GMC Collisions as Triggers of Star Formation. III. Density and
  Magnetically Regulated Star Formation
  We study giant molecular cloud (GMC) collisions and their ability to trigger
star cluster formation. We further develop our three dimensional magnetized,
turbulent, colliding GMC simulations by implementing star formation sub-grid
models. Two such models are explored: (1) "Density-Regulated," i.e., fixed
efficiency per free-fall time above a set density threshold; (2)
"Magnetically-Regulated," i.e., fixed efficiency per free-fall time in regions
that are magnetically supercritical. Variations of parameters associated with
these models are also explored. In the non-colliding simulations, the overall
level of star formation is sensitive to model parameter choices that relate to
effective density thresholds. In the GMC collision simulations, the final star
formation rates and efficiencies are relatively independent of these
parameters. Between non-colliding and colliding cases, we compare the
morphologies of the resulting star clusters, properties of star-forming gas,
time evolution of the star formation rate (SFR), spatial clustering of the
stars, and resulting kinematics of the stars in comparison to the natal gas. We
find that typical collisions, by creating larger amounts of dense gas, trigger
earlier and enhanced star formation, resulting in 10 times higher SFRs and
efficiencies. The star clusters formed from GMC collisions show greater spatial
sub-structure and more disturbed kinematics.
