The efficiency of star formation in clustered and distributed regions

TL;DR

This study uses numerical simulations to analyze how star formation efficiency varies in clustered versus distributed regions within a molecular cloud, revealing that local gravitational binding influences star formation modes and the initial mass function.

Contribution

It demonstrates the impact of local gravitational binding on star formation modes and the initial mass function within a single molecular cloud, highlighting the variation in efficiency between regions.

Findings

Star formation efficiency varies from less than 1% in distributed regions to about 40% in clusters.

Bound regions form a full initial mass function, unbound regions lack high- and low-mass stars.

Overall cloud efficiency is about 15%, but the time-averaged efficiency is only 4%, suggesting rapid star formation.

Abstract

We investigate the formation of both clustered and distributed populations of young stars in a single molecular cloud. We present a numerical simulation of a 10,000 solar mass elongated, turbulent, molecular cloud and the formation of over 2500 stars. The stars form both in stellar clusters and in a distributed mode which is determined by the local gravitational binding of the cloud. A density gradient along the major axis of the cloud produces bound regions that form stellar clusters and unbound regions that form a more distributed population. The initial mass function also depends on the local gravitational binding of the cloud with bound regions forming full IMFs whereas in the unbound, distributed regions the stellar masses cluster around the local Jeans mass and lack both the high-mass and the low-mass stars. The overall efficiency of star formation is ~ 15 % in the cloud when the calculation is terminated, but varies from less than 1 % in the the regions of distributed star formation to ~ 40 % in regions containing large stellar clusters. Considering that large scale surveys are likely to catch clouds at all evolutionary stages, estimates of the (time-averaged) star formation efficiency for the giant molecular cloud reported here is only ~ 4 %. This would lead to the erroneous conclusion of 'slow' star formation when in fact it is occurring on a dynamical timescale.