We use numerical hydrodynamic simulations to investigate prestellar core formation in the dynamic environment of giant molecular clouds, focusing on planar post-shock layers produced by colliding turbulent flows. A key goal is to test how core evolution and properties depend on the velocity dispersion in the parent cloud; our simulation suite consists of 180 models with inflow Mach numbers Ma=v/c_s=1.1-9. At all Mach numbers, our models show that turbulence and self-gravity collect gas within post-shock regions into filaments at the same time as overdense areas within these filaments condense into cores. This morphology, together with the subsonic velocities we find inside cores, is similar to observations. We extend previous results showing that core collapse develops in an ``outside-in'' manner, with density and velocity approaching the Larson-Penston asymptotic solution. The time for the first core to collapse varies as 1/sqrt(v), consistent with analytic estimates. Core building takes 10 times as long as core collapse, consistent with observed prestellar core lifetimes. Core shapes change from oblate to prolate as they evolve. To define cores, we use isosurfaces of the gravitational potential. We compare to cores defined using the potential computed from projected surface density, finding good agreement for core masses and sizes; this offers a new way to identify cores in observed maps. Cores with masses varying by three orders of magnitude (0.05 - 50 M_sun) are identified in our simulations. Stability analysis of post-shock layers predicts that the first core to collapse will have mass M \propto v^-1/2, and that the minimum mass for cores formed at late times will have M\propto v^-1. From our simulations, the median mass lies between these two relations.
The Astrochemical Evolution of Turbulent Giant Molecular Clouds : I - Physical Processes and Method of Solution for Hydrodynamic, Embedded Starless Clouds
The slope of the power spectrum of the density field in isothermal supersonic compressible turbulence
ENS de Lyon, CRAL UMR5574, Universite Claude Bernard Lyon 1, CNRS（里昂高等师范学校，CRAL UMR5574，克洛德·贝尔纳里昂大学，法国国家科学研究中心）；School of Physics, University of Exeter（埃克塞特大学物理学院）
