# Can the removal of molecular cloud envelopes by external feedback affect the efficiency of star formation?

## TL;DR

This study uses simulations to demonstrate that removing the envelopes of molecular clouds via external feedback consistently reduces star formation efficiency, especially in less bound clouds, impacting their ability to form stars.

## Contribution

It provides the first detailed numerical evidence that envelope removal by feedback decreases star formation efficiency across different cloud masses and binding energies.

## Key findings

- Envelope removal leads to a significant decrease in SFE.
- Less bound clouds experience the greatest reduction in star formation.
- SFE reduction occurs even at later evolutionary stages.

## Abstract

We investigate how star formation efficiency can be significantly decreased by the removal of a molecular cloud's envelope by feedback from an external source. Feedback from star formation has difficulties halting the process in dense gas but can easily remove the less dense and warmer envelopes where star formation does not occur. However, the envelopes can play an important role keeping their host clouds bound by deepening the gravitational potential and providing a constraining pressure boundary. We use numerical simulations to show that removal of the cloud envelopes results in all cases in a fall in the star formation efficiency (SFE). At 1.38 free-fall times our 4 pc cloud simulation experienced a drop in the SFE from 16 to six percent, while our 5 pc cloud fell from 27 to 16 per cent. At the same time, our 3 pc cloud (the least bound) fell from an SFE of 5.67 per cent to zero when the envelope was lost. The star formation efficiency per free-fall time varied from zero to $\approx$ 0.25 according to $\alpha$, defined to be the ratio of the kinetic plus thermal to gravitational energy, and irrespective of the absolute star forming mass available. Furthermore the fall in SFE associated with the loss of the envelope is found to even occur at later times. We conclude that the SFE will always fall should a star forming cloud lose its envelope due to stellar feedback, with less bound clouds suffering the greatest decrease.