Cluster Formation in Protostellar Outflow-driven Turbulence

Most, perhaps all, stars go through a phase of vigorous outflow duringformation. We examine, through 3D MHD simulation, the effects of protostellaroutflows on cluster formation. We find that the initial turbulence in thecluster-forming region is quickly replaced by motions generated by outflows.The protostellar outflow-driven turbulence (``protostellar turbulence'' forshort) can keep the region close to a virial equilibrium long after the initialturbulence has decayed away. We argue that there exist two types of turbulencein star-forming clouds: a primordial (or ``interstellar'') turbulence and aprotostellar turbulence, with the former transformed into the latter mostly inembedded clusters such as NGC 1333. Since the majority of stars are thought toform in clusters, an implication is that the stellar initial mass function isdetermined to a large extent by the stars themselves, through outflows whichindividually limit the mass accretion onto forming stars and collectively shapethe environments (density structure and velocity field) in which most clustermembers form. We speculate that massive cluster-forming clumps supported byprotostellar turbulence gradually evolve towards a highly centrally condensed``pivotal'' state, culminating in rapid formation of massive stars in thedensest part through accretion.Comment: 11 pages (aastex format), 2 figures submitted to ApJ