Enhanced Core Formation Rate in a Turbulent Cloud by Self-gravity

TL;DR

This study demonstrates that self-gravity significantly enhances core formation rates in turbulent molecular clouds, leading to higher density tails in the density PDF and suggesting modifications to existing star formation theories.

Contribution

It provides numerical evidence that self-gravity increases core formation rates and alters density PDFs, challenging models based solely on lognormal distributions.

Findings

Self-gravity increases the core formation rate by about 30 times.

Density PDFs develop power-law tails after self-gravity is activated.

Core formation models based on lognormal PDFs may underestimate actual rates.

Abstract

We performed a numerical experiment designed for core formation in a self-gravitating, magnetically supercritical, supersonically turbulent, isothermal cloud. A density probability distribution function (PDF) averaged over a converged turbulent state before turning self-gravity on is well-fitted with a lognormal distribution. However, after turning self-gravity on, the volume fractions of density PDFs at a high density tail, compared with the lognormal distribution, increase as time goes on. In order to see the effect of self-gravity on core formation rates, we compared the core formation rate per free-fall time (CFR$_{\rm ff}$) from the theory based on the lognormal distribution and the one from our numerical experiment. For our fiducial value of a critical density, 100, normalised with an initial value, the latter CFR$_{\rm ff}$ is about 30 times larger the former one. Therefore, self-gravity plays an important role in significantly increasing CFR$_{\rm ff}$. This result implies that core (star) formation rates or core (stellar) mass functions predicted from theories based on the lognormal density PDF need some modifications. Our result of the increased volume fraction of density PDFs after turning self-gravity on is consistent with power-law like tails commonly observed at higher ends of visual extinction PDFs of active star-forming clouds.