Inefficient star formation through turbulence, magnetic fields and feedback

TL;DR

This paper uses high-resolution simulations to investigate how turbulence, magnetic fields, and feedback mechanisms regulate star formation, showing that their combined effects can produce star formation rates close to observed values.

Contribution

It demonstrates through simulations that turbulence, magnetic fields, and feedback collectively reduce star formation rates, providing a more realistic model of star formation efficiency.

Findings

Including all physical processes yields SFR_ff ≈ 0.04

Turbulence, magnetic fields, and feedback reduce SFR by factors of 2-3 each

Models with turbulence and magnetic fields match observed star formation rates

Abstract

Star formation is inefficient. Only a few percent of the available gas in molecular clouds forms stars, leading to the observed low star formation rate (SFR). The same holds when averaged over many molecular clouds, such that the SFR of whole galaxies is again surprisingly low. Indeed, considering the low temperatures, molecular clouds should be highly gravitationally unstable and collapse on their global mean freefall timescale. And yet, they are observed to live about 10-100 times longer, i.e., the SFR per freefall time (SFR_ff) is only a few percent. Thus, other physical mechanisms must counteract the quick global collapse. Turbulence, magnetic fields and stellar feedback have been proposed as regulating agents, but it is still unclear which of these processes is the most important and what their relative contributions are. Here we run high-resolution simulations including gravity, turbulence, magnetic fields, and jet/outflow feedback. We confirm that clouds collapse on a mean freefall time, if only gravity is considered, producing stars at an unrealistic rate. In contrast, if turbulence, magnetic fields, and feedback are included step-by-step, the SFR is reduced by a factor of 2-3 with each additional physical ingredient. When they all act in concert, we find a constant SFR_ff = 0.04, currently the closest match to observations, but still about a factor of 2-4 higher than the average. A detailed comparison with other simulations and with observations leads us to conclude that only models with turbulence producing large virial parameters, and including magnetic fields and feedback can produce realistic SFRs.