Accretion and Feedback in Star Cluster Formation
  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.
