Accretion and Feedback in Star Cluster Formation

TL;DR

This paper investigates how accretion and various feedback mechanisms influence the formation and evolution of star clusters over extended periods, highlighting the complex interplay that determines gas retention and star formation efficiency.

Contribution

It provides an analytical framework to assess the dynamical state of gas in forming clusters, considering multiple feedback processes and their impact on accretion and gas expulsion.

Findings

Feedback often cannot expel gas in massive, rapidly-accreting clusters.

Feedback can inhibit accretion on larger scales, affecting cluster growth.

Star formation persists over several crossing times despite feedback effects.

Abstract

Star cluster formation is unlikely to be a sudden event: instead, matter will flow to a cluster's formation site over an extended period, even as stars form and inject energy to the region. A cluster's gaseous precursor must persist under the competing influences of accretion and feedback for several crossing times, insofar as star formation is a slow process. The new-born stellar cluster should therefore preserve a memory of this competition. Using analytical approximations we assess the dynamical state of the gas, mapping regimes in which various types of feedback are weak or strong. Protostellar outflows, radiation pressure, and ionized gas pressure are accounted for. Comparison to observations shows that feedback is often incapable of expelling gas in the more massive, rapidly-accreting clusters, but feedback may nevertheless starve accretion by acting on larger scales.