relatively weak dependence found in this study.