Clustered Star Formation in Magnetic Clouds: Properties of Dense Cores
  Formed in Outflow-Driven Turbulence
  We investigate the physical properties of dense cores formed in turbulent,
magnetized, parsec-scale clumps of molecular clouds, using three-dimensional
numerical simulations that include protostellar outflow feedback. The dense
cores are identified in the simulated density data cube through a clumpfind
algorithm. We find that the core velocity dispersion does not show any clear
dependence on the core size, in contrast to Larson's linewidth-size relation,
but consistent with recent observations. In the absence of a magnetic field,
the majority of the cores have supersonic velocity dispersions. A
moderately-strong magnetic field reduces the dispersion to a subsonic or at
most transonic value typically. Most of the cores are out of virial
equilibrium, with the external pressure dominating the self-gravity. The
implication is that the core evolution is largely controlled by the
outflow-driven turbulence. Even an initially-weak magnetic field can retard
star formation significantly, because the field is amplified by the
outflow-driven turbulence to an equipartition strength, with the distorted
field component dominating the uniform one. In contrast, for a
moderately-strong field, the uniform component remains dominant. Such a
difference in the magnetic structure is evident in our simulated polarization
maps of dust thermal emission; it provides a handle on the field strength.
Recent polarization measurements show that the field lines in cluster-forming
clumps are spatially well-ordered. It is indicative of a moderately-strong,
dynamically important, field which, in combination with outflow feedback, can
keep the rate of star formation in embedded clusters at the
observationally-inferred, relatively-slow rate of several percent per free-fall
time.
