Formation and Collapse of Quiescent Cloud Cores Induced by Dynamic Compressions

Abstract

(Abridged) We present numerical hydrodynamical simulations of the formation, evolution and gravitational collapse of isothermal molecular cloud cores. A compressive wave is set up in a constant sub-Jeans density distribution of radius r = 1 pc. As the wave travels through the simulation grid, a shock-bounded spherical shell is formed. The inner shock of this shell reaches and bounces off the center, leaving behind a central core with an initially almost uniform density distribution, surrounded by an envelope consisting of the material in the shock-bounded shell, with a power-law density profile that at late times approaches a logarithmic slope of -2 even in non-collapsing cases. The resulting density structure resembles a quiescent core of radius < 0.1 pc, with a Bonnor-Ebert-like (BE-like) profile, although it has significant dynamical differences: it is initially non-self-gravitating and confined by the ram pressure of the infalling material, and consequently, growing continuously in mass and size. With the appropriate parameters, the core mass eventually reaches an effective Jeans mass, at which time the core begins to collapse. Thus, there is necessarily a time delay between the appearance of the core and the onset of its collapse, but this is not due to the dissipation of its internal turbulence as it is often believed. These results suggest that pre-stellar cores may approximate Bonnor-Ebert structures which are however of variable mass and may or may not experience gravitational collapse, in qualitative agreement with the large observed frequency of cores with BE-like profiles.

Accepted for publication in ApJ. Associated mpeg files can be found in http://www.astrosmo.unam.mx/~g.gomez/publica.html

References in corpus (4)

• Molecular Cloud Evolution II. From cloud formation to the early stages of star formation in decaying conditions
• New Self-Similar Solutions of Polytropic Gas Dynamics
• Supersonic turbulence in shock-bound interaction zones I: symmetric settings
• Self-Similar Shocks in Polytropic Gas Flows around Star-Forming Regions

Cited by in corpus (14)

• The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure
• The Nature of the Velocity Field in Molecular Clouds. I. The Non-Magnetic Case
• Protostar Formation in Supersonic Flows: Growth and Collapse of Spherical Cores
• An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus Molecular Cloud : I. Physical Properties of Filaments and Dense cores
• Statistics of Core Lifetimes in Numerical Simulations of Turbulent, Magnetically Supercritical Molecular Clouds
• Molecular Cloud Cores with High Deuterium Fraction: Nobeyama Single-Pointing Survey
• Molecular Cloud Cores with High Deuterium Fractions: Nobeyama Mapping Survey
• A search for pre- and proto-brown dwarfs in the dark cloud Barnard 30 with ALMA
• ALMA observations of the early stages of substellar formation in the Lupus 1 and 3 molecular clouds
• Nobeyama Survey of Inward Motions toward Cores in Orion Identified by SCUBA-2
• Very Large Array Ammonia Observations of the HH 111/HH 121 Protostellar System: a Detection of a New Source With a Peculiar Chemistry
• Prestellar Cores in Turbulent Clouds: Numerical Modeling and Evolution to Collapse
• Rebounding Cores to Build Star Cluster Multiple Populations
• Why do some cores remain starless ?