The effect of stellar winds on the formation of a protocluster

We present Smoothed Particle Hydrodynamics simulations of protoclusters including the effects of the stellar winds from massive stars. Using a particle–injection method, we investigate the effect of structure in close proximity to the wind sources and the short–timescale influence of winds on protoclusters. We find that structures such as disks and gaseous filaments have a strong collimating effect on winds. By a different technique of injecting momentum from point sources into our simulations, we compare the large–scale and long–term effects of isotropic and intrinsically–collimated winds on protoclusters and find them to be similar, although the collimated winds take longer to exert a significant influence. We find that both types of wind are able to dramatically slow the global star formation process, but that the timescale on which they can expel significant quantities of mass from the cluster is rather long (approaching ten freefall times). Clusters may then experience rapid star formation very early in their lifetimes, before switching to a mode where gas is gradually expelled, while star formation proceeds much more slowly over many freefall times. This complicates any conclusions regarding slow star formation derived from measuring the star–formation efficiency per freefall time. We find that estimates of the efficacy of winds in dispersing clusters derived simply from the total wind momentum flux may not be very reliable. This is due to material being expelled from deep within stellar potential wells, ofen to velocities well in excess of the cluster escape velocity, and also to the loss of momentum flux through holes in the gas distribtuion. Winds have little effect on the accretion–driven stellar initial mass function (IMF) except at the very high–mass end, where they serve to prevent some of the most massive objects accreting more material. Feedback does not result in the formation of further massive stars through the monolithic collapse of massive cores. We also find that the morphology of the gas, the rapid motions of the wind sources and the action of large–scale accretion flows prevent the formation of bubble–like structures. These effects may make it difficult to discern the influence of winds on very young clusters.