Outflow Feedback Regulated Massive Star Formation in Parsec-Scale Cluster-Forming Clumps

We investigate massive star formation in turbulent, magnetized, parsec-scale clumps of molecular clouds including protostellar outflow feedback using three-dimensional numerical simulations of effective resolution 2048³. The calculations are carried out using a block structured adaptive mesh refinement code that solves the ideal magnetohydrodynamic equations including self-gravity and implements accreting sink particles. We find that, in the absence of regulation by magnetic fields and outflow feedback, massive stars form readily in a turbulent, moderately condensed clump of ~1600 M _sun (containing ~10² initial Jeans masses), along with a cluster of hundreds of lower mass stars. The massive stars are fed at high rates by (1) transient dense filaments produced by large-scale turbulent compression at early times and (2) by the clump-wide global collapse resulting from turbulence decay at late times. In both cases, the bulk of the massive star's mass is supplied from outside a 0.1 pc-sized "core" that surrounds the star. In our simulation, the massive star is clump-fed rather than core-fed. The need for large-scale feeding makes the massive star formation prone to regulation by outflow feedback, which directly opposes the feeding processes. The outflows reduce the mass accretion rates onto the massive stars by breaking up the dense filaments that feed the massive star formation at early times, and by collectively slowing down the global collapse that fuels the massive star formation at late times. The latter is aided by a moderate magnetic field of strength in the observed range (corresponding to a dimensionless clump mass-to-flux ratio λ~ a few); the field allows the outflow momenta to be deposited more efficiently inside the clump. We conclude that the massive star formation in our simulated turbulent, magnetized, parsec-scale clump is outflow-regulated and clump-fed. An important implication is that the formation of low-mass stars in a dense clump can affect the formation of massive stars in the same clump, through their outflow feedback on the clump dynamics. In a companion paper, we discuss the properties of the lower mass cluster members formed along with the massive stars, including their mass distribution and spatial clustering.